Publications by authors named "Suzanne C E H Sallevelt"

19 Publications

  • Page 1 of 1

Rapid whole exome sequencing in pregnancies to identify the underlying genetic cause in fetuses with congenital anomalies detected by ultrasound imaging.

Prenat Diagn 2020 07 5;40(8):972-983. Epub 2020 May 5.

Department of Human Genetics, Radboud University Medical Center, Radboud Institute for Health Sciences, Nijmegen, The Netherlands.

Objective: The purpose of this study was to explore the diagnostic yield and clinical utility of trio-based rapid whole exome sequencing (rWES) in pregnancies of fetuses with a wide range of congenital anomalies detected by ultrasound imaging.

Methods: In this observational study, we analyzed the first 54 cases referred to our laboratory for prenatal rWES to support clinical decision making, after the sonographic detection of fetal congenital anomalies. The most common identified congenital anomalies were skeletal dysplasia (n = 20), multiple major fetal congenital anomalies (n = 17) and intracerebral structural anomalies (n = 7).

Results: A conclusive diagnosis was identified in 18 of the 54 cases (33%). Pathogenic variants were detected most often in fetuses with skeletal dysplasia (n = 11) followed by fetuses with multiple major fetal congenital anomalies (n = 4) and intracerebral structural anomalies (n = 3). A survey, completed by the physicians for 37 of 54 cases, indicated that the rWES results impacted clinical decision making in 68% of cases.

Conclusions: These results suggest that rWES improves prenatal diagnosis of fetuses with congenital anomalies, and has an important impact on prenatal and peripartum parental and clinical decision making.
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http://dx.doi.org/10.1002/pd.5717DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7497059PMC
July 2020

Panel-Based Exome Sequencing for Neuromuscular Disorders as a Diagnostic Service.

J Neuromuscul Dis 2019 ;6(2):241-258

Department of Neurology, Donders Institute for Brain, Cognition, and Behavior, Radboud University Medical Center, Nijmegen, The Netherlands.

Background: Neuromuscular disorders (NMDs) are clinically and genetically heterogeneous. Accurate molecular genetic diagnosis can improve clinical management, provides appropriate genetic counseling and testing of relatives, and allows potential therapeutic trials.

Objective: To establish the clinical utility of panel-based whole exome sequencing (WES) in NMDs in a population with children and adults with various neuromuscular symptoms.

Methods: Clinical exome sequencing, followed by diagnostic interpretation of variants in genes associated with NMDs, was performed in a cohort of 396 patients suspected of having a genetic cause with a variable age of onset, neuromuscular phenotype, and inheritance pattern. Many had previously undergone targeted gene testing without results.

Results: Disease-causing variants were identified in 75/396 patients (19%), with variants in the three COL6-genes (COL6A1, COL6A2 and COL6A3) as the most common cause of the identified muscle disorder, followed by variants in the RYR1 gene. Together, these four genes account for almost 25% of cases in whom a definite genetic cause was identified. Furthermore, likely pathogenic variants and/or variants of uncertain significance were identified in 95 of the patients (24%), in whom functional and/or segregation analysis should be used to confirm or reject the pathogenicity. In 18% of the cases with a disease-causing variant of which we received additional clinical information, we identified a genetic cause in genes of which the associated phenotypes did not match that of the patients. Hence, the advantage of panel-based WES is its unbiased approach.

Conclusion: Whole exome sequencing, followed by filtering for NMD genes, offers an unbiased approach for the genetic diagnostics of NMD patients. This approach could be used as a first-tier test in neuromuscular disorders with a high suspicion of a genetic cause. With uncertain results, functional testing and segregation analysis are needed to complete the evidence.
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http://dx.doi.org/10.3233/JND-180376DOI Listing
December 2019

Correction: The ARID1B spectrum in 143 patients: from nonsyndromic intellectual disability to Coffin-Siris syndrome.

Authors:
Pleuntje J van der Sluijs Sandra Jansen Samantha A Vergano Miho Adachi-Fukuda Yasemin Alanay Adila AlKindy Anwar Baban Allan Bayat Stefanie Beck-Wödl Katherine Berry Emilia K Bijlsma Levinus A Bok Alwin F J Brouwer Ineke van der Burgt Philippe M Campeau Natalie Canham Krystyna Chrzanowska Yoyo W Y Chu Brain H Y Chung Karin Dahan Marjan De Rademaeker Anne Destree Tracy Dudding-Byth Rachel Earl Nursel Elcioglu Ellen R Elias Christina Fagerberg Alice Gardham Blanca Gener Erica H Gerkes Ute Grasshoff Arie van Haeringen Karin R Heitink Johanna C Herkert Nicolette S den Hollander Denise Horn David Hunt Sarina G Kant Mitsuhiro Kato Hülya Kayserili Rogier Kersseboom Esra Kilic Malgorzata Krajewska-Walasek Kylin Lammers Lone W Laulund Damien Lederer Melissa Lees Vanesa López-González Saskia Maas Grazia M S Mancini Carlo Marcelis Francisco Martinez Isabelle Maystadt Marianne McGuire Shane McKee Sarju Mehta Kay Metcalfe Jeff Milunsky Seiji Mizuno John B Moeschler Christian Netzer Charlotte W Ockeloen Barbara Oehl-Jaschkowitz Nobuhiko Okamoto Sharon N M Olminkhof Carmen Orellana Laurent Pasquier Caroline Pottinger Vera Riehmer Stephen P Robertson Maian Roifman Caroline Rooryck Fabienne G Ropers Monica Rosello Claudia A L Ruivenkamp Mahmut S Sagiroglu Suzanne C E H Sallevelt Amparo Sanchis Calvo Pelin O Simsek-Kiper Gabriela Soares Lucia Solaeche Fatma Mujgan Sonmez Miranda Splitt Duco Steenbeek Alexander P A Stegmann Constance T R M Stumpel Saori Tanabe Eyyup Uctepe G Eda Utine Hermine E Veenstra-Knol Sunita Venkateswaran Catheline Vilain Catherine Vincent-Delorme Anneke T Vulto-van Silfhout Patricia Wheeler Golder N Wilson Louise C Wilson Bernd Wollnik Tomoki Kosho Dagmar Wieczorek Evan Eichler Rolph Pfundt Bert B A de Vries Jill Clayton-Smith Gijs W E Santen

Genet Med 2019 Sep;21(9):2160-2161

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

The original version of this Article contained an error in the spelling of the author Pleuntje J. van der Sluijs, which was incorrectly given as Eline (P. J.) van der Sluijs. This has now been corrected in both the PDF and HTML versions of the Article.
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http://dx.doi.org/10.1038/s41436-018-0368-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6752317PMC
September 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.
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http://dx.doi.org/10.3389/fgene.2018.00400DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6194163PMC
October 2018

The ARID1B spectrum in 143 patients: from nonsyndromic intellectual disability to Coffin-Siris syndrome.

Authors:
Pleuntje J van der Sluijs Sandra Jansen Samantha A Vergano Miho Adachi-Fukuda Yasemin Alanay Adila AlKindy Anwar Baban Allan Bayat Stefanie Beck-Wödl Katherine Berry Emilia K Bijlsma Levinus A Bok Alwin F J Brouwer Ineke van der Burgt Philippe M Campeau Natalie Canham Krystyna Chrzanowska Yoyo W Y Chu Brain H Y Chung Karin Dahan Marjan De Rademaeker Anne Destree Tracy Dudding-Byth Rachel Earl Nursel Elcioglu Ellen R Elias Christina Fagerberg Alice Gardham Blanca Gener Erica H Gerkes Ute Grasshoff Arie van Haeringen Karin R Heitink Johanna C Herkert Nicolette S den Hollander Denise Horn David Hunt Sarina G Kant Mitsuhiro Kato Hülya Kayserili Rogier Kersseboom Esra Kilic Malgorzata Krajewska-Walasek Kylin Lammers Lone W Laulund Damien Lederer Melissa Lees Vanesa López-González Saskia Maas Grazia M S Mancini Carlo Marcelis Francisco Martinez Isabelle Maystadt Marianne McGuire Shane McKee Sarju Mehta Kay Metcalfe Jeff Milunsky Seiji Mizuno John B Moeschler Christian Netzer Charlotte W Ockeloen Barbara Oehl-Jaschkowitz Nobuhiko Okamoto Sharon N M Olminkhof Carmen Orellana Laurent Pasquier Caroline Pottinger Vera Riehmer Stephen P Robertson Maian Roifman Caroline Rooryck Fabienne G Ropers Monica Rosello Claudia A L Ruivenkamp Mahmut S Sagiroglu Suzanne C E H Sallevelt Amparo Sanchis Calvo Pelin O Simsek-Kiper Gabriela Soares Lucia Solaeche Fatma Mujgan Sonmez Miranda Splitt Duco Steenbeek Alexander P A Stegmann Constance T R M Stumpel Saori Tanabe Eyyup Uctepe G Eda Utine Hermine E Veenstra-Knol Sunita Venkateswaran Catheline Vilain Catherine Vincent-Delorme Anneke T Vulto-van Silfhout Patricia Wheeler Golder N Wilson Louise C Wilson Bernd Wollnik Tomoki Kosho Dagmar Wieczorek Evan Eichler Rolph Pfundt Bert B A de Vries Jill Clayton-Smith Gijs W E Santen

Genet Med 2019 06 8;21(6):1295-1307. Epub 2018 Nov 8.

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

Purpose: Pathogenic variants in ARID1B are one of the most frequent causes of intellectual disability (ID) as determined by large-scale exome sequencing studies. Most studies published thus far describe clinically diagnosed Coffin-Siris patients (ARID1B-CSS) and it is unclear whether these data are representative for patients identified through sequencing of unbiased ID cohorts (ARID1B-ID). We therefore sought to determine genotypic and phenotypic differences between ARID1B-ID and ARID1B-CSS. In parallel, we investigated the effect of different methods of phenotype reporting.

Methods: Clinicians entered clinical data in an extensive web-based survey.

Results: 79 ARID1B-CSS and 64 ARID1B-ID patients were included. CSS-associated dysmorphic features, such as thick eyebrows, long eyelashes, thick alae nasi, long and/or broad philtrum, small nails and small or absent fifth distal phalanx and hypertrichosis, were observed significantly more often (p < 0.001) in ARID1B-CSS patients. No other significant differences were identified.

Conclusion: There are only minor differences between ARID1B-ID and ARID1B-CSS patients. ARID1B-related disorders seem to consist of a spectrum, and patients should be managed similarly. We demonstrated that data collection methods without an explicit option to report the absence of a feature (such as most Human Phenotype Ontology-based methods) tended to underestimate gene-related features.
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http://dx.doi.org/10.1038/s41436-018-0330-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6752273PMC
June 2019

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.
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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.
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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.
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http://dx.doi.org/10.1038/s41431-017-0058-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5891491PMC
April 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.
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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.
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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.
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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.
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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.
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http://dx.doi.org/10.1093/humrep/dew356DOI Listing
March 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.
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http://dx.doi.org/10.1016/j.jpeds.2016.12.032DOI Listing
March 2017

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

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

Leigh syndrome: Resolving the clinical and genetic heterogeneity paves the way for treatment options.

Mol Genet Metab 2016 Mar 19;117(3):300-12. Epub 2015 Dec 19.

Department of Clinical Genetics, Research School GROW, Maastricht University Medical Centre, Maastricht, The Netherlands.

Leigh syndrome is a progressive neurodegenerative disorder, affecting 1 in 40,000 live births. Most patients present with symptoms between the ages of three and twelve months, but adult onset Leigh syndrome has also been described. The disease course is characterized by a rapid deterioration of cognitive and motor functions, in most cases resulting in death due to respiratory failure. Despite the high genetic heterogeneity of Leigh syndrome, patients present with identical, symmetrical lesions in the basal ganglia or brainstem on MRI, while additional clinical manifestations and age of onset varies from case to case. To date, mutations in over 60 genes, both nuclear and mitochondrial DNA encoded, have been shown to cause Leigh syndrome, still explaining only half of all cases. In most patients, these mutations directly or indirectly affect the activity of the mitochondrial respiratory chain or pyruvate dehydrogenase complex. Exome sequencing has accelerated the discovery of new genes and pathways involved in Leigh syndrome, providing novel insights into the pathophysiological mechanisms. This is particularly important as no general curative treatment is available for this devastating disorder, although several recent studies imply that early treatment might be beneficial for some patients depending on the gene or process affected. Timely, gene-based personalized treatment may become an important strategy in rare, genetically heterogeneous disorders like Leigh syndrome, stressing the importance of early genetic diagnosis and identification of new genes/pathways. In this review, we provide a comprehensive overview of the most important clinical manifestations and genes/pathways involved in Leigh syndrome, and discuss the current state of therapeutic interventions in patients.
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http://dx.doi.org/10.1016/j.ymgme.2015.12.004DOI Listing
March 2016

Preventing the transmission of mitochondrial DNA disorders using prenatal or preimplantation genetic diagnosis.

Ann N Y Acad Sci 2015 Sep 27;1350:29-36. Epub 2015 Aug 27.

Department of Neurology, Erasmus MC-Sophia Children's Hospital, Rotterdam, the Netherlands.

Mitochondrial disorders are among the most common inborn errors of metabolism; at least 15% are caused by mitochondrial DNA (mtDNA) mutations, which occur de novo or are maternally inherited. For familial heteroplasmic mtDNA mutations, the mitochondrial bottleneck defines the mtDNA mutation load in offspring, with an often high or unpredictable recurrence risk. Oocyte donation is a safe option to prevent the transmission of mtDNA disease, but the offspring resulting from oocyte donation are genetically related only to the father. Prenatal diagnosis (PND) is technically possible but usually not applicable because of limitations in predicting the phenotype. For de novo mtDNA point mutations, recurrence risks are low and PND can be offered to provide reassurance regarding fetal health. PND is also the best option for female carriers with low-level mutations demonstrating skewing to 0% or 100%. A fairly new option for preventing the transmission of mtDNA diseases is preimplantation genetic diagnosis (PGD), in which embryos with a mutant load below a mutation-specific or general expression threshold of 18% can be transferred. PGD is currently the best reproductive option for familial heteroplasmic mtDNA point mutations. Nuclear genome transfer and genome editing techniques are currently being investigated and might offer additional reproductive options for specific mtDNA disease cases.
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http://dx.doi.org/10.1111/nyas.12866DOI Listing
September 2015

Preimplantation genetic diagnosis in mitochondrial DNA disorders: challenge and success.

J Med Genet 2013 Feb;50(2):125-32

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

Background: Mitochondrial or oxidative phosphorylation diseases are relatively frequent, multisystem disorders; in about 15% of cases they are caused by maternally inherited mitochondrial DNA (mtDNA) mutations. Because of the possible severity of the phenotype, the lack of effective treatment, and the high recurrence risk for offspring of carrier females, couples wish to prevent the transmission of these mtDNA disorders to their offspring. Prenatal diagnosis is problematic for several reasons, and concern the often poor correlation between mutation percentages and disease severity and the uncertainties about the representativeness of a fetal sample. A new option for preventing transmission of mtDNA disorders is preimplantation genetic diagnosis (PGD), which circumvents these problems by transferring an embryo below the threshold of clinical expression.

Methods: We present the data on nine PGD cycles in four female carriers of mitochondrial diseases: three mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) (m.3243A>G), and one Leigh (m.8993T>G). Our threshold for transfer after PGD is 15% for the m.3243A>G mutation and 30% for the m.8993T>G mutation.

Results: All four female carriers produced embryos eligible for transfer. The m.8993T>G mutation in oocytes/embryos showed more skewing than the m.3243A>G. In about 80% of the embryos the mutation load in the individual blastomeres was fairly constant (interblastomere differences <10%). However, in around 11% (in embryos with the m.3243A>G mutation only), the mutation load differed substantially (>15%) between blastomeres of a single embryo, mostly as a result of one outlier. The m.8993T>G carrier became pregnant and gave birth to a healthy son.

Conclusions: PGD provides carriers of mtDNA mutations the opportunity to conceive healthy offspring.
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http://dx.doi.org/10.1136/jmedgenet-2012-101172DOI Listing
February 2013