Characterizing asparagine synthetase deficiency variants in lymphoblastoid cell lines.

Asparagine synthetase (ASNS) catalyzes the synthesis of asparagine (Asn) from aspartate and glutamine. Biallelic mutations in the ASNS gene result in ASNS Deficiency (ASNSD). Children with ASNSD exhibit congenital microcephaly, epileptic-like seizures, and continued brain atrophy, often leading to premature mortality. This report describes a 4-year-old male with global developmental delay and seizures with two novel mutations in the ASNS gene, c.614A > C (maternal) and c.1192dupT (paternal) encoding p.H205P and p.Y398Lfs*4 variants, respectively. We employed the novel use of immortalized lymphoblastoid cell lines (LCL) to show that the proliferation of the heterozygotic parental LCL was not severely affected by culture in Asn-free medium, but growth of the child's cells was suppressed by about 50%. Asn production by the LCL from both the father and the child was significantly decreased relative to the mother's cells. mRNA and protein analysis of the paternal LCL cells for the Y398Lfs*4 variant revealed reductions in both. Attempts to ectopically express the truncated Y398Lfs*4 variant in either HEK293T or ASNS-null cells resulted in little or no detectable protein. Expression and purification of the H205P variant from HEK293T cells revealed enzymatic activity similar to wild-type ASNS. Stable expression of WT ASNS rescued the growth of ASNS-null JRS cells in Asn-free medium and the H205P variant was only slightly less effective. However, the Y398Lfs*4 variant appeared to be unstable in JRS cells. These results indicate that co-expression of the H205P and Y398Lfs*4 variants leads to a significant reduction in Asn synthesis and cellular growth.

2-Methylglutaconic acid as a biomarker in routine urine organic acids leading to the diagnosis of glutaric acidemia type I in a low excretor.

GA1 (OMIM# 231670) is an organic aciduria caused by defective Glutaryl-CoA dehydrogenase (GCDH), encoded by GCDH. Early detection of GA1 is crucial to prevent patients from developing acute encephalopathic crisis and subsequent neurologic sequelae. Diagnosis of GA1 relies on elevated glutarylcarnitine (C5DC) in plasma acylcarnitine analysis and hyperexcretion of glutaric acid (GA) and 3-hydroxyglutaric acid (3HG) in urine organic acid (UOA) analysis. Low excretors (LE), however, exhibit subtly elevated or even normal plasma C5DC and urinary GA levels, leading to screening and diagnostic challenges. The measurement of 3HG in UOA is thus often used as the 1st tier test for GA1. We described a case of LE detected via newborn screen with normal excretion of GA, absent of 3HG and increased 2-methylglutaconic acid (2MGA), which was detected at 3 mg/g creatinine (reference interval <1 mg/g creatinine) without appreciable ketones. We retrospectively examined UOA of 8 other GA1 patients and the 2MGA level ranged from 2.5 to 27.39 mg/g creatinine, which is significantly higher than normal controls (0.05-1.61 mg/g creatinine). Although the underlying mechanism of 2MGA formation in GA1 is unclear, our study suggests 2MGA is a biomarker for GA1 and should be monitored by routine UOA to evaluate its diagnostic and prognostic value.

Management of COVID-19 infection in organic acidemias.

The COVID-19 pandemic has affected the health and healthcare of individuals of all ages worldwide. There have been multiple reports and reviews documenting a milder effect and decreased morbidity and mortality in the pediatric population, but there have only been a small number of reports discussing the SARS-CoV-2 infection in the setting of an inborn error of metabolism (IEM). Here, we report two patients with underlying metabolic disorders, propionic acidemia and glutaric aciduria type 1, and discuss their clinical presentation, as well as their infectious and metabolic management. Our report demonstrates that individuals with an underlying IEM are at risk of metabolic decompensation in the setting of a COVID-19 infection. The SARS-CoV-2 virus does not appear to cause a more severe metabolic deterioration than is typical.

Biallelic Variants in LAMB1 Causing Hydranencephaly: A Severe Phenotype of a Rare Malformative Encephalopathy.

Case Report A 32-year-old female with a history of three prior pregnancy losses presented for genetic testing following an ultrasonography diagnosis of fetal hydranencephaly. Baby was born via C-section and was noted to have a head circumference of 48 cm, in addition to ocular and cardiac anomalies and dysmorphic features. Whole genome sequencing revealed a homozygous variant in LAMB1 gene. Discussion The pathobiogenesis of hydranencephaly is incompletely understood and is attributed to vascular, infectious, or genetic etiology. Herein we present LAMB1 as a monogenic cause of fetal hydranencephaly which was incompatible with life. Previously, LAMB1 -associated phenotype consisted of cobblestone lissencephaly and hydrocephalus, developmental delay, and seizures. Our proband expands the phenotypic spectrum of this malformative encephalopathy.

Compound heterozygous variants in GOSR2 associated with congenital muscular dystrophy: A case report.

The homozygous missense variant in the GOSR2 gene (c.430G > T) is known to be associated with progressive myoclonic epilepsy (PME). The clinical presentation of GOSR2-related PME involves the development of ataxia, seizures, scoliosis, areflexia, and mildly elevated creatine kinase. Recently, it has been suggested that some compound heterozygous variants in GOSR2 are associated with a predominant muscular dystrophy phenotype. Here we report a case of a now 22 month old female who presented with congenital hypotonia and persistently elevated creatine kinase levels. Whole exome sequencing showed pathogenic compound heterozygous variants in GOSR2 (c.430G > T and c.82C > T). This case contributes to the expanding clinical spectrum of GOSR2 variants with PME representing the milder end and congenital muscular dystrophy representing the more severe end of the spectrum.

Genetic Etiologies of Neonatal Seizures.

Neonates presenting with seizures are frequently assessed and managed by neonatologists in the NICU. Although hypoxic-ischemic encephalopathy and infection are common underlying causes of neonatal seizures, many patients with neonatal epilepsy will have an identifiable genetic etiology. Often these cases will be evaluated in collaboration with a geneticist. The categories of genetic causes of neonatal seizures include 1) structural brain malformations; 2) inborn errors of metabolism; 3) syndromic; and 4) nonsyndromic, single gene. Evaluation of these patients involves a comprehensive history and examination, followed by appropriate investigations and diagnostic genetic testing. Components of the diagnostic process will vary based on the clinical suspicion and differential diagnoses. In certain cases, syndromic surveillance for evaluation of other congenital anomalies may be recommended. Determination of the underlying genetic diagnosis, when present, will have important implications for treatment. Targeted therapies are currently available for specific genetic syndromes, and outcomes may improve with earlier initiation of therapy. Certain genetic diagnoses may also have guideline-based management involving screening for other manifestations of the disorder.

Expanding Phenotypic Spectrum of Cerebral Aspartate-Glutamate Carrier Isoform 1 (AGC1) Deficiency.

CASE: We are reporting the third unrelated case of cerebral aspartate-glutamate carrier isoform 1 (AGC1) deficiency. Patient is a 21-month-old Yemeni male who presented with refractory seizure disorder and developmental arrest. Neuroimaging showed cerebral volume loss and diminished N-acetylaspartate (NAA) peak. Whole exome sequencing revealed a homozygous novel missense variant in the SLC25A12 gene. Patient's seizure frequency abated drastically following initiation of ketogenic diet. DISCUSSION AND CONCLUSION: Cerebral AGC1 deficiency results in dysfunction of mitochondrial malate aspartate shuttle, thereby prohibiting myelin synthesis. There are significant phenotypic commonalities between our patient and previously reported cases including intractable epilepsy, psychomotor delay, cerebral atrophy, and diminished NAA peak. Our report also provides evidence regarding beneficial effect of ketogenic diet in this rare neurometabolic epilepsy.