De novo missense variants in exon 9 of SEPHS1 cause a neurodevelopmental condition with developmental delay, poor growth, hypotonia, and dysmorphic features.

Selenophosphate synthetase (SEPHS) plays an essential role in selenium metabolism. Two mammalian SEPHS paralogues, SEPHS1 and SEPHS2, share high sequence identity and structural homology with SEPHS. Here, we report nine individuals from eight families with developmental delay, growth and feeding problems, hypotonia, and dysmorphic features, all with heterozygous missense variants in SEPHS1. Eight of these individuals had a recurrent variant at amino acid position 371 of SEPHS1 (p.Arg371Trp, p.Arg371Gln, and p.Arg371Gly); seven of these variants were known to be de novo. Structural modeling and biochemical assays were used to understand the effect of these variants on SEPHS1 function. We found that a variant at residue Trp352 results in local structural changes of the C-terminal region of SEPHS1 that decrease the overall thermal stability of the enzyme. In contrast, variants of a solvent-exposed residue Arg371 do not impact enzyme stability and folding but could modulate direct protein-protein interactions of SEPSH1 with cellular factors in promoting cell proliferation and development. In neuronal SH-SY5Y cells, we assessed the impact of SEPHS1 variants on cell proliferation and ROS production and investigated the mRNA expression levels of genes encoding stress-related selenoproteins. Our findings provided evidence that the identified SEPHS1 variants enhance cell proliferation by modulating ROS homeostasis. Our study supports the hypothesis that SEPHS1 plays a critical role during human development and provides a basis for further investigation into the molecular mechanisms employed by SEPHS1. Furthermore, our data suggest that variants in SEPHS1 are associated with a neurodevelopmental disorder.

Clinical manifestations and management of fatty acid oxidation disorders.

Fatty acid oxidation disorders (FAOD) are a group of rare, autosomal recessive, metabolic disorders caused by variants of the genes for the enzymes and proteins involved in the transport and metabolism of fatty acids in the mitochondria. Those affected by FAOD are unable to convert fatty acids into tricarboxylic acid cycle intermediates such as acetyl-coenzyme A, resulting in decreased adenosine triphosphate and glucose for use as energy in a variety of high-energy-requiring organ systems. Signs and symptoms may manifest in infants but often also appear in adolescents or adults during times of increased metabolic demand, such as fasting, physiologic stress, and prolonged exercise. Patients with FAOD present with a highly heterogeneous clinical spectrum. The most common clinical presentations include hypoketotic hypoglycemia, liver dysfunction, cardiomyopathy, rhabdomyolysis, and skeletal myopathy, as well as peripheral neuropathy and retinopathy in some subtypes. Despite efforts to detect FAOD through newborn screening and manage patients early, symptom onset can be sudden and serious, even resulting in death. Therefore, it is critical to identify quickly and accurately the key signs and symptoms of patients with FAOD to manage metabolic decompensations and prevent serious comorbidities.

Self-reported treatment-associated symptoms among patients with urea cycle disorders participating in glycerol phenylbutyrate clinical trials.

BACKGROUND: Health care outcomes have been increasingly assessed through health-related quality of life (HRQoL) measures. While the introduction of nitrogen-scavenging medications has improved survival in patients with urea cycle disorders (UCDs), they are often associated with side effects that may affect patient compliance and outcomes. METHODS: Symptoms commonly associated with nitrogen-scavenging medications were evaluated in 100 adult and pediatric participants using a non-validated UCD-specific questionnaire. Patients or their caregivers responded to a pre-defined list of symptoms known to be associated with the use of these medications. Responses were collected at baseline (while patients were receiving sodium phenylbutyrate [NaPBA]) and during treatment with glycerol phenylbutyrate (GPB). RESULTS: After 3 months of GPB dosing, there were significant reductions in the proportion of patients with treatment-associated symptoms (69% vs. 46%; p<0.0001), the number of symptoms per patient (2.5 vs. 1.1; p<0.0001), and frequency of the more commonly reported individual symptoms such as body odor, abdominal pain, nausea, burning sensation in mouth, vomiting, and heartburn (p<0.05). The reduction in symptoms was observed in both pediatric and adult patients. The presence or absence of symptoms or change in severity did not correlate with plasma ammonia levels or NaPBA dose. CONCLUSIONS: The reduction in symptoms following 3 months of open-label GPB dosing was similar in pediatric and adult patients and may be related to chemical structure and intrinsic characteristics of the product rather than its effect on ammonia control.

Infants suspected to have very-long chain acyl-CoA dehydrogenase deficiency from newborn screening.

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a fatty acid oxidation disorder with widely varying presentations that has presented a significant challenge to newborn screening (NBS). The Western States Regional Genetics Services Collaborative developed a workgroup to study infants with NBS positive for VLCADD. We performed retrospective analysis of newborns with elevated C14:1-acylcarnitine on NBS in California, Oregon, Washington, and Hawai'i including available confirmatory testing and clinical information. Overall, from 2,802,504 children screened, there were 242 cases screen-positive for VLCADD. There were 34 symptomatic true positive cases, 18 asymptomatic true positives, 112 false positives, 55 heterozygotes, 11 lost to follow-up, and 12 other disorders. One in 11,581 newborns had an abnormal NBS for suspected VLCADD. Comparison of analytes and analyte ratios from the NBS demonstrated statistically significant differences between true positive and false positive groups for C14:1, C14, C14:1/C2, and C14:1/C16. The positive predictive value for all true positive cases was 94%, 54%, and 23% when C14:1 was ≥2.0 µM, ≥1.0 µM, and ≥0.7 µM, respectively. Sequential post-analytical analysis could reduce the referral rate in 25.8% of cases. This study is the largest reported follow-up of infants with NBS screen-positive results for suspected VLCADD and demonstrates the necessity of developing comprehensive and consistent long-term follow-up NBS systems. Application of clinical information revealed differences between symptomatic and asymptomatic children with VLCADD. Comparison of NBS analytes and analyte ratios may be valuable in developing more effective diagnostic algorithms.

Cystathionine beta-synthase deficiency heralded by cerebral sinus venous thrombosis and stroke.

BACKGROUND: Elevated plasma homocysteine is a risk factor for arterial and venous thromboses in adults. Homocysteine is increased in cystathionine beta-synthase deficiency, a treatable amino acid metabolic disorder that may be missed on newborn screening placing children at risk of thrombosis and strokes. PATIENT: We present a 3-year-old girl with normal newborn screening for cystathionine beta-synthase deficiency who developed a symptomatic cerebral venous sinus thrombosis. Subsequent testing revealed marked hyperhomocystinemia and genetic testing confirmed cystathionine beta-synthase deficiency. CONCLUSIONS: Current newborn screening is limited in its ability to detect cystathionine beta-synthase deficiency and although postanalytical interpretation may provide increased sensitivity, a normal newborn screening result should not replace the importance of physician surveillance.

Next-generation sequencing for mitochondrial diseases: a wide diagnostic spectrum.

BACKGROUND: The current diagnostic approach for mitochondrial disorders requires invasive procedures such as muscle biopsy and multiple biochemical testing but the results are often inconclusive. Clinical sequencing tests are available only for a limited number of genes. Recently, massively parallel sequencing has become a powerful tool for testing genetically heterogeneous conditions such as mitochondrial disorders. METHODS: Targeted next-generation sequencing was performed on 26 patients with known or suspected mitochondrial disorders using in-solution capture for the exons of 908 known and candidate nuclear genes and an Illumina genome analyzer. RESULTS: None of the 18 patients with various abnormal respiratory chain complex (RCC) activities had molecular defects in either subunits or assembly factors of mitochondrial RCC enzymes except a reference control sample with known mutations in SURF1. Instead, several variants in known pathogenic genes including CPT2, POLG, PDSS1, UBE3A, SDHD, and a few potentially pathogenic variants in candidate genes such as MTO1 or SCL7A13 were identified. CONCLUSIONS: Sequencing only nuclear genes for RCC subunits and assembly factors may not provide the diagnostic answers for suspected patients with mitochondrial disorders. The present findings indicate that the diagnostic spectrum of mitochondrial disorders is much broader than previously thought, which could potentially lead to misdiagnosis and/or inappropriate treatment. Overall analytic sensitivity and precision appear acceptable for clinical testing. Despite the limitations in finding mutations in all patients, the present findings underscore the considerable clinical benefits of targeted next-generation sequencing and serve as a prototype for extending the clinical evaluation in this clinically heterogeneous patient group.

Biochemical correction of very long-chain acyl-CoA dehydrogenase deficiency following adeno-associated virus gene therapy.

We report the development of a gene replacement strategy for very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. VLCAD is a mitochondrial enzyme involved in fatty acid beta-oxidation, a key step in energy production during times of fasting or stress. Deficiency of VLCAD classically presents as hepatic dysfunction, hypoglycemia, cardiomyopathy, rhabdomyolysis, and/or sudden death. While dietary therapy for VLCAD deficiency has proven beneficial in preventing some symptoms, a risk of metabolic catastrophic decompensation remains throughout life during times of increased energy demand. We designed a recombinant adeno-associated virus (AAV) expressing the human VLCAD gene (AAV8-hVLCAD). To demonstrate its in vivo activity, AAV8-hVLCAD was administered via the tail vein to VLCAD-knockout mice. A reduction in accumulated serum long-chain acylcarnitines and increased fasting tolerance judged on blood glucose concentrations were observed as of 11 days postinjections through >100 days. Western analysis of liver, skeletal muscle, and heart extracts using PEP1 anti-hVLCAD antibody revealed short-term hVLCAD expression in the liver and muscle and longer-term expression in heart. This demonstrates the ability of human VLCAD to correct the biochemical phenotype of VLCAD-deficient mice.

Ornithine transcarbamylase deficiency presenting as encephalopathy during adulthood following bariatric surgery.

BACKGROUND: Neurological complications following bariatric surgery are rare. Whereas nutritional deficiencies are the most common cause of neurological symptoms, the unmasking of previously subclinical metabolic disorders can also lead to significant morbidity. OBJECTIVE: To characterize the clinical presentation, serum biochemical fluctuations, and functional enzymatic analysis of a case of functional ornithine transcarbamylase deficiency unmasked by a dietary change following bariatric surgery. DESIGN: Case report. SETTING: Tertiary referral center, hospital (inpatient) setting. PATIENT: A 29-year-old woman who presented with intermittent encephalopathy associated with recurrent hyperammonemia. INTERVENTIONS: Clinical, biochemical, and mutational studies. RESULTS: The pattern of intermittent hyperammonemia and encephalopathy following oral and parenteral nutrition suggested a urea cycle abnormality. Functional enzymatic assay results showed markedly reduced ornithine transcarbamylase activity in the absence of known coding mutations. CONCLUSION: Previously asymptomatic ornithine transcarbamylase deficiency should be suspected in adult patients who develop recurrent hyperammonemia and encephalopathy following bariatric surgery.

Extensive acrochordons and pancreatic islet-cell tumors in tuberous sclerosis associated with TSC2 mutations.

Acrochordons are frequently encountered benign skin lesions that may occasionally represent underlying pathology. Pancreatic islet-cell tumors are rare neoplasms and few cases have been described in patients with tuberous sclerosis complex (TSC). A 39-year-old man presenting in acute renal failure was referred to us for further diagnostic evaluation of coincidentally noted dysmorphic features. Physical examination revealed over 1,000 acrochordons in addition to findings meeting criteria for TSC. The diagnosis was confirmed by disclosure of mutation in the TSC2 gene. Further evaluation revealed pancreatic islet cell tumors. Acrochordons are a common skin lesion, but when presenting in an atypical manner or unusual number may be a sign of TSC and underlying occult pathology thereby warranting evaluation of TSC2. Additionally, mutations in TSC2 gene may be a risk factor for developing pancreatic islet-cell tumors.