Publications by authors named "Lisa Emrick"

38 Publications

A novel de novo intronic variant in ITPR1 causes Gillespie syndrome.

Am J Med Genet A 2021 May 5. Epub 2021 May 5.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA.

Gillespie syndrome (GLSP) is characterized by bilateral symmetric partial aplasia of the iris presenting as a fixed and large pupil, cerebellar hypoplasia with ataxia, congenital hypotonia, and varying levels of intellectual disability. GLSP is caused by either biallelic or heterozygous, dominant-negative, pathogenic variants in ITPR1. Here, we present a 5-year-old male with GLSP who was found to have a heterozygous, de novo intronic variant in ITPR1 (NM_001168272.1:c.5935-17G > A) through genome sequencing (GS). Sanger sequencing of cDNA from this individual's fibroblasts showed the retention of 15 nucleotides from intron 45, which is predicted to cause an in-frame insertion of five amino acids near the C-terminal transmembrane domain of ITPR1. In addition, qPCR and cDNA sequencing demonstrated reduced expression of both ITPR1 alleles in fibroblasts when compared to parental samples. Given the close proximity of the predicted in-frame amino acid insertion to the site of previously described heterozygous, de novo, dominant-negative, pathogenic variants in GLSP, we predict that this variant also has a dominant-negative effect on ITPR1 channel function. Overall, this is the first report of a de novo intronic variant causing GLSP, which emphasizes the utility of GS and cDNA studies for diagnosing patients with a clinical presentation of GLSP and negative clinical exome sequencing.
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http://dx.doi.org/10.1002/ajmg.a.62232DOI Listing
May 2021

A novel ATP1A2 variant associated with severe stepwise regression, hemiplegia, epilepsy and movement disorders in two unrelated patients.

Eur J Paediatr Neurol 2021 Mar 16;31:21-26. Epub 2021 Jan 16.

Baylor College of Medicine, Department of Pediatric Neurology and Developmental Neuroscience, Houston, TX, USA.

Pathogenic variants in ATP1A2, a gene encoding the α subunit of the Na,K-ATPase, cause familial hemiplegic migraine type 2 (FHM2). In contrast, pathogenic variants in ATP1A3, an ATP1A2 paralog, cause alternating hemiplegia of childhood (AHC), a severe neurodevelopmental disorder with infantile onset hemiplegic attacks, seizures, dystonia, chorea and developmental delay. Despite high sequence homology with ATP1A3, ATP1A2 variants rarely associate with severe phenotypes resembling those linked to ATP1A3. Here we describe two unrelated patients with infantile onset hemiplegic attacks, refractory epilepsy, movement disorders, abnormal eye movements and truncal ataxia with a shared de novo variant in ATP1A2, c.2438T > A (p.Met813Lys). The variant is not found in population databases, is predicted to be damaging by in silico analysis, and affects a highly conserved residue. Both patients experienced severe attacks with unilateral cerebral edema followed by sustained, stepwise regression. This report highlights the need to sequence ATP1A2 in the workup of patients with features of AHC that do not fulfill AHC diagnostic criteria.
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http://dx.doi.org/10.1016/j.ejpn.2021.01.004DOI Listing
March 2021

-related Neurodevelopmental Disorder With Leukoencephalopathy, Developmental Delay, and Episodic Neurologic Regression Mimics Pelizaeus-Merzbacher Disease.

Neurol Genet 2021 Feb 17;7(1):e539. Epub 2020 Dec 17.

Division of Neurology and Developmental Neuroscience (D.G.C., D.T., L.F., K.P., L.T.E., H.-T.C.), Department of Pediatrics, BCM, Houston, TX; Texas Children's Hospital (D.G.C., D.T., L.F., K.P., L.T.E., H.-T.C.), Houston, TX; Department of Neurology and Neurotherapeutics (M.H.), UTSW, Dallas, TX; Department of Molecular and Human Genetics (L.T.E., H.-T.C.), BCM, Houston, TX; Department of Neuroscience (H.-T.C.), BCM, Houston, TX; Program in Development (H.-T.C.), Disease Models, and Therapeutics, BCM, Houston, TX; McNair Medical Institute (H.-T.C.), The Robert and Janice McNair Foundation, Houston, TX; and Jan and Dan Duncan Neurological Research Institute (H.-T.C.), Texas Children's Hospital, Houston, TX.

Objective: To demonstrate that de novo missense single nucleotide variants (SNVs) in cause a neurodevelopmental disorder with leukoencephalopathy resembling Pelizaeus-Merzbacher disease (PMD).

Methods: A retrospective chart review was performed of 2 unrelated males evaluated at a single institution with de novo SNVs identified by clinical exome sequencing (ES). Clinical and radiographic data were reviewed and summarized.

Results: Both individuals presented in the first year of life with concern for seizures and developmental delay. Common clinical findings included horizontal and/or pendular nystagmus during infancy, axial hypotonia, appendicular hypertonia, spasticity, and episodic neurologic regression with febrile viral illnesses. MRI of the brain demonstrated severely delayed myelination in infancy. A hypomyelinating pattern was confirmed on serial imaging at age 4 years for proband 1. In proband 2, repeat imaging at age 13 months confirmed persistent delayed myelination. These clinical and radiographic features led to a strong suspicion of PMD. However, neither copy number variants nor pathogenic SNVs were detected by chromosomal microarray and trio ES, respectively. Reanalysis of trio ES identified heterozygous de novo missense variant c.290C>T (p.Ser97Phe) in proband 1 and c.326C>T (p.Ala109Val) in proband 2.

Conclusions: The autosomal dominant -related leukoencephalopathy, developmental delay, and episodic neurologic regression syndrome should be considered in the differential diagnosis for PMD and other hypomyelinating leukodystrophies (HLDs). A characteristic history of developmental regression with febrile illnesses may help distinguish it from other HLDs.
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http://dx.doi.org/10.1212/NXG.0000000000000539DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7862097PMC
February 2021

Epilepsy and Electroencephalographic Abnormalities in SATB2-Associated Syndrome.

Pediatr Neurol 2020 11 13;112:94-100. Epub 2020 Apr 13.

Division of Neurology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania; Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.

Background: Seizures are an under-reported feature of the SATB2-associated syndrome phenotype. We describe the electroencephalographic findings and seizure semiology and treatment in a population of individuals with SATB2-associated syndrome.

Methods: We performed a retrospective review of 101 individuals with SATB2-associated syndrome who were reported to have had a previous electroencephalographic study to identify those who had at least one reported abnormal result. For completeness, a supplemental survey was distributed to the caregivers and input from the treating neurologist was obtained whenever possible.

Results: Forty-one subjects were identified as having at least one prior abnormal electroencephalography. Thirty-eight individuals (93%) had epileptiform discharges, 28 (74%) with central localization. Sleep stages were included as part of the electroencephalographies performed in 31 individuals (76%), and epileptiform activity was recorded during sleep in all instances (100%). Definite clinical seizures were diagnosed in 17 individuals (42%) with a mean age of onset of 3.2 years (four months to six years), and focal seizures were the most common type of seizure observed (42%). Six subjects with definite clinical seizures needed polytherapy (35%). Delayed myelination and/or abnormal white matter hyperintensities were seen on neuroimaging in 19 individuals (61%).

Conclusions: Epileptiform abnormalities are commonly seen in individuals with SATB2-associated syndrome. A baseline electroencephalography that preferably includes sleep stages is recommended during the initial evaluation of all individuals with SATB2-associated syndrome, regardless of clinical suspicion of epilepsy.
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http://dx.doi.org/10.1016/j.pediatrneurol.2020.04.006DOI Listing
November 2020

Randomized Clinical Trial of First-Line Genome Sequencing in Pediatric White Matter Disorders.

Ann Neurol 2020 08 9;88(2):264-273. Epub 2020 Jun 9.

Illumina, San Diego, California, USA.

Objective: Genome sequencing (GS) is promising for unsolved leukodystrophies, but its efficacy has not been prospectively studied.

Methods: A prospective time-delayed crossover design trial of GS to assess the efficacy of GS as a first-line diagnostic tool for genetic white matter disorders took place between December 1, 2015 and September 27, 2017. Patients were randomized to receive GS immediately with concurrent standard of care (SoC) testing, or to receive SoC testing for 4 months followed by GS.

Results: Thirty-four individuals were assessed at interim review. The genetic origin of 2 patient's leukoencephalopathy was resolved before randomization. Nine patients were stratified to the immediate intervention group and 23 patients to the delayed-GS arm. The efficacy of GS was significant relative to SoC in the immediate (5/9 [56%] vs 0/9 [0%]; Wild-Seber, p < 0.005) and delayed (control) arms (14/23 [61%] vs 5/23 [22%]; Wild-Seber, p < 0.005). The time to diagnosis was significantly shorter in the immediate-GS group (log-rank test, p = 0.04). The overall diagnostic efficacy of combined GS and SoC approaches was 26 of 34 (76.5%, 95% confidence interval = 58.8-89.3%) in <4 months, greater than historical norms of <50% over 5 years. Owing to loss of clinical equipoise, the trial design was altered to a single-arm observational study.

Interpretation: In this study, first-line GS provided earlier and greater diagnostic efficacy in white matter disorders. We provide an evidence-based diagnostic testing algorithm to enable appropriate clinical GS utilization in this population. ANN NEUROL 2020;88:264-273.
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http://dx.doi.org/10.1002/ana.25757DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8061316PMC
August 2020

De novo EIF2AK1 and EIF2AK2 Variants Are Associated with Developmental Delay, Leukoencephalopathy, and Neurologic Decompensation.

Am J Hum Genet 2020 04 19;106(4):570-583. Epub 2020 Mar 19.

Stanford Center for Undiagnosed Diseases, Stanford University, Stanford, CA 94305, USA; Department of Pediatrics, Stanford University School of Medicine, Stanford, CA 94305, USA.

EIF2AK1 and EIF2AK2 encode members of the eukaryotic translation initiation factor 2 alpha kinase (EIF2AK) family that inhibits protein synthesis in response to physiologic stress conditions. EIF2AK2 is also involved in innate immune response and the regulation of signal transduction, apoptosis, cell proliferation, and differentiation. Despite these findings, human disorders associated with deleterious variants in EIF2AK1 and EIF2AK2 have not been reported. Here, we describe the identification of nine unrelated individuals with heterozygous de novo missense variants in EIF2AK1 (1/9) or EIF2AK2 (8/9). Features seen in these nine individuals include white matter alterations (9/9), developmental delay (9/9), impaired language (9/9), cognitive impairment (8/9), ataxia (6/9), dysarthria in probands with verbal ability (6/9), hypotonia (7/9), hypertonia (6/9), and involuntary movements (3/9). Individuals with EIF2AK2 variants also exhibit neurological regression in the setting of febrile illness or infection. We use mammalian cell lines and proband-derived fibroblasts to further confirm the pathogenicity of variants in these genes and found reduced kinase activity. EIF2AKs phosphorylate eukaryotic translation initiation factor 2 subunit 1 (EIF2S1, also known as EIF2α), which then inhibits EIF2B activity. Deleterious variants in genes encoding EIF2B proteins cause childhood ataxia with central nervous system hypomyelination/vanishing white matter (CACH/VWM), a leukodystrophy characterized by neurologic regression in the setting of febrile illness and other stressors. Our findings indicate that EIF2AK2 missense variants cause a neurodevelopmental syndrome that may share phenotypic and pathogenic mechanisms with CACH/VWM.
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http://dx.doi.org/10.1016/j.ajhg.2020.02.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7118694PMC
April 2020

Successful liver transplantation in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE).

Mol Genet Metab 2020 05 6;130(1):58-64. Epub 2020 Mar 6.

Department of Pediatrics, Section of Genetics and Metabolism, University of Colorado School of Medicine, Aurora, CO, USA. Electronic address:

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a fatal disorder characterized by progressive gastrointestinal dysmotility, peripheral neuropathy, leukoencephalopathy, skeletal myopathy, ophthalmoparesis, and ptosis. MNGIE stems from deficient thymidine phosphorylase activity (TP) leading to toxic elevations of plasma thymidine. Hematopoietic stem cell transplant (HSCT) restores TP activity and halts disease progression but has high transplant-related morbidity and mortality. Liver transplant (LT) was reported to restore TP activity in two adult MNGIE patients. We report successful LT in four additional MNGIE patients, including a pediatric patient. Our patients were diagnosed between ages 14 months and 36 years with elevated thymidine levels and biallelic pathogenic variants in TYMP. Two patients presented with progressive gastrointestinal dysmotility, and three demonstrated progressive peripheral neuropathy with two suffering limitations in ambulation. Two patients, including the child, had liver dysfunction and cirrhosis. Following LT, thymidine levels nearly normalized in all four patients and remained low for the duration of follow-up. Disease symptoms stabilized in all patients, with some manifesting improvements, including intestinal function. No patient died, and LT appeared to have a more favorable safety profile than HSCT, especially when liver disease is present. Follow-up studies will need to document the long-term impact of this new approach on disease outcome. Take Home Message: Liver transplantation is effective in stabilizing symptoms and nearly normalizing thymidine levels in patients with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and may have an improved safety profile over hematopoietic stem cell transplant.
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http://dx.doi.org/10.1016/j.ymgme.2020.03.001DOI Listing
May 2020

RARS1-related hypomyelinating leukodystrophy: Expanding the spectrum.

Ann Clin Transl Neurol 2020 01 8;7(1):83-93. Epub 2019 Dec 8.

Metabolic Unit, Department of Clinical Chemistry, Amsterdam Neuroscience, Amsterdam Gastroenterology & Metabolism, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.

Objective: Biallelic variants in RARS1, encoding the cytoplasmic tRNA synthetase for arginine (ArgRS), cause a hypomyelinating leukodystrophy. This study aimed to investigate clinical, neuroradiological and genetic features of patients with RARS1-related disease, and to identify possible genotype-phenotype relationships.

Methods: We performed a multinational cross-sectional survey among 20 patients with biallelic RARS1 variants identified by next-generation sequencing techniques. Clinical data, brain MRI findings and genetic results were analyzed. Additionally, ArgRS activity was measured in fibroblasts of four patients, and translation of long and short ArgRS isoforms was quantified by western blot.

Results: Clinical presentation ranged from severe (onset in the first 3 months, usually with refractory epilepsy and early brain atrophy), to intermediate (onset in the first year with nystagmus and spasticity), and mild (onset around or after 12 months with minimal cognitive impairment and preserved independent walking). The most frequent RARS1 variant, c.5A>G, led to mild or intermediate phenotypes, whereas truncating variants and variants affecting amino acids close to the ArgRS active centre led to severe phenotypes. ArgRS activity was significantly reduced in three patients with intermediate and severe phenotypes; in a fourth patient with intermediate to severe presentation, we measured normal ArgRS activity, but found translation mainly of the short instead of the long ArgRS isoform.

Interpretation: Variants in RARS1 impair ArgRS activity and do not only lead to a classic hypomyelination presentation with nystagmus and spasticity, but to a wide spectrum, ranging from severe, early-onset epileptic encephalopathy with brain atrophy to mild disease with relatively preserved myelination.
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http://dx.doi.org/10.1002/acn3.50960DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6952319PMC
January 2020

The Expanding Role of Genetics in Cerebral Palsy.

Phys Med Rehabil Clin N Am 2020 02;31(1):15-24

Division of Neurology and Departmental Neurosciences, Department Pediatrics, Cerebral Palsy Clinic, Baylor College of Medicine, Houston, TX, USA.

Cerebral palsy is a clinical diagnosis of a nonprogressive developmental disorder of motor impairment. The scope of the diagnosis of cerebral palsy has been broadening significantly in recent years to include patients with genetic disorders. This article helps clinicians to determine which patients would benefit from a thorough genetic/metabolic evaluation and helps to delineate an approach for the work-up, with an emphasis on newer technologies and the evolving fields of fetal medicine and genetics. It provides guidance to providers to assist in clarifying an cause for some patient's symptoms.
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http://dx.doi.org/10.1016/j.pmr.2019.09.006DOI Listing
February 2020

Disruptive mutations in TANC2 define a neurodevelopmental syndrome associated with psychiatric disorders.

Nat Commun 2019 10 15;10(1):4679. Epub 2019 Oct 15.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, 77030, USA.

Postsynaptic density (PSD) proteins have been implicated in the pathophysiology of neurodevelopmental and psychiatric disorders. Here, we present detailed clinical and genetic data for 20 patients with likely gene-disrupting mutations in TANC2-whose protein product interacts with multiple PSD proteins. Pediatric patients with disruptive mutations present with autism, intellectual disability, and delayed language and motor development. In addition to a variable degree of epilepsy and facial dysmorphism, we observe a pattern of more complex psychiatric dysfunction or behavioral problems in adult probands or carrier parents. Although this observation requires replication to establish statistical significance, it also suggests that mutations in this gene are associated with a variety of neuropsychiatric disorders consistent with its postsynaptic function. We find that TANC2 is expressed broadly in the human developing brain, especially in excitatory neurons and glial cells, but shows a more restricted pattern in Drosophila glial cells where its disruption affects behavioral outcomes.
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http://dx.doi.org/10.1038/s41467-019-12435-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6794285PMC
October 2019

Loss-of-function mutations in Lysyl-tRNA synthetase cause various leukoencephalopathy phenotypes.

Neurol Genet 2019 Apr 18;5(2):e565. Epub 2019 Apr 18.

Department of Neurology (C.S., J.S., C.Z., J. Lu, J.X., S. Luo, J. Lin), Huashan Hospital, Fudan University, Shanghai, China; Baylor Genetic Laboratories (Y.J., Z.N., M.L.L., M.W., R.E.P., H.M., Y.Y.), Houston, TX; Department of Radiology (Y.L.), Huashan Hospital, Fudan University; Department of Pathology (Y.W., M.G.), Huashan Hospital, Fudan University, Shanghai, China; Department of Biochemistry and Molecular Pharmacology (M.L., K.D., Y.-M.H.), Thomas Jefferson University, Philadelphia, PA; Department of Human Genetics (S.N.O., A.A.), University of Michigan Medical School, Ann Arbor, MI; Department of Pediatrics and Department of Obstetrics and Gynecology (S.L.), University of Hawaii School of Medicine, Honolulu, HI; Department of Medical Oncology and Therapeutics Research (T.P.S.), Division of Clinical Cancer Genetics, City of Hope National Medical Center, Duarte, CA; Department of Molecular and Human Genetics (P.L.M., A.L.M., L.E., S.R.L., Z.N., M.L.L., J.A.R., M.W., R.E.P., H.M., J.A.R., Y.Y., V.W.Z.), Baylor College of Medicine, Houston, TX; and AmCare Genomics Lab (V.W.Z.), Guangzhou, China.

Objective: To expand the clinical spectrum of lysyl-tRNA synthetase () gene-related diseases, which so far includes Charcot-Marie-Tooth disease, congenital visual impairment and microcephaly, and nonsyndromic hearing impairment.

Methods: Whole-exome sequencing was performed on index patients from 4 unrelated families with leukoencephalopathy. Candidate pathogenic variants and their cosegregation were confirmed by Sanger sequencing. Effects of mutations on KARS protein function were examined by aminoacylation assays and yeast complementation assays.

Results: Common clinical features of the patients in this study included impaired cognitive ability, seizure, hypotonia, ataxia, and abnormal brain imaging, suggesting that the CNS involvement is the main clinical presentation. Six previously unreported and 1 known mutations were identified and cosegregated in these families. Two patients are compound heterozygous for missense mutations, 1 patient is homozygous for a missense mutation, and 1 patient harbored an insertion mutation and a missense mutation. Functional and structural analyses revealed that these mutations impair aminoacylation activity of lysyl-tRNA synthetase, indicating that defective KARS function is responsible for the phenotypes in these individuals.

Conclusions: Our results demonstrate that patients with loss-of-function mutations can manifest CNS disorders, thus broadening the phenotypic spectrum associated with KARS-related disease.
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http://dx.doi.org/10.1212/NXG.0000000000000316DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6515944PMC
April 2019

2-Pyrrolidinone and Succinimide as Clinical Screening Biomarkers for GABA-Transaminase Deficiency: Anti-seizure Medications Impact Accurate Diagnosis.

Front Neurosci 2019 8;13:394. Epub 2019 May 8.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States.

Broad-scale untargeted biochemical phenotyping is a technology that supplements widely accepted assays, such as organic acid, amino acid, and acylcarnitine analyses typically utilized for the diagnosis of inborn errors of metabolism. In this study, we investigate the analyte changes associated with 4-aminobutyrate aminotransferase (ABAT, GABA transaminase) deficiency and treatments that affect GABA metabolism. GABA-transaminase deficiency is a rare neurodevelopmental and neurometabolic disorder caused by mutations in and resulting in accumulation of GABA in the cerebrospinal fluid (CSF). For that reason, measurement of GABA in CSF is currently the primary approach to diagnosis. GABA-transaminase deficiency results in severe developmental delay with intellectual disability, seizures, and movement disorder, and is often associated with death in childhood. Using an untargeted metabolomics platform, we analyzed EDTA plasma, urine, and CSF specimens from four individuals with GABA-transaminase deficiency to identify biomarkers by comparing the biochemical profile of individual patient samples to a pediatric-centric population cohort. Metabolomic analyses of over 1,000 clinical plasma samples revealed a rich source of biochemical information. Three out of four patients showed significantly elevated levels of the molecule 2-pyrrolidinone (-score ≥2) in plasma, and whole exome sequencing revealed variants of uncertain significance in . Additionally, these same patients also had elevated levels of succinimide in plasma, urine, and CSF and/or homocarnosine in urine and CSF. In the analysis of clinical EDTA plasma samples, the levels of succinimide and 2-pyrrolidinone showed a high level of correlation ( = 0.73), indicating impairment in GABA metabolism and further supporting the association with GABA-transaminase deficiency and the pathogenicity of the variants. Further analysis of metabolomic data across our patient population revealed the association of elevated levels of 2-pyrrolidinone with administration of vigabatrin, a commonly used anti-seizure medication and a known inhibitor of GABA-transaminase. These data indicate that anti-seizure medications may alter the biochemical and metabolomic data, potentially impacting the interpretation and diagnosis for the patient. Further, these data demonstrate the power of combining broad scale genotyping and phenotyping technologies to diagnose inherited neurometabolic disorders and support the use of metabolic phenotyping of plasma to screen for GABA-transaminase deficiency.
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http://dx.doi.org/10.3389/fnins.2019.00394DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6517487PMC
May 2019

Early Identification of Pediatric Neurology Patients With Palliative Care Needs: A Pilot Study.

Am J Hosp Palliat Care 2019 Nov 23;36(11):959-966. Epub 2019 Apr 23.

4 Section of Palliative Medicine, Department of Pediatrics, Baylor College of Medicine, Texas Children's Hospital, Houston, TX, USA.

Palliative care services are beneficial for pediatric neurology patients with chronic, life-limiting illnesses. However, timely referral to palliative care may be impeded due to an inability to identify appropriate patients. The aim of this pilot case-control study was to test a quantitative measure for identifying patients with unmet palliative care needs to facilitate appropriate referrals. First, a random subset of pediatric neurology patients were screened for number of hospital admissions, emergency center visits, and problems on the problem list. Screening results led to the hypothesis that having six or more hospital admissions in one year indicated unmet palliative care needs. Next, hospital admissions in the past year were counted for all patients admitted to the neurology service during a six-month period. Patients with six or more admissions as well as age- and gender-matched controls were assessed for unmet palliative care needs. In hospitalized pediatric neurology patients, having six or more admissions in the preceding year did not predict unmet palliative care needs. While this pilot study did not find a quantitative measure that identifies patients needing a palliative care consultation, the negative finding highlights an important distinction between unmet social needs that interfere with care and unmet palliative care needs. Further, the method of screening patients used in this study was simple to implement and provides a framework for future studies.
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http://dx.doi.org/10.1177/1049909119844519DOI Listing
November 2019

Bi-allelic Variants in TONSL Cause SPONASTRIME Dysplasia and a Spectrum of Skeletal Dysplasia Phenotypes.

Am J Hum Genet 2019 03 14;104(3):422-438. Epub 2019 Feb 14.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.

SPONASTRIME dysplasia is an autosomal-recessive spondyloepimetaphyseal dysplasia characterized by spine (spondylar) abnormalities, midface hypoplasia with a depressed nasal bridge, metaphyseal striations, and disproportionate short stature. Scoliosis, coxa vara, childhood cataracts, short dental roots, and hypogammaglobulinemia have also been reported in this disorder. Although an autosomal-recessive inheritance pattern has been hypothesized, pathogenic variants in a specific gene have not been discovered in individuals with SPONASTRIME dysplasia. Here, we identified bi-allelic variants in TONSL, which encodes the Tonsoku-like DNA repair protein, in nine subjects (from eight families) with SPONASTRIME dysplasia, and four subjects (from three families) with short stature of varied severity and spondylometaphyseal dysplasia with or without immunologic and hematologic abnormalities, but no definitive metaphyseal striations at diagnosis. The finding of early embryonic lethality in a Tonsl murine model and the discovery of reduced length, spinal abnormalities, reduced numbers of neutrophils, and early lethality in a tonsl zebrafish model both support the hypomorphic nature of the identified TONSL variants. Moreover, functional studies revealed increased amounts of spontaneous replication fork stalling and chromosomal aberrations, as well as fewer camptothecin (CPT)-induced RAD51 foci in subject-derived cell lines. Importantly, these cellular defects were rescued upon re-expression of wild-type (WT) TONSL; this rescue is consistent with the hypothesis that hypomorphic TONSL variants are pathogenic. Overall, our studies in humans, mice, zebrafish, and subject-derived cell lines confirm that pathogenic variants in TONSL impair DNA replication and homologous recombination-dependent repair processes, and they lead to a spectrum of skeletal dysplasia phenotypes with numerous extra-skeletal manifestations.
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http://dx.doi.org/10.1016/j.ajhg.2019.01.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6408318PMC
March 2019

Recurrent mosaic MTOR c.5930C > T (p.Thr1977Ile) variant causing megalencephaly, asymmetric polymicrogyria, and cutaneous pigmentary mosaicism: Case report and review of the literature.

Am J Med Genet A 2019 03 19;179(3):475-479. Epub 2018 Dec 19.

Department of Pediatrics, Section of Neurology and Developmental Neuroscience, Baylor College of Medicine, Houston, Texas.

Genetic alterations leading to overactivation of mammalian target of rapamycin (mTOR) signaling result in brain overgrowth syndromes such as focal cortical dysplasia (FCD) and megalencephaly. Megalencephaly with cutis tri-color of the Blaschko-linear type pigmentary mosaicism and intellectual disability is a rare neurodevelopmental disorder attributed to the recurrent mosaic c.5930C > T (p.Thr1977Ile) MTOR variant. This variant was previously reported at low to intermediate levels of mosaicism in the peripheral blood of three unrelated individuals with consistent clinical findings. We report a fourth case of a 3-year-old female presenting with megalencephaly, obstructive hydrocephalus due to cerebral aqueductal stenosis, asymmetric polymicrogyria, dysgenesis of the corpus callosum, hypotonia, developmental delay, and cutaneous pigmentary mosaicism. Oligonucleotide and SNP chromosomal microarray (CMA), karyotype, and trio whole exome sequencing (WES) in the peripheral blood, as well as a targeted gene variant panel from fibroblasts derived from hyperpigmented and non-hyperpigmented skin did not detect any abnormalities in MTOR or other genes associated with brain overgrowth syndromes. Unlike the previously reported cases, the de novo c.5930C > T (p.Thr1977Ile) MTOR variant was detected at 32% mosaicism in our patient only after WES was performed on fibroblast-derived DNA from the hyperpigmented skin. This case demonstrates the tissue variability in mosaic expression of the recurrent p.Thr1977Ile MTOR variant, emphasizes the need for skin biopsies in the genetic evaluation of patients with skin pigmentary mosaicism, and expands the clinical phenotype associated with this pathogenic MTOR variant.
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http://dx.doi.org/10.1002/ajmg.a.61007DOI Listing
March 2019

Microdeletions excluding YWHAE and PAFAH1B1 cause a unique leukoencephalopathy: further delineation of the 17p13.3 microdeletion spectrum.

Genet Med 2019 07 20;21(7):1652-1656. Epub 2018 Dec 20.

Department of Pediatrics, Baylor College of Medicine, Houston, TX, USA.

Purpose: Brain malformations caused by 17p13.3 deletions include lissencephaly with deletions of the larger Miller-Dieker syndrome region or smaller deletions of only PAFAH1B1, white matter changes, and a distinct syndrome due to deletions including YWHAE and CRK but sparing PAFAH1B1. We sought to understand the significance of 17p13.3 deletions between the YWHAE/CRK and PAFAH1B1 loci.

Methods: We analyzed the clinical features of six individuals from five families with 17p13.3 deletions between and not including YWHAE/CRK and PAFAH1B1 identified among individuals undergoing clinical chromosomal microarray testing or research genome sequencing.

Results: Five individuals from four families had multifocal white matter lesions while a sixth had a normal magnetic resonance image. A combination of our individuals and a review of those in the literature with white matter changes and deletions in this chromosomal region narrows the overlapping region for this brain phenotype to ~345 kb, including 11 RefSeq genes, with RTN4RL1 haploinsufficiency as the best candidate for causing this phenotype.

Conclusion: While previous literature has hypothesized dysmorphic features and white matter changes related to YWHAE, our cohort contributes evidence to the presence of additional genetic changes within 17p13.3 required for proper brain development.
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http://dx.doi.org/10.1038/s41436-018-0358-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6586530PMC
July 2019

Pathogenic Variants in Fucokinase Cause a Congenital Disorder of Glycosylation.

Am J Hum Genet 2018 12 29;103(6):1030-1037. Epub 2018 Nov 29.

Human Genetics Program, Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, CA 92037, USA. Electronic address:

FUK encodes fucokinase, the only enzyme capable of converting L-fucose to fucose-1-phosphate, which will ultimately be used for synthesizing GDP-fucose, the donor substrate for all fucosyltransferases. Although it is essential for fucose salvage, this pathway is thought to make only a minor contribution to the total amount of GDP-fucose. A second pathway, the major de novo pathway, involves conversion of GDP-mannose to GDP-fucose. Here we describe two unrelated individuals who have pathogenic variants in FUK and who presented with severe developmental delays, encephalopathy, intractable seizures, and hypotonia. The first individual was compound heterozygous for c.667T>C (p.Ser223Pro) and c.2047C>T (p.Arg683Cys), and the second individual was homozygous for c.2980A>C (p.Lys994Gln). Skin fibroblasts from the first individual confirmed the variants as loss of function and showed significant decreases in total GDP-[H] fucose and [H] fucose-1-phosphate. There was also a decrease in the incorporation of [5,6-H]-fucose into fucosylated glycoproteins. Lys994 has previously been shown to be an important site for ubiquitin conjugation. Here, we show that loss-of-function variants in FUK cause a congenital glycosylation disorder characterized by a defective fucose-salvage pathway.
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http://dx.doi.org/10.1016/j.ajhg.2018.10.021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6288200PMC
December 2018

Clinical Reasoning: Ventriculomegaly detected on 20-week anatomic fetal ultrasound.

Neurology 2018 09;91(13):e1265-e1268

From the Department of Pediatrics, Section of Neurology and Developmental Neuroscience (R.C.S., A.M.L.-W., L.E.), and Department of Molecular and Human Genetics (L.E.), Baylor College of Medicine, Texas Children's Hospital, Houston.

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http://dx.doi.org/10.1212/WNL.0000000000006247DOI Listing
September 2018

Heterozygous Truncating Variants in POMP Escape Nonsense-Mediated Decay and Cause a Unique Immune Dysregulatory Syndrome.

Am J Hum Genet 2018 06 24;102(6):1126-1142. Epub 2018 May 24.

Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA; Texas Children's Hospital, Division of Pediatric Immunology, Allergy, and Rheumatology, Houston, TX 77030, USA. Electronic address:

The proteasome processes proteins to facilitate immune recognition and host defense. When inherently defective, it can lead to aberrant immunity resulting in a dysregulated response that can cause autoimmunity and/or autoinflammation. Biallelic or digenic loss-of-function variants in some of the proteasome subunits have been described as causing a primary immunodeficiency disease that manifests as a severe dysregulatory syndrome: chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE). Proteasome maturation protein (POMP) is a chaperone for proteasome assembly and is critical for the incorporation of catalytic subunits into the proteasome. Here, we characterize and describe POMP-related autoinflammation and immune dysregulation disease (PRAID) discovered in two unrelated individuals with a unique constellation of early-onset combined immunodeficiency, inflammatory neutrophilic dermatosis, and autoimmunity. We also begin to delineate a complex genetic mechanism whereby de novo heterozygous frameshift variants in the penultimate exon of POMP escape nonsense-mediated mRNA decay (NMD) and result in a truncated protein that perturbs proteasome assembly by a dominant-negative mechanism. To our knowledge, this mechanism has not been reported in any primary immunodeficiencies, autoinflammatory syndromes, or autoimmune diseases. Here, we define a unique hypo- and hyper-immune phenotype and report an immune dysregulation syndrome caused by frameshift mutations that escape NMD.
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http://dx.doi.org/10.1016/j.ajhg.2018.04.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5992134PMC
June 2018

Autosomal recessive Noonan syndrome associated with biallelic LZTR1 variants.

Genet Med 2018 10 22;20(10):1175-1185. Epub 2018 Feb 22.

National Institute for Health Research Oxford Biomedical Research Centre, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK.

Purpose: To characterize the molecular genetics of autosomal recessive Noonan syndrome.

Methods: Families underwent phenotyping for features of Noonan syndrome in children and their parents. Two multiplex families underwent linkage analysis. Exome, genome, or multigene panel sequencing was used to identify variants. The molecular consequences of observed splice variants were evaluated by reverse-transcription polymerase chain reaction.

Results: Twelve families with a total of 23 affected children with features of Noonan syndrome were evaluated. The phenotypic range included mildly affected patients, but it was lethal in some, with cardiac disease and leukemia. All of the parents were unaffected. Linkage analysis using a recessive model supported a candidate region in chromosome 22q11, which includes LZTR1, previously shown to harbor mutations in patients with Noonan syndrome inherited in a dominant pattern. Sequencing analyses of 21 live-born patients and a stillbirth identified biallelic pathogenic variants in LZTR1, including putative loss-of-function, missense, and canonical and noncanonical splicing variants in the affected children, with heterozygous, clinically unaffected parents and heterozygous or normal genotypes in unaffected siblings.

Conclusion: These clinical and genetic data confirm the existence of a form of Noonan syndrome that is inherited in an autosomal recessive pattern and identify biallelic mutations in LZTR1.
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http://dx.doi.org/10.1038/gim.2017.249DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6105555PMC
October 2018

Identification of novel candidate disease genes from de novo exonic copy number variants.

Genome Med 2017 09 21;9(1):83. Epub 2017 Sep 21.

St. Luke's Children's Hospital, Boise, ID, 83702, USA.

Background: Exon-targeted microarrays can detect small (<1000 bp) intragenic copy number variants (CNVs), including those that affect only a single exon. This genome-wide high-sensitivity approach increases the molecular diagnosis for conditions with known disease-associated genes, enables better genotype-phenotype correlations, and facilitates variant allele detection allowing novel disease gene discovery.

Methods: We retrospectively analyzed data from 63,127 patients referred for clinical chromosomal microarray analysis (CMA) at Baylor Genetics laboratories, including 46,755 individuals tested using exon-targeted arrays, from 2007 to 2017. Small CNVs harboring a single gene or two to five non-disease-associated genes were identified; the genes involved were evaluated for a potential disease association.

Results: In this clinical population, among rare CNVs involving any single gene reported in 7200 patients (11%), we identified 145 de novo autosomal CNVs (117 losses and 28 intragenic gains), 257 X-linked deletion CNVs in males, and 1049 inherited autosomal CNVs (878 losses and 171 intragenic gains); 111 known disease genes were potentially disrupted by de novo autosomal or X-linked (in males) single-gene CNVs. Ninety-one genes, either recently proposed as candidate disease genes or not yet associated with diseases, were disrupted by 147 single-gene CNVs, including 37 de novo deletions and ten de novo intragenic duplications on autosomes and 100 X-linked CNVs in males. Clinical features in individuals with de novo or X-linked CNVs encompassing at most five genes (224 bp to 1.6 Mb in size) were compared to those in individuals with larger-sized deletions (up to 5 Mb in size) in the internal CMA database or loss-of-function single nucleotide variants (SNVs) detected by clinical or research whole-exome sequencing (WES). This enabled the identification of recently published genes (BPTF, NONO, PSMD12, TANGO2, and TRIP12), novel candidate disease genes (ARGLU1 and STK3), and further confirmation of disease association for two recently proposed disease genes (MEIS2 and PTCHD1). Notably, exon-targeted CMA detected several pathogenic single-exon CNVs missed by clinical WES analyses.

Conclusions: Together, these data document the efficacy of exon-targeted CMA for detection of genic and exonic CNVs, complementing and extending WES in clinical diagnostics, and the potential for discovery of novel disease genes by genome-wide assay.
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http://dx.doi.org/10.1186/s13073-017-0472-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5607840PMC
September 2017

Phenotypic and molecular characterisation of CDK13-related congenital heart defects, dysmorphic facial features and intellectual developmental disorders.

Genome Med 2017 08 14;9(1):73. Epub 2017 Aug 14.

Department of Molecular and Human Genetics, Baylor College of Medicine, 6701 Fannin St, Suite 1560, Houston, TX, 77030, USA.

Background: De novo missense variants in CDK13 have been described as the cause of syndromic congenital heart defects in seven individuals ascertained from a large congenital cardiovascular malformations cohort. We aimed to further define the phenotypic and molecular spectrum of this newly described disorder.

Methods: To minimise ascertainment bias, we recruited nine additional individuals with CDK13 pathogenic variants from clinical and research exome laboratory sequencing cohorts. Each individual underwent dysmorphology exam and comprehensive medical history review.

Results: We demonstrate greater than expected phenotypic heterogeneity, including 33% (3/9) of individuals without structural heart disease on echocardiogram. There was a high penetrance for a unique constellation of facial dysmorphism and global developmental delay, as well as less frequently seen renal and sacral anomalies. Two individuals had novel CDK13 variants (p.Asn842Asp, p.Lys734Glu), while the remaining seven unrelated individuals had a recurrent, previously published p.Asn842Ser variant. Summary of all variants published to date demonstrates apparent restriction of pathogenic variants to the protein kinase domain with clustering in the ATP and magnesium binding sites.

Conclusions: Here we provide detailed phenotypic and molecular characterisation of individuals with pathogenic variants in CDK13 and propose management guidelines based upon the estimated prevalence of anomalies identified.
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http://dx.doi.org/10.1186/s13073-017-0463-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5557075PMC
August 2017

Clinically severe CACNA1A alleles affect synaptic function and neurodegeneration differentially.

PLoS Genet 2017 Jul 24;13(7):e1006905. Epub 2017 Jul 24.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States of America.

Dominant mutations in CACNA1A, encoding the α-1A subunit of the neuronal P/Q type voltage-dependent Ca2+ channel, can cause diverse neurological phenotypes. Rare cases of markedly severe early onset developmental delay and congenital ataxia can be due to de novo CACNA1A missense alleles, with variants affecting the S4 transmembrane segments of the channel, some of which are reported to be loss-of-function. Exome sequencing in five individuals with severe early onset ataxia identified one novel variant (p.R1673P), in a girl with global developmental delay and progressive cerebellar atrophy, and a recurrent, de novo p.R1664Q variant, in four individuals with global developmental delay, hypotonia, and ophthalmologic abnormalities. Given the severity of these phenotypes we explored their functional impact in Drosophila. We previously generated null and partial loss-of-function alleles of cac, the homolog of CACNA1A in Drosophila. Here, we created transgenic wild type and mutant genomic rescue constructs with the two noted conserved point mutations. The p.R1673P mutant failed to rescue cac lethality, displayed a gain-of-function phenotype in electroretinograms (ERG) recorded from mutant clones, and evolved a neurodegenerative phenotype in aging flies, based on ERGs and transmission electron microscopy. In contrast, the p.R1664Q variant exhibited loss of function and failed to develop a neurodegenerative phenotype. Hence, the novel R1673P allele produces neurodegenerative phenotypes in flies and human, likely due to a toxic gain of function.
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http://dx.doi.org/10.1371/journal.pgen.1006905DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5557584PMC
July 2017

Common data elements for clinical research in mitochondrial disease: a National Institute for Neurological Disorders and Stroke project.

J Inherit Metab Dis 2017 05 16;40(3):403-414. Epub 2017 Mar 16.

Children's Hospital of Pittsburgh, 4401 Penn Avenue, Pittsburgh, PA, 15224, USA.

Objectives: The common data elements (CDE) project was developed by the National Institute of Neurological Disorders and Stroke (NINDS) to provide clinical researchers with tools to improve data quality and allow for harmonization of data collected in different research studies. CDEs have been created for several neurological diseases; the aim of this project was to develop CDEs specifically curated for mitochondrial disease (Mito) to enhance clinical research.

Methods: Nine working groups (WGs), composed of international mitochondrial disease experts, provided recommendations for Mito clinical research. They initially reviewed existing NINDS CDEs and instruments, and developed new data elements or instruments when needed. Recommendations were organized, internally reviewed by the Mito WGs, and posted online for external public comment for a period of eight weeks. The final version was again reviewed by all WGs and the NINDS CDE team prior to posting for public use.

Results: The NINDS Mito CDEs and supporting documents are publicly available on the NINDS CDE website ( https://commondataelements.ninds.nih.gov/ ), organized into domain categories such as Participant/Subject Characteristics, Assessments, and Examinations.

Conclusion: We developed a comprehensive set of CDE recommendations, data definitions, case report forms (CRFs), and guidelines for use in Mito clinical research. The widespread use of CDEs is intended to enhance Mito clinical research endeavors, including natural history studies, clinical trial design, and data sharing. Ongoing international collaboration will facilitate regular review, updates and online publication of Mito CDEs, and support improved consistency of data collection and reporting.
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http://dx.doi.org/10.1007/s10545-017-0035-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7783474PMC
May 2017

Diagnosis of adenylosuccinate lyase deficiency by metabolomic profiling in plasma reveals a phenotypic spectrum.

Mol Genet Metab Rep 2016 Sep 27;8:61-6. Epub 2016 Jul 27.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States.

Adenylosuccinate lyase (ADSL) deficiency is a rare autosomal recessive neurometabolic disorder that presents with a broad-spectrum of neurological and physiological symptoms. The ADSL gene produces an enzyme with binary molecular roles in de novo purine synthesis and purine nucleotide recycling. The biochemical phenotype of ADSL deficiency, accumulation of SAICAr and succinyladenosine (S-Ado) in biofluids of affected individuals, serves as the traditional target for diagnosis with targeted quantitative urine purine analysis employed as the predominate method of detection. In this study, we report the diagnosis of ADSL deficiency using an alternative method, untargeted metabolomic profiling, an analytical scheme capable of generating semi-quantitative z-score values for over 1000 unique compounds in a single analysis of a specimen. Using this method to analyze plasma, we diagnosed ADSL deficiency in four patients and confirmed these findings with targeted quantitative biochemical analysis and molecular genetic testing. ADSL deficiency is part of a large a group of neurometabolic disorders, with a wide range of severity and sharing a broad differential diagnosis. This phenotypic similarity among these many inborn errors of metabolism (IEMs) has classically stood as a hurdle in their initial diagnosis and subsequent treatment. The findings presented here demonstrate the clinical utility of metabolomic profiling in the diagnosis of ADSL deficiency and highlights the potential of this technology in the diagnostic evaluation of individuals with neurologic phenotypes.
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http://dx.doi.org/10.1016/j.ymgmr.2016.07.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4969260PMC
September 2016

Recommendations for the Management of Strokelike Episodes in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Strokelike Episodes.

JAMA Neurol 2016 May;73(5):591-4

Department of Pediatrics, Children's Hospital of Pittsburgh of University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania.

Importance: Strokelike episodes are a cardinal feature of several mitochondrial syndromes, including mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS). Recent advances in the understanding of the pathophysiologic mechanisms of strokelike episodes in MELAS have led to improved treatment options.

Observations: Current understanding of the cause of strokelike episodes in MELAS and present recommendations to assist in the identification and treatment of patients with MELAS who present with stroke are presented. Mounting evidence points toward a benefit of the nitric oxide precursors, arginine, to both prevent and reduce the severity of strokes in patients with MELAS.

Conclusions And Relevance: Although much information is still needed regarding the appropriate dosing and timing of arginine therapy in patients with MELAS, urgent administration of nitric oxide precursors in patients with MELAS ameliorates the clinical symptoms associated with strokelike episodes.
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http://dx.doi.org/10.1001/jamaneurol.2015.5072DOI Listing
May 2016

De Novo Mutations in Patients with Ataxic CP.

Pediatr Neurol Briefs 2015 Aug;29(8):62

Departments of Neurology and Developmental Neuroscience, Baylor College of Medicine, Houston, TX.

As a part of a large study investigating childhood ataxias in the UK and Switzerland, Schnekenberg et al. analyzed the genetic associations with congenital cerebellar ataxia in 10 patients using either a targeted next generation sequencing panel of 118 genes or trio-based exome sequencing.
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http://dx.doi.org/10.15844/pedneurbriefs-29-8-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4747133PMC
August 2015

Impaired nitric oxide production in children with MELAS syndrome and the effect of arginine and citrulline supplementation.

Mol Genet Metab 2016 Apr 27;117(4):407-12. Epub 2016 Jan 27.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA; Texas Children's Hospital, Houston, TX, USA. Electronic address:

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is one of the most frequent maternally inherited mitochondrial disorders. The pathogenesis of this syndrome is not fully understood and believed to result from several interacting mechanisms including impaired mitochondrial energy production, microvasculature angiopathy, and nitric oxide (NO) deficiency. NO deficiency in MELAS syndrome is likely to be multifactorial in origin with the decreased availability of the NO precursors, arginine and citrulline, playing a major role. In this study we used stable isotope infusion techniques to assess NO production in children with MELAS syndrome and healthy pediatric controls. We also assessed the effect of oral arginine and citrulline supplementations on NO production in children with MELAS syndrome. When compared to control subjects, children with MELAS syndrome were found to have lower NO production, arginine flux, plasma arginine, and citrulline flux. In children with MELAS syndrome, arginine supplementation resulted in increased NO production, arginine flux, and arginine concentration. Citrulline supplementation resulted in a greater increase of these parameters. Additionally, citrulline supplementation was associated with a robust increase in citrulline concentration and flux and de novo arginine synthesis rate. The greater effect of citrulline in increasing NO production is due to its greater ability to increase arginine availability particularly in the intracellular compartment in which NO synthesis takes place. This study, which is the first one to assess NO metabolism in children with mitochondrial diseases, adds more evidence to the notion that NO deficiency occurs in MELAS syndrome, suggests a better effect for citrulline because of its greater role as NO precursor, and indicates that impaired NO production occurs in children as well as adults with MELAS syndrome. Thus, the initiation of treatment with NO precursors may be beneficial earlier in life. Controlled clinical trials to assess the therapeutic effects of arginine and citrulline on clinical complications of MELAS syndrome are needed.
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http://dx.doi.org/10.1016/j.ymgme.2016.01.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4818739PMC
April 2016