Publications by authors named "Hubert J Smeets"

74 Publications

Evaluation of molecular inversion probe versus TruSeq® custom methods for targeted next-generation sequencing.

PLoS One 2020 2;15(9):e0238467. Epub 2020 Sep 2.

Department of Clinical Genetics, Maastricht University Medical Center+, Maastricht, the Netherlands.

Resolving the genetic architecture of painful neuropathy will lead to better disease management strategies. We aimed to develop a reliable method to re-sequence multiple genes in a large cohort of painful neuropathy patients at low cost. In this study, we compared sensitivity, specificity, targeting efficiency, performance and cost effectiveness of Molecular Inversion Probes-Next generation sequencing (MIPs-NGS) and TruSeq® Custom Amplicon-Next generation sequencing (TSCA-NGS). Capture probes were designed to target nine sodium channel genes (SCN3A, SCN8A-SCN11A, and SCN1B-SCN4B). One hundred sixty-six patients with diabetic and idiopathic neuropathy were tested by both methods, 70 patients were validated by Sanger sequencing. Sensitivity, specificity and performance of both techniques were comparable, and in agreement with Sanger sequencing. The average targeted regions coverage for MIPs-NGS was 97.3% versus 93.9% for TSCA-NGS. MIPs-NGS has a more versatile assay design and is more flexible than TSCA-NGS. The cost of MIPs-NGS is >5 times cheaper than TSCA-NGS when 500 or more samples are tested. In conclusion, MIPs-NGS is a reliable, flexible, and relatively inexpensive method to detect genetic variations in a large cohort of patients. In our centers, MIPs-NGS is currently implemented as a routine diagnostic tool for screening of sodium channel genes in painful neuropathy patients.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0238467PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7467307PMC
October 2020

Knockdown Results in Reduction of mtDNA Copy Number, OXPHOS Deficiency and Abnormalities in Zebrafish Embryos.

Front Cell Dev Biol 2020 12;8:381. Epub 2020 Jun 12.

Department of Genetics and Cell Biology, Maastricht University, Maastricht, Netherlands.

High mitochondrial DNA (mtDNA) copy numbers are essential for oogenesis and embryogenesis and correlate with fertility of oocytes and viability of embryos. To understand the pathology and mechanisms associated with low mtDNA copy numbers, we knocked down mitochondrial transcription factor A (), a regulator of mtDNA replication, during early zebrafish development. Reduction of using a splice-modifying morpholino (MO) resulted in a 42 ± 17% decrease in mtDNA copy number in embryos at 4 days post fertilization. Morphant embryos displayed abnormal development of the eye, brain, heart, and muscle, as well as a 50 ± 22% decrease in ATP production. Transcriptome analysis revealed a decrease in protein-encoding transcripts from the heavy strand of the mtDNA, and down-regulation of genes involved in haem production and the metabolism of metabolites, which appear to trigger increased rRNA and tRNA synthesis in the nucleoli. However, this stress or compensatory response appears to fall short as pathology emerges and expression of genes related to eye development are severely down-regulated. Taken together, this study highlights the importance of sufficient mtDNA copies for early zebrafish development. Zebrafish is an excellent model to manipulate the mtDNA bottleneck and study its effect on embryogenesis rapidly and in large numbers of offspring.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fcell.2020.00381DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7303330PMC
June 2020

Cumulative hydropathic topology of a voltage-gated sodium channel at atomic resolution.

Proteins 2020 10 13;88(10):1319-1328. Epub 2020 Jun 13.

Department of Genetics and Cell Biology, Section Clinical Genomics, Maastricht University, Maastricht, the Netherlands.

Voltage-gated sodium channels (NavChs) are biological pores that control the flow of sodium ions through the cell membrane. In humans, mutations in genes encoding NavChs can disrupt physiological cellular activity thus leading to a wide spectrum of diseases. Here, we present a topological connection between the functional architecture of a NavAb bacterial channel and accumulation of atomic hydropathicity around its pore. This connection is established via a scaling analysis methodology that elucidates how intrachannel hydropathic density variations translate into hydropathic dipole field configurations along the pore. Our findings suggest the existence of a nonrandom cumulative hydropathic topology that is organized parallel to the membrane surface so that pore's stability, as well as, gating behavior are guaranteed. Given the biophysical significance of the hydropathic effect, our study seeks to provide a computational framework for studying cumulative hydropathic topological properties of NavChs and pore-forming proteins in general.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/prot.25951DOI Listing
October 2020

Parental repeat length instability in myotonic dystrophy type 1 pre- and protomutations.

Eur J Hum Genet 2020 07 12;28(7):956-962. Epub 2020 Mar 12.

Department of Clinical Genetics, Maastricht University Medical Center+, Maastricht, The Netherlands.

Myotonic dystrophy type 1 (DM1) is caused by a CTG trinucleotide repeat expansion on chromosome 19q13.3. While DM1 premutation (36-50 repeats) and protomutation (51-80 repeats) allele carriers are mostly asymptomatic, offspring is at risk of inheriting expanded, symptom-associated, (CTG)n repeats of n > 80. In this study we aimed to evaluate the intergenerational instability of DM1 pre- and protomutation alleles, focussing on the influence of parental gender. One hundred and forty-six parent-child pairs (34 parental premutations, 112 protomutations) were retrospectively selected from the DM1 patient cohort of the Maastricht University Medical Center+. CTG repeat size of parents and children was determined by (triplet-primed) PCR followed by fragment length analysis and Southern blot analysis. Fifty-eight out of eighty-one (71.6%) paternal transmissions led to a (CTG)n repeat of n > 80 in offspring, compared with 15 out of 65 (23.1%) maternal transmissions (p < 0.001). Repeat length instability occurred for paternal (CTG)n repeats of n ≥ 45, while maternal instability did not occur until (CTG)n repeats reached a length of n ≥ 71. Transmission of premutations caused (CTG)n repeats of n > 80 in offspring only when paternally transmitted (two cases), while protomutations caused (CTG)n repeats of n > 80 in offspring in 71 cases, of which 56 (78.9%) were paternally transmitted. In conclusion, our data show that paternally transmitted pre- and protomutations were more unstable than maternally transmitted pre- and protomutations. For genetic counseling, this implies that males with a small DMPK mutation have a higher risk of symptomatic offspring compared with females. Consequently, we suggest addressing sex-dependent factors in genetic counseling of small-sized CTG repeat carriers.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41431-020-0601-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7316980PMC
July 2020

Differential effect of lacosamide on Nav1.7 variants from responsive and non-responsive patients with small fibre neuropathy.

Brain 2020 03;143(3):771-782

Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA.

Small fibre neuropathy is a common pain disorder, which in many cases fails to respond to treatment with existing medications. Gain-of-function mutations of voltage-gated sodium channel Nav1.7 underlie dorsal root ganglion neuronal hyperexcitability and pain in a subset of patients with small fibre neuropathy. Recent clinical studies have demonstrated that lacosamide, which blocks sodium channels in a use-dependent manner, attenuates pain in some patients with Nav1.7 mutations; however, only a subgroup of these patients responded to the drug. Here, we used voltage-clamp recordings to evaluate the effects of lacosamide on five Nav1.7 variants from patients who were responsive or non-responsive to treatment. We show that, at the clinically achievable concentration of 30 μM, lacosamide acts as a potent sodium channel inhibitor of Nav1.7 variants carried by responsive patients, via a hyperpolarizing shift of voltage-dependence of both fast and slow inactivation and enhancement of use-dependent inhibition. By contrast, the effects of lacosamide on slow inactivation and use-dependence in Nav1.7 variants from non-responsive patients were less robust. Importantly, we found that lacosamide selectively enhances fast inactivation only in variants from responders. Taken together, these findings begin to unravel biophysical underpinnings that contribute to responsiveness to lacosamide in patients with small fibre neuropathy carrying select Nav1.7 variants.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/brain/awaa016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7089662PMC
March 2020

A novel mitochondrial m.4414T>C MT-TM gene variant causing progressive external ophthalmoplegia and myopathy.

Neuromuscul Disord 2019 09 21;29(9):693-697. Epub 2019 Aug 21.

Highly Specialised Mitochondrial Diagnostic Laboratory, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, UK; Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, UK.

We report a novel mitochondrial m.4414T>C variant in the mt-tRNA (MT-TM) gene in an adult patient with chronic progressive external ophthalmoplegia and myopathy whose muscle biopsy revealed focal cytochrome c oxidase (COX)-deficient and ragged red fibres. The m.4414T>C variant occurs at a strongly evolutionary conserved sequence position, disturbing a canonical base pair and disrupting the secondary and tertiary structure of the mt-tRNA. Definitive evidence of pathogenicity is provided by clear segregation of m.4414T>C mutant levels with COX deficiency in single muscle fibres. Interestingly, the variant is present in skeletal muscle at relatively low levels (30%) and undetectable in accessible, non-muscle tissues from the patient and her asymptomatic brother, emphasizing the continuing requirement for a diagnostic muscle biopsy as the preferred tissue for mtDNA genetic investigations of mt-tRNA variants leading to mitochondrial myopathy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.nmd.2019.08.005DOI Listing
September 2019

Leigh syndrome caused by mutations in is associated with a better prognosis.

Ann Clin Transl Neurol 2019 03 17;6(3):515-524. Epub 2019 Feb 17.

Wellcome Centre for Mitochondrial Research Institute of Neuroscience Newcastle University Newcastle upon Tyne United Kingdom.

Objectives: Mitochondrial methionyl-tRNA formyltransferase (MTFMT) is required for the initiation of translation and elongation of mitochondrial protein synthesis Pathogenic variants in have been associated with Leigh syndrome (LS) and mitochondrial multiple respiratory chain deficiencies. We sought to elucidate the spectrum of clinical, neuroradiological and molecular genetic findings of patients with bi-allelic pathogenic variants in .

Methods: Retrospective cohort study combining new cases and previously published cases.

Results: Thirty-eight patients with pathogenic variants in were identified, including eight new cases. The median age of presentation was 14 months (range: birth to 17 years, interquartile range [IQR] 4.5 years), with developmental delay and motor symptoms being the most frequent initial manifestation. Twenty-nine percent of the patients survived into adulthood. MRI headings in pathogenic variants included symmetrical basal ganglia changes (62%), periventricular and subcortical white matter abnormalities (55%), and brainstem lesions (48%). Isolated complex I and combined respiratory chain deficiencies were identified in 31% and 59% of the cases, respectively. Reduction of the mitochondrial complex I and complex IV subunits was identified in the fibroblasts (13/13). Sixteen pathogenic variants were identified, of which c.626C>T was the most common. Seventy-four percent of the patients were alive at their last clinical review (median 6.8 years, range: 14 months to 31 years, IQR 14.5 years).

Interpretation: Patients that harbour pathogenic variants in have a milder clinical phenotype and disease progression compared to LS caused by other nuclear defects. Fibroblasts may preclude the need for muscle biopsy, to prove causality of any novel variant.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/acn3.725DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6414492PMC
March 2019

A zebrafish model to study small-fiber neuropathy reveals a potential role for GDAP1.

Mitochondrion 2019 07 22;47:273-281. Epub 2019 Jan 22.

Department of Genetics and Cell Biology, Clinical Genomics Unit, Maastricht University, P.O. Box 616, 6200 MD, Maastricht, The Netherlands.; MHeNs School for Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands.. Electronic address:

Mutations in genes involved in mitochondrial dynamics (fusion and fission) have been implicated in many peripheral neuropathies. We hypothesized that defects in these genes could result in a phenotype resembling features of small-fiber neuropathy (SFN). This was investigated in zebrafish by knocking down two genes involved in mitochondrial dynamics gdap1 (possibly fission and motility) and opa1 (fusion) using established morpholinos. Our read-outs were nerve density in the caudal fin and a behavioral response to temperature changes, both based on comparable hallmarks of SFN in patients. Knockdown of gdap1 resulted in zebrafish embryos with a reduced density of sensory neurites compared to control morpholino-injected embryos. Furthermore, these embryos demonstrated a decreased temperature-related activity. In contrast, a knockdown of opa1 did not affect the density of sensory neurites nor the temperature-related activity. However, only the opa1 morphants had an effect on mitochondrial network morphology. As we were not able to visualize the mitochondria in the neurons, it could well be that changes in the mitochondrial network remained undetected. Our data indicate that GDAP1 knockdown affects sensory neurite development, however, it is unclear if a problem in mitochondrial fission and network formation is the pathophysiological mechanism. Although we did not observe an effect of inhibiting mitochondrial fusion during development, we still propose that genes involved in mitochondrial dynamics should be screened for mutations in patients with SFN.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.mito.2019.01.002DOI Listing
July 2019

Whole Exome Sequencing Is the Preferred Strategy to Identify the Genetic Defect in Patients With a Probable or Possible Mitochondrial Cause.

Front Genet 2018 12;9:400. Epub 2018 Oct 12.

Department of Genetics and Cell Biology, Maastricht University Medical Centre, Maastricht, Netherlands.

Mitochondrial disorders, characterized by clinical symptoms and/or OXPHOS deficiencies, are caused by pathogenic variants in mitochondrial genes. However, pathogenic variants in some of these genes can lead to clinical manifestations which overlap with other neuromuscular diseases, which can be caused by pathogenic variants in non-mitochondrial genes as well. Mitochondrial pathogenic variants can be found in the mitochondrial DNA (mtDNA) or in any of the 1,500 nuclear genes with a mitochondrial function. We have performed a two-step next-generation sequencing approach in a cohort of 117 patients, mostly children, in whom a mitochondrial disease-cause could likely or possibly explain the phenotype. A total of 86 patients had a mitochondrial disorder, according to established clinical and biochemical criteria. The other 31 patients had neuromuscular symptoms, where in a minority a mitochondrial genetic cause is present, but a non-mitochondrial genetic cause is more likely. All patients were screened for pathogenic variants in the mtDNA and, if excluded, analyzed by whole exome sequencing (WES). Variants were filtered for being pathogenic and compatible with an autosomal or X-linked recessive mode of inheritance in families with multiple affected siblings and/or consanguineous parents. Non-consanguineous families with a single patient were additionally screened for autosomal and X-linked dominant mutations in a predefined gene-set. We identified causative pathogenic variants in the mtDNA in 20% of the patient-cohort, and in nuclear genes in 49%, implying an overall yield of 68%. We identified pathogenic variants in mitochondrial and non-mitochondrial genes in both groups with, obviously, a higher number of mitochondrial genes affected in mitochondrial disease patients. Furthermore, we show that 31% of the disease-causing genes in the mitochondrial patient group were not included in the MitoCarta database, and therefore would have been missed with MitoCarta based gene-panels. We conclude that WES is preferable to panel-based approaches for both groups of patients, as the mitochondrial gene-list is not complete and mitochondrial symptoms can be secondary. Also, clinically and genetically heterogeneous disorders would require sequential use of multiple different gene panels. We conclude that WES is a comprehensive and unbiased approach to establish a genetic diagnosis in these patients, able to resolve multi-genic disease-causes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fgene.2018.00400DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6194163PMC
October 2018

Expression of pathogenic SCN9A mutations in the zebrafish: A model to study small-fiber neuropathy.

Exp Neurol 2019 01 11;311:257-264. Epub 2018 Oct 11.

Department of Clinical Genetics, Maastricht University Medical Center+, Maastricht, the Netherlands; GROW-School for Oncology and Developmental Biology, Maastricht University, Maastricht, the Netherlands.

Small-fiber neuropathy (SFN) patients experience a spectrum of sensory abnormalities, including attenuated responses to non-noxious temperatures in combination with a decreased density of the small-nerve fibers. Gain-of-function mutations in the voltage-gated sodium channels SCN9A, SCN10A and SCN11A have been identified as an underlying genetic cause in a subpopulation of patients with SFN. Based on clinical-diagnostic tests for SFN, we have set up a panel of two read-outs reflecting SFN in zebrafish, being nerve density and behavioral responses. Nerve density was studied using a transgenic line in which the sensory neurons are GFP-labelled. For the behavioral experiments, a temperature-controlled water compartment was developed. This device allowed quantification of the behavioral response to temperature changes. By using these read-outs we demonstrated that zebrafish embryos transiently overexpressing the pathogenic human SCN9A p.(I228M) or p.(G856D) mutations both have a significantly decreased density of the small-nerve fibers. Additionally, larvae overexpressing the p.(I228M) mutation displayed a significant increase in activity induced by temperature change. As these features closely resemble the clinical hallmarks of SFN, our data suggest that transient overexpression of mutant human mRNA provides a model for SFN in zebrafish. This disease model may provide a basis for testing the pathogenicity of novel genetic variants identified in SFN patients. Furthermore, this model could be used for studying SFN pathophysiology in an in vivo model and for testing therapeutic interventions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.expneurol.2018.10.008DOI Listing
January 2019

Clinical, biochemical and genetic spectrum of 70 patients with ACAD9 deficiency: is riboflavin supplementation effective?

Orphanet J Rare Dis 2018 07 19;13(1):120. Epub 2018 Jul 19.

Institute of Human Genetics, Technische Universität München, Trogerstrasse 32, 81675, Munich, Germany.

Background: Mitochondrial acyl-CoA dehydrogenase family member 9 (ACAD9) is essential for the assembly of mitochondrial respiratory chain complex I. Disease causing biallelic variants in ACAD9 have been reported in individuals presenting with lactic acidosis and cardiomyopathy.

Results: We describe the genetic, clinical and biochemical findings in a cohort of 70 patients, of whom 29 previously unpublished. We found 34 known and 18 previously unreported variants in ACAD9. No patients harbored biallelic loss of function mutations, indicating that this combination is unlikely to be compatible with life. Causal pathogenic variants were distributed throughout the entire gene, and there was no obvious genotype-phenotype correlation. Most of the patients presented in the first year of life. For this subgroup the survival was poor (50% not surviving the first 2 years) comparing to patients with a later presentation (more than 90% surviving 10 years). The most common clinical findings were cardiomyopathy (85%), muscular weakness (75%) and exercise intolerance (72%). Interestingly, severe intellectual deficits were only reported in one patient and severe developmental delays in four patients. More than 70% of the patients were able to perform the same activities of daily living when compared to peers.

Conclusions: Our data show that riboflavin treatment improves complex I activity in the majority of patient-derived fibroblasts tested. This effect was also reported for most of the treated patients and is mirrored in the survival data. In the patient group with disease-onset below 1 year of age, we observed a statistically-significant better survival for patients treated with riboflavin.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s13023-018-0784-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6053715PMC
July 2018

Anatomic & metabolic brain markers of the m.3243A>G mutation: A multi-parametric 7T MRI study.

Neuroimage Clin 2018 31;18:231-244. Epub 2018 Jan 31.

Department of Cognitive Neuroscience, Maastricht University, PO Box 616, 6200MD Maastricht, Netherlands. Electronic address:

One of the most common mitochondrial DNA (mtDNA) mutations, the A to G transition at base pair 3243, has been linked to changes in the brain, in addition to commonly observed hearing problems, diabetes and myopathy. However, a detailed quantitative description of m.3243A>G patients' brains has not been provided so far. In this study, ultra-high field MRI at 7T and volume- and surface-based data analyses approaches were used to highlight morphology (i.e. atrophy)-, microstructure (i.e. myelin and iron concentration)- and metabolism (i.e. cerebral blood flow)-related differences between patients (N = 22) and healthy controls (N = 15). The use of quantitative MRI at 7T allowed us to detect subtle changes of biophysical processes in the brain with high accuracy and sensitivity, in addition to typically assessed lesions and atrophy. Furthermore, the effect of m.3243A>G mutation load in blood and urine epithelial cells on these MRI measures was assessed within the patient population and revealed that blood levels were most indicative of the brain's state and disease severity, based on MRI as well as on neuropsychological data. Morphometry MRI data showed a wide-spread reduction of cortical, subcortical and cerebellar gray matter volume, in addition to significantly enlarged ventricles. Moreover, surface-based analyses revealed brain area-specific changes in cortical thickness (e.g. of the auditory cortex), and in T, T* and cerebral blood flow as a function of mutation load, which can be linked to typically m.3243A>G-related clinical symptoms (e.g. hearing impairment). In addition, several regions linked to attentional control (e.g. middle frontal gyrus), the sensorimotor network (e.g. banks of central sulcus) and the default mode network (e.g. precuneus) were characterized by alterations in cortical thickness, T, T* and/or cerebral blood flow, which has not been described in previous MRI studies. Finally, several hypotheses, based either on vascular, metabolic or astroglial implications of the m.3243A>G mutation, are discussed that potentially explain the underlying pathobiology. To conclude, this is the first 7T and also the largest MRI study on this patient population that provides macroscopic brain correlates of the m.3243A>G mutation indicating potential MRI biomarkers of mitochondrial diseases and might guide future (longitudinal) studies to extensively track neuropathological and clinical changes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.nicl.2018.01.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5984598PMC
February 2019

Mutation-specific effects in germline transmission of pathogenic mtDNA variants.

Hum Reprod 2018 07;33(7):1331-1341

Department of Genetics and Cell Biology, School for Oncology and Developmental Biology (GROW), Maastricht University, Maastricht, the Netherlands.

Study Question: Does germline selection (besides random genetic drift) play a role during the transmission of heteroplasmic pathogenic mitochondrial DNA (mtDNA) mutations in humans?

Summary Answer: We conclude that inheritance of mtDNA is mutation-specific and governed by a combination of random genetic drift and negative and/or positive selection.

What Is Known Already: mtDNA inherits maternally through a genetic bottleneck, but the underlying mechanisms are largely unknown. Although random genetic drift is recognized as an important mechanism, selection mechanisms are thought to play a role as well.

Study Design, Size, Duration: We determined the mtDNA mutation loads in 160 available oocytes, zygotes, and blastomeres of five carriers of the m.3243A>G mutation, one carrier of the m.8993T>G mutation, and one carrier of the m.14487T>C mutation.

Participants/materials, Setting, Methods: Mutation loads were determined in PGD samples using PCR assays and analysed mathematically to test for random sampling effects. In addition, a meta-analysis has been performed on mutation load transmission data in the literature to confirm the results of the PGD samples.

Main Results And The Role Of Chance: By applying the Kimura distribution, which assumes random mechanisms, we found that mtDNA segregations patterns could be explained by variable bottleneck sizes among all our carriers (moment estimates ranging from 10 to 145). Marked differences in the bottleneck size would determine the probability that a carrier produces offspring with mutations markedly different than her own. We investigated whether bottleneck sizes might also be influenced by non-random mechanisms. We noted a consistent absence of high mutation loads in all our m.3243A>G carriers, indicating non-random events. To test this, we fitted a standard and a truncated Kimura distribution to the m.3243A>G segregation data. A Kimura distribution truncated at 76.5% heteroplasmy has a significantly better fit (P-value = 0.005) than the standard Kimura distribution. For the m.8993T>G mutation, we suspect a skewed mutation load distribution in the offspring. To test this hypothesis, we performed a meta-analysis on published blood mutation levels of offspring-mother (O-M) transmission for the m.3243A>G and m.8993T>G mutations. This analysis revealed some evidence that the O-M ratios for the m.8993T>G mutation are different from zero (P-value <0.001), while for the m.3243A>G mutation there was little evidence that the O-M ratios are non-zero. Lastly, for the m.14487T>G mutation, where the whole range of mutation loads was represented, we found no indications for selective events during its transmission.

Large Scale Data: All data are included in the Results section of this article.

Limitations, Reason For Caution: The availability of human material for the mutations is scarce, requiring additional samples to confirm our findings.

Wider Implications Of The Findings: Our data show that non-random mechanisms are involved during mtDNA segregation. We aimed to provide the mechanisms underlying these selection events. One explanation for selection against high m.3243A>G mutation loads could be, as previously reported, a pronounced oxidative phosphorylation (OXPHOS) deficiency at high mutation loads, which prohibits oogenesis (e.g. progression through meiosis). No maximum mutation loads of the m.8993T>G mutation seem to exist, as the OXPHOS deficiency is less severe, even at levels close to 100%. In contrast, high mutation loads seem to be favoured, probably because they lead to an increased mitochondrial membrane potential (MMP), a hallmark on which healthy mitochondria are being selected. This hypothesis could provide a possible explanation for the skewed segregation pattern observed. Our findings are corroborated by the segregation pattern of the m.14487T>C mutation, which does not affect OXPHOS and MMP significantly, and its transmission is therefore predominantly determined by random genetic drift. Our conclusion is that mutation-specific selection mechanisms occur during mtDNA inheritance, which has implications for PGD and mitochondrial replacement therapy.

Study Funding/competing Interest(s): This work has been funded by GROW-School of Oncology and Developmental Biology. The authors declare no competing interests.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/humrep/dey114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6551225PMC
July 2018

Genetic defects in mtDNA-encoded protein translation cause pediatric, mitochondrial cardiomyopathy with early-onset brain disease.

Eur J Hum Genet 2018 04 13;26(4):537-551. Epub 2018 Feb 13.

Department of Genetics and Cell Biology, Maastricht University, Maastricht, The Netherlands.

This study aims to identify gene defects in pediatric cardiomyopathy and early-onset brain disease with oxidative phosphorylation (OXPHOS) deficiencies. We applied whole-exome sequencing in three patients with pediatric cardiomyopathy and early-onset brain disease with OXPHOS deficiencies. The brain pathology was studied by MRI analysis. In consanguineous patient 1, we identified a homozygous intronic variant (c.850-3A > G) in the QRSL1 gene, which was predicted to cause abnormal splicing. The variant segregated with the disease and affected the protein function, which was confirmed by complementation studies, restoring OXPHOS function only with wild-type QRSL1. Patient 2 was compound heterozygous for two novel affected and disease-causing variants (c.[253G > A];[938G > A]) in the MTO1 gene. In patient 3, we detected one unknown affected and disease-causing variants (c.2872C > T) and one known disease-causing variant (c.1774C > T) in the AARS2 gene. The c.1774C > T variant was present in the paternal copy of the AARS2 gene, the c.2872C > T in the maternal copy. All genes were involved in translation of mtDNA-encoded proteins. Defects in mtDNA-encoded protein translation lead to severe pediatric cardiomyopathy and brain disease with OXPHOS abnormalities. This suggests that the heart and brain are particularly sensitive to defects in mitochondrial protein synthesis during late embryonic or early postnatal development, probably due to the massive mitochondrial biogenesis occurring at that stage. If both the heart and brain are involved, the prognosis is poor with a likely fatal outcome at young age.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41431-017-0058-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5891491PMC
April 2018

Human Wharton's Jelly-Derived Stem Cells Display a Distinct Immunomodulatory and Proregenerative Transcriptional Signature Compared to Bone Marrow-Derived Stem Cells.

Stem Cells Dev 2018 01 21;27(2):65-84. Epub 2017 Dec 21.

1 Biomedical Research Institute, Hasselt University , Diepenbeek, Belgium .

Mesenchymal stromal cells (MSCs) are multipotent stem cells with immunosuppressive and trophic support functions. While MSCs from different sources frequently display a similar appearance in culture, they often show differences in their surface marker and gene expression profiles. Although bone marrow is considered the "gold standard" tissue to isolate classical MSCs (BM-MSC), MSC-like cells are currently also derived from more easily accessible extra-embryonic tissues such as the umbilical cord. In this study, we defined the best way to isolate MSCs from the Wharton's jelly of the human umbilical cord (WJ-MSC) and assessed the mesenchymal and immunological phenotype of BM-MSC and WJ-MSC. Moreover, the gene expression profile of established WJ-MSC cultures was compared to two different bone marrow-derived stem cell populations (BM-MSC and multipotent adult progenitor cells or MAPC). We observed that explant culturing of Wharton's jelly matrix is superior to collagenase tissue digestion for obtaining mesenchymal-like cells, with explant isolated cells displaying increased expansion potential. While being phenotypically similar to adult MSCs, WJ-MSC show a different gene expression profile. Gene ontology analysis revealed that genes associated with cell adhesion, proliferation, and immune system functioning are enriched in WJ-MSC. In vivo transplantation confirms their immune modulatory effect on T cells, similar to BM-MSC and MAPC. Furthermore, WJ-MSC intrinsically overexpress genes involved in neurotrophic support and their secretome induces neuronal maturation of SH-SY5Y neuroblastoma cells to a greater extent than BM-MSC. This signature makes WJ-MSC an attractive candidate for cell-based therapy in neurodegenerative and immune-mediated central nervous system disorders such as multiple sclerosis, Parkinson's disease, or amyotrophic lateral sclerosis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1089/scd.2017.0029DOI Listing
January 2018

Selection and Characterization of Palmitic Acid Responsive Patients with an OXPHOS Complex I Defect.

Front Mol Neurosci 2017 18;10:336. Epub 2017 Oct 18.

Department of Clinical Genetics, Maastricht University Medical Centre, Maastricht, Netherlands.

Mitochondrial disorders are genetically and clinically heterogeneous, mainly affecting high energy-demanding organs due to impaired oxidative phosphorylation (OXPHOS). Currently, effective treatments for OXPHOS defects, with complex I deficiency being the most prevalent, are not available. Yet, clinical practice has shown that some complex I deficient patients benefit from a high-fat or ketogenic diet, but it is unclear how these therapeutic diets influence mitochondrial function and more importantly, which complex I patients could benefit from such treatment. Dietary studies in a complex I deficient patient with exercise intolerance showed increased muscle endurance on a high-fat diet compared to a high-carbohydrate diet. We performed whole-exome sequencing to characterize the genetic defect. A pathogenic homozygous p.G212V missense mutation was identified in the gene, encoding an early assembly factor of complex I. A complementation study in fibroblasts confirmed that the p.G212V mutation caused the complex I deficiency. The mechanism turned out to be an incomplete assembly of the peripheral arm of complex I, leading to a decrease in the amount of mature complex I. The patient clinically improved on a high-fat diet, which was supported by the 25% increase in maximal OXPHOS capacity in TMEM126B defective fibroblast by the saturated fatty acid palmitic acid, whereas oleic acid did not have any effect in those fibroblasts. Fibroblasts of other patients with a characterized complex I gene defect were tested in the same way. Patient fibroblasts with complex I defects in NDUFS7 and NDUFAF5 responded to palmitic acid, whereas ACAD9, NDUFA12, and NDUFV2 defects were non-responding. Although the data are too limited to draw a definite conclusion on the mechanism, there is a tendency that protein defects involved in early assembly complexes, improve with palmitic acid, whereas proteins defects involved in late assembly, do not. Our data show at a clinical and biochemical level that a high fat diet can be beneficial for complex I patients and that our cell line assay will be an easy tool for the selection of patients, who might potentially benefit from this therapeutic diet.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fnmol.2017.00336DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5651253PMC
October 2017

Preimplantation genetic diagnosis for mitochondrial DNA mutations: analysis of one blastomere suffices.

J Med Genet 2017 10 1;54(10):693-697. Epub 2017 Jul 1.

Department of Clinical Genetics, Maastricht University Medical Center+ (MUMC+), Maastricht, The Netherlands.

Background: Preimplantation genetic diagnosis (PGD) is a reproductive strategy for mitochondrial DNA (mtDNA) mutation carriers, strongly reducing their risk of affected offspring. Embryos either without the mutation or with mutation load below the phenotypic threshold are transferred to the uterus. Because of incidental heteroplasmy deviations in single blastomere and the relatively limited data available, we so far preferred relying on two blastomeres rather than one. Considering the negative effect of a two-blastomere biopsy protocol compared with a single-blastomere biopsy protocol on live birth delivery rate, we re-evaluated the error rate in our current dataset.

Methods: For the m.3243A>G mutation, sufficient embryos/blastomeres were available for a powerful analysis. The diagnostic error rate, defined as a potential false-negative result, based on a threshold of 15%, was determined in 294 single blastomeres analysed in 73 embryos of 9 female m.3243A>G mutation carriers.

Results: Only one out of 294 single blastomeres (0.34%) would have resulted in a false-negative diagnosis. False-positive diagnoses were not detected.

Conclusion: Our findings support a single-blastomere biopsy PGD protocol for the m.3243A>G mutation as the diagnostic error rate is very low. As in the early preimplantation embryo no mtDNA replication seems to occur and the mtDNA is divided randomly among the daughter cells, we conclude this result to be independent of the specific mutation and therefore applicable to all mtDNA mutations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1136/jmedgenet-2017-104633DOI Listing
October 2017

A comprehensive strategy for exome-based preconception carrier screening.

Genet Med 2017 05 27;19(5):583-592. Epub 2016 Oct 27.

Department of Clinical Genetics, Maastricht University Medical Center+ (MUMC+), Maastricht, The Netherlands.

Purpose: Whole-exome sequencing (WES) provides the possibility of genome-wide preconception carrier screening (PCS). Here, we propose a filter strategy to rapidly identify the majority of relevant pathogenic mutations.

Methods: Our strategy was developed using WES data from eight consanguineous and five fictive nonconsanguineous couples and was subsequently applied to 20 other fictive nonconsanguineous couples. Presumably pathogenic variants based on frequency and database annotations or generic characteristics and mutation type were selected in genes shared by the couple and in the female's X-chromosome. Unclassified variants were not included.

Results: This yielded an average of 29 (19-51) variants in genes shared by the consanguineous couples and 15 (6-30) shared by the nonconsanguineous couples. For X-linked variants, the numbers per female were 3 (1-5) and 1 (0-3), respectively. Remaining variants were verified manually. The majority were able to be quickly discarded, effectively leaving true pathogenic variants.

Conclusion: We conclude that WES is applicable for PCS, both for consanguineous and nonconsanguineous couples, with the remaining number of variants being manageable in a clinical setting. The addition of gene panels for filtering was not favorable because it resulted in missing pathogenic variants. It is important to develop and continuously curate databases with pathogenic mutations to further increase the sensitivity of WES-based PCS.Genet Med advance online publication 27 October 2016.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/gim.2016.153DOI Listing
May 2017

Novel SLC25A32 mutation in a patient with a severe neuromuscular phenotype.

Eur J Hum Genet 2017 06 26;25(7):886-888. Epub 2017 Apr 26.

Department of Clinical Genetics, Maastricht University Medical Centre (MUMC), Maastricht, The Netherlands.

In a 51-year-old patient of consanguineous parents with a severe neuromuscular phenotype of early-onset ataxia, myoclonia, dysarthria, muscle weakness and exercise intolerance, exome sequencing revealed a novel homozygous variant (c.-264_31delinsCTCACAAATGCTCA) in the mitochondrial FAD-transporter gene SLC25A32. Flavin adenine dinucleotide (FAD) is an essential co-factor for many mitochondrial enzymes and impaired mitochondrial FAD-transport was supported by a reduced oxidative phosphorylation complex II activity in the patient's muscle, decreased ATP production in fibroblasts, and a deficiency of mitochondrial FAD-dependent enzymes. Clinically, the patient showed improvement upon riboflavin treatment, which is a precursor of FAD. Our results confirm the recently reported case of SLC25A32 as a cause of riboflavin-responsive disease. Our patient showed a more severe clinical phenotype compared with the reported patient, corresponding with the (most likely) complete absence of the SLC25A32-encoding MFT (Mitochondrial Folate Transporter) protein.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ejhg.2017.62DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5520074PMC
June 2017

PGD for the m.14487 T>C mitochondrial DNA mutation resulted in the birth of a healthy boy.

Hum Reprod 2017 03;32(3):698-703

Department of Clinical Genetics, Maastricht University Medical Center+ (MUMC+), P. Debyelaan 25, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands.

We report on the first PGD performed for the m.14487 T>C mitochondrial DNA (mtDNA) mutation in the MT-ND6 gene, associated with Leigh syndrome. The female carrier gave birth to a healthy baby boy at age 42. This case adds to the successes of PGD for mtDNA mutations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/humrep/dew356DOI Listing
March 2017

Amiloride-sensitive cation channel 2 genotype affects the response to a carbon dioxide panic challenge.

J Psychopharmacol 2017 10 25;31(10):1294-1301. Epub 2017 Jan 25.

1 Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, the Netherlands.

Until recently, genetic research into panic disorder (PD) has had only limited success. Inspired by rodent research, demonstrating that the acid-sensing ion channel 1a (ASIC1a) is critically involved in the behavioral fear response to carbon dioxide (CO) exposure, variants in the human homologue gene amiloride-sensitive cation channel 2 (ACCN2) were shown to be associated with PD. However, the relationship between changes in brain pH and ACCN2, as done in rodents by CO exposure, has not been investigated yet in humans. Here, we examined this link between the ACCN2 gene and the response to CO exposure in two studies: in healthy volunteers as well as PD patients and using both behavioral and physiological outcome measures. More specifically, 107 healthy volunteers and 183 PD patients underwent a 35% CO inhalation. Negative affect was assessed using visual analogue scales and the panic symptom list (PSL), and, in healthy volunteers, cardiovascular measurements. The single nucleotide polymorphism rs10875995 was significantly associated with a higher emotional response in PD patients and with an increase in systolic as well as diastolic blood pressure in healthy subjects. In all measurements, subjects homozygous for the T-allele showed a heightened reactivity to CO. Furthermore, a trend towards an rs685012 genotype effect on the emotional response was found in PD patients. We provide the first evidence that genetic variants in the ACCN2 are associated with differential sensitivity to CO in PD patients as well as healthy volunteers, further supporting ACCN2 as a promising candidate for future research to improve current treatment options.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1177/0269881116686880DOI Listing
October 2017

Rapid Resolution of Blended or Composite Multigenic Disease in Infants by Whole-Exome Sequencing.

J Pediatr 2017 03 9;182:371-374.e2. Epub 2017 Jan 9.

Department of Clinical Genetics, Maastricht University Medical Centre, Maastricht, The Netherlands; Department of Genetics and Cell Biology, School for Oncology and Developmental Biology, Maastricht University Medical Centre, Maastricht, The Netherlands. Electronic address:

Whole-exome sequencing identified multiple genetic causes in 2 infants with heterogeneous disease. Three gene defects in the first patient explained all symptoms, but manifestations were overlapping (blended phenotype). Two gene defects in the second patient explained nonoverlapping symptoms (composite phenotype). Whole-exome sequencing rapidly and comprehensively resolves heterogeneous genetic disease.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jpeds.2016.12.032DOI Listing
March 2017

Specific MRI Abnormalities Reveal Severe Perrault Syndrome due to CLPP Defects.

Front Neurol 2016 16;7:203. Epub 2016 Nov 16.

Department of Clinical Genetics, Maastricht University Medical Centre, Maastricht, Netherlands; Department of Genetics and Cell Biology, School for Oncology and Developmental Biology, Maastricht University Medical Centre, Maastricht, Netherlands; Maastricht Centre for Systems Biology (MaCSBio), Maastricht, Netherlands.

In establishing a genetic diagnosis in heterogeneous neurological disease, clinical characterization and whole exome sequencing (WES) go hand-in-hand. Clinical data are essential, not only to guide WES variant selection and define the clinical severity of a genetic defect but also to identify other patients with defects in the same gene. In an infant patient with sensorineural hearing loss, psychomotor retardation, and epilepsy, WES resulted in identification of a novel homozygous frameshift mutation (c.21delA). Based on the gene defect and clinical symptoms, the diagnosis Perrault syndrome type 3 (PRLTS3) was established. The patient's brain-MRI revealed specific abnormalities of the subcortical and deep cerebral white matter and the middle blade of the corpus callosum, which was used to identify similar patients in the Amsterdam brain-MRI database, containing over 3000 unclassified leukoencephalopathy cases. In three unrelated patients with similar MRI abnormalities the gene was sequenced, and in two of them novel missense mutations were identified together with a large deletion that covered part of the gene on the other allele. The severe neurological and MRI abnormalities in these young patients were due to the drastic impact of the mutations, correlating with the variation in clinical manifestations among previously reported patients. Our data show that similarity in brain-MRI patterns can be used to identify novel PRLTS3 patients, especially during early disease stages, when only part of the disease manifestations are present. This seems especially applicable to the severely affected cases in which CLPP function is drastically affected and MRI abnormalities are pronounced.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fneur.2016.00203DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5110515PMC
November 2016

Replication Errors Made During Oogenesis Lead to Detectable De Novo mtDNA Mutations in Zebrafish Oocytes with a Low mtDNA Copy Number.

Genetics 2016 Dec 21;204(4):1423-1431. Epub 2016 Oct 21.

Department of Genetics and Cell Biology, Clinical Genomics Unit, School for Oncology and Developmental Biology, Maastricht University, 6200 MD, The Netherlands

Of all pathogenic mitochondrial DNA (mtDNA) mutations in humans, ∼25% is de novo, although the occurrence in oocytes has never been directly assessed. We used next-generation sequencing to detect point mutations directly in the mtDNA of 3-15 individual mature oocytes and three somatic tissues from eight zebrafish females. Various statistical and biological filters allowed reliable detection of de novo variants with heteroplasmy ≥1.5%. In total, we detected 38 de novo base substitutions, but no insertions or deletions. These 38 de novo mutations were present in 19 of 103 mature oocytes, indicating that ∼20% of the mature oocytes carry at least one de novo mutation with heteroplasmy ≥1.5%. This frequency of de novo mutations is close to that deducted from the reported error rate of polymerase gamma, the mitochondrial replication enzyme, implying that mtDNA replication errors made during oogenesis are a likely explanation. Substantial variation in the mutation prevalence among mature oocytes can be explained by the highly variable mtDNA copy number, since we previously reported that ∼20% of the primordial germ cells have a mtDNA copy number of ≤73 and would lead to detectable mutation loads. In conclusion, replication errors made during oogenesis are an important source of de novo mtDNA base substitutions and their location and heteroplasmy level determine their significance.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1534/genetics.116.194035DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5161276PMC
December 2016

De novo mtDNA point mutations are common and have a low recurrence risk.

J Med Genet 2017 02 22;54(2):73-83. Epub 2016 Jul 22.

Department of Clinical Genetics, Maastricht University Medical Centre (MUMC), Maastricht, The Netherlands.

Background: Severe, disease-causing germline mitochondrial (mt)DNA mutations are maternally inherited or arise de novo. Strategies to prevent transmission are generally available, but depend on recurrence risks, ranging from high/unpredictable for many familial mtDNA point mutations to very low for sporadic, large-scale single mtDNA deletions. Comprehensive data are lacking for de novo mtDNA point mutations, often leading to misconceptions and incorrect counselling regarding recurrence risk and reproductive options. We aim to study the relevance and recurrence risk of apparently de novo mtDNA point mutations.

Methods: Systematic study of prenatal diagnosis (PND) and recurrence of mtDNA point mutations in families with de novo cases, including new and published data. 'De novo' based on the absence of the mutation in multiple (postmitotic) maternal tissues is preferred, but mutations absent in maternal blood only were also included.

Results: In our series of 105 index patients (33 children and 72 adults) with (likely) pathogenic mtDNA point mutations, the de novo frequency was 24.6%, the majority being paediatric. PND was performed in subsequent pregnancies of mothers of four de novo cases. A fifth mother opted for preimplantation genetic diagnosis because of a coexisting Mendelian genetic disorder. The mtDNA mutation was absent in all four prenatal samples and all 11 oocytes/embryos tested. A literature survey revealed 137 de novo cases, but PND was only performed for 9 (including 1 unpublished) mothers. In one, recurrence occurred in two subsequent pregnancies, presumably due to germline mosaicism.

Conclusions: De novo mtDNA point mutations are a common cause of mtDNA disease. Recurrence risk is low. This is relevant for genetic counselling, particularly for reproductive options. PND can be offered for reassurance.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1136/jmedgenet-2016-103876DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5502310PMC
February 2017

Rare novel variants in the ZIC3 gene cause X-linked heterotaxy.

Eur J Hum Genet 2016 12 13;24(12):1783-1791. Epub 2016 Jul 13.

Department of Clinical Genetics, Maastricht University Medical Center, Maastricht, The Netherlands.

Variants in the ZIC3 gene are rare, but have demonstrated their profound clinical significance in X-linked heterotaxy, affecting in particular male patients with abnormal arrangement of thoracic and visceral organs. Several reports have shown relevance of ZIC3 gene variants in both familial and sporadic cases and with a predominance of mutations detected in zinc-finger domains. No studies so far have assessed the functional consequences of ZIC3 variants in an in vivo model organism. A study population of 348 patients collected over more than 10 years with a large variety of congenital heart disease including heterotaxy was screened for variants in the ZIC3 gene. Functional effects of three variants were assessed both in vitro and in vivo in the zebrafish. We identified six novel pathogenic variants (1,7%), all in either male patients with heterotaxy (n=5) or a female patient with multiple male deaths due to heterotaxy in the family (n=1). All variants were located within the zinc-finger domains or leading to a truncation before these domains. Truncating variants showed abnormal trafficking of mutated ZIC3 proteins, whereas the missense variant showed normal trafficking. Overexpression of wild-type and mutated ZIC protein in zebrafish showed full non-functionality of the two frame-shift variants and partial activity of the missense variant compared with wild-type, further underscoring the pathogenic character of these variants. Concluding, we greatly expanded the number of causative variants in ZIC3 and delineated the functional effects of three variants using in vitro and in vivo model systems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ejhg.2016.91DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5117940PMC
December 2016

Differences in Strength and Timing of the mtDNA Bottleneck between Zebrafish Germline and Non-germline Cells.

Cell Rep 2016 07 30;16(3):622-30. Epub 2016 Jun 30.

Department of Genetics and Cell Biology, Clinical Genomics Unit, School for Oncology and Developmental Biology (GROW), Maastricht University Medical Centre, 6200MD Maastricht, the Netherlands; Maastricht Centre for Systems Biology (MaCSBio), Maastricht University Medical Centre, 6200MD, the Netherlands. Electronic address:

We studied the mtDNA bottleneck in zebrafish to elucidate size, timing, and variation in germline and non-germline cells. Mature zebrafish oocytes contain, on average, 19.0 × 10(6) mtDNA molecules with high variation between oocytes. During embryogenesis, the mtDNA copy number decreases to ∼170 mtDNA molecules per primordial germ cell (PGC), a number similar to that in mammals, and to ∼50 per non-PGC. These occur at the same developmental stage, implying considerable variation in mtDNA copy number in (non-)PGCs of the same female, dictated by variation in the mature oocyte. The presence of oocytes with low mtDNA numbers, if similar in humans, could explain how (de novo) mutations can reach high mutation loads within a single generation. High mtDNA copy numbers in mature oocytes are established by mtDNA replication during oocyte development. Bottleneck differences between germline and non-germline cells, due to early differentiation of PGCs, may account for different distribution patterns of familial mutations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2016.06.023DOI Listing
July 2016

Polyhydramnios and cerebellar atrophy: a prenatal presentation of mitochondrial encephalomyopathy caused by mutations in the FBXL4 gene.

Clin Case Rep 2016 Apr 16;4(4):425-8. Epub 2016 Mar 16.

Department of Clinical Genetics Leiden University Medical Centre Leiden Netherlands.

Severe recessive mitochondrial myopathy caused by FBXL4 gene mutations may present prenatally with polyhydramnios and cerebellar hypoplasia. Characteristic dysmorphic features are: high and arched eyebrows, triangular face, a slight upslant of palpebral fissures, and a prominent pointed chin. Metabolic investigations invariably show increased serum lactate and pyruvate levels.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ccr3.511DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4831400PMC
April 2016

Mitochondrial DNA sequence characteristics modulate the size of the genetic bottleneck.

Hum Mol Genet 2016 Mar 5;25(5):1031-41. Epub 2016 Jan 5.

Wellcome Trust Centre for Mitochondrial Research and Medical Research Council Mitochondrial Biology Unit, Cambridge, UK, Department of Clinical Neurosciences, School of Clinical Medicine, University of Cambridge, Cambridge, UK,

With a combined carrier frequency of 1:200, heteroplasmic mitochondrial DNA (mtDNA) mutations cause human disease in ∼1:5000 of the population. Rapid shifts in the level of heteroplasmy seen within a single generation contribute to the wide range in the severity of clinical phenotypes seen in families transmitting mtDNA disease, consistent with a genetic bottleneck during transmission. Although preliminary evidence from human pedigrees points towards a random drift process underlying the shifting heteroplasmy, some reports describe differences in segregation pattern between different mtDNA mutations. However, based on limited observations and with no direct comparisons, it is not clear whether these observations simply reflect pedigree ascertainment and publication bias. To address this issue, we studied 577 mother-child pairs transmitting the m.11778G>A, m.3460G>A, m.8344A>G, m.8993T>G/C and m.3243A>G mtDNA mutations. Our analysis controlled for inter-assay differences, inter-laboratory variation and ascertainment bias. We found no evidence of selection during transmission but show that different mtDNA mutations segregate at different rates in human pedigrees. m.8993T>G/C segregated significantly faster than m.11778G>A, m.8344A>G and m.3243A>G, consistent with a tighter mtDNA genetic bottleneck in m.8993T>G/C pedigrees. Our observations support the existence of different genetic bottlenecks primarily determined by the underlying mtDNA mutation, explaining the different inheritance patterns observed in human pedigrees transmitting pathogenic mtDNA mutations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/hmg/ddv626DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4754047PMC
March 2016