Late-onset nonketotic hyperglycinemia with a heterozygous novel point mutation of the GLDC gene

Catching the Culprit: How Chorea May Signal an Inborn Error of Metabolism

Background

Movement disorders, particularly chorea, are uncommon in inborn errors of metabolism, but their identification is essential for improved clinical outcomes. In this context, comprehensive descriptions of movement disorders are limited and primarily derived from single cases or small patient series, highlighting the need for increased awareness and additional research in this field.

Methods

A systematic review was conducted using the MEDLINE database and GeneReviews. The search included studies on inborn errors of metabolism associated with chorea, athetosis, or ballismus. The review adhered to PRISMA guidelines.

Results

The systematic review analyzed 76 studies out of 2350 records, encompassing the period from 1964 to 2022. Chorea was observed in 90.1% of the 173 patients, followed by athetosis in 5.7%. Various inborn errors of metabolism showed an association with chorea, with trace elements and metals being the most frequent. Cognitive and developmental abnormalities were common in the cohort. Frequent neurological features included seizures, dysarthria, and optic atrophy, whereas non-neurological features included, among others, facial dysmorphia and failure to thrive. Neuroimaging and biochemical testing played crucial roles in aiding diagnosis, revealing abnormal findings in 34.1% and 47.9% of patients, respectively. However, symptomatic treatment efficacy for movement disorders was limited.

Discussion

This study emphasizes the complexities of chorea in inborn errors of metabolism. A systematic approach with red flags, biochemical testing, and neuroimaging is required for diagnosis. Collaboration between neurologists, geneticists, and metabolic specialists is crucial for improving early detection and individualized treatment. Utilizing genetic testing technologies and potential therapeutic avenues can aid in the improvement of patient outcomes.

Novel homozygous GLDC variant causing late-onset glycine encephalopathy: A case report and updated review of the literature

Glycine encephalopathy (MIM #605899) is an autosomal recessive inborn error of metabolism caused by pathogenic variants in three genes GLDC, AMT, GCSH encoding glycine cleavage enzyme system. We report an 8-year-old boy with late-onset glycine encephalopathy who harbors a novel homozygous GLDC likely pathogenic variant c.707G > A p.(Arg236Gln). Polyhydramnios was noted at fetal ultrasound. He displayed global developmental delay, craniofacial dysmorphism, convulsions. Our report expands the phenotypic and genetic spectrum of late-onset nonketotic hyperglycinemia.

Nonketotic hyperglycinemia: Clinical range and outcome of a rare neurometabolic disease in a single-center

BACKGROUND

Nonketotic hyperglycinemia (NKH) is an autosomal recessive severe life-threatening catostrophic metabolic disorder.

MATERIALS AND METHODS

The present study was conducted in a tertiary reference center in Turkey for six years period. The accurate diagnosis of six NKH patients was based on clinical history of the patients, neurological examinations, seizure semiology, serial electroencephalography (EEG) recordings, neuroimaging findings, metabolic tests and genetic analysis.

RESULTS

The common clinical findings were hypotonia with severe head lag, poor feeding, poor sucking, and intractable seizures. The starting age of the symptoms was between birth and 45 days of age (median: 8 days). The starting age of the seizures was between 30 min of age and 45 days of age (median: 18 days). The age of accurate diagnosis was between 1 month of age and 5.5 months of age (mean: 3.75 ± 1.69 months). The cerebrospinal fluid (CSF) to plasma GLY ratio of the patients was between 0.031 and 0.21 (median: 0.16). The EEG patterns of the patients were suppression-burst, hypsarrhythmia, multifocal epileptic activity, and right centro-occipital epileptic activity on admission. The neuroimaging findings were diffuse hypomyelination, corpus callosum (CC) hypoplasia, CC agenesis and brainstem hypoplasia on the magnetic resonance imaging and glycine peak was evidenced on magnetic resonance spectroscopy. Four of the patients were mutation-positive.

CONCLUSIONS

If a child is encephalopathic and/or hypotonic with severe head lag, early evaluation of the EEG records should be made even without a history of clinical seizures. The disease has a heterogenous course and the clinical outcome depends on the mutation type.

[Clinical and genetic analyses of a family with atypical nonketotic hyperglycinemia caused by compound heterozygous mutations in the GLDC gene]

Nonketotic hyperglycinemia (NKH) is an autosomal recessive hereditary disease caused by a defect in the glycine cleavage system and is classified into typical and atypical NKH. Atypical NKH has complex manifestations and is difficult to diagnose in clinical practice. This article reports a family of NKH. The parents had normal phenotypes, and the older brother and the younger sister developed this disease in the neonatal period. The older brother manifested as intractable epilepsy, severe spastic diplegia, intellectual disability, an increased level of glycine in blood and cerebrospinal fluid, an increased glycine/creatinine ratio in urine, and an increased ratio of glycine concentration in cerebrospinal fluid and blood. The younger sister manifested as delayed language development, ataxia, chorea, mental and behavior disorders induced by pyrexia, hypotonia, an increased level of glycine in cerebrospinal fluid, and an increased ratio of glycine concentration in cerebrospinal fluid and blood. High-throughput sequencing found a maternal missense mutation, c.3006C>G (p.C1002W), and a paternal nonsense mutation, c.1256C>G (p.S419X), in the GLDC gene in both patients. These two mutations were thought to be pathogenic mutations by a biological software. H293T cells transfected with these two mutants of the GLDC gene had a down-regulated activity of glycine decarboxylase. NKH has various phenotypes, and high-throughput sequencing helps to make a confirmed diagnosis. Atypical NKH is associated with the downregulated activity of glycine decarboxylase caused by gene mutations.

The genetic basis of classic nonketotic hyperglycinemia due to mutations in GLDC and AMT

PURPOSE

The study's purpose was to delineate the genetic mutations that cause classic nonketotic hyperglycinemia (NKH).

METHODS

Genetic results, parental phase, ethnic origin, and gender data were collected from subjects suspected to have classic NKH. Mutations were compared with those in the existing literature and to the population frequency from the Exome Aggregation Consortium (ExAC) database.

RESULTS

In 578 families, genetic analyses identified 410 unique mutations, including 246 novel mutations. 80% of subjects had mutations in GLDC. Missense mutations were noted in 52% of all GLDC alleles, most private. Missense mutations were 1.5 times as likely to be pathogenic in the carboxy terminal of GLDC than in the amino-terminal part. Intragenic copy-number variations (CNVs) in GLDC were noted in 140 subjects, with biallelic CNVs present in 39 subjects. The position and frequency of the breakpoint for CNVs correlated with intron size and presence of Alu elements. Missense mutations, most often recurring, were the most common type of disease-causing mutation in AMT. Sequencing and CNV analysis identified biallelic pathogenic mutations in 98% of subjects. Based on genotype, 15% of subjects had an attenuated phenotype. The frequency of NKH is estimated at 1:76,000.

CONCLUSION

The 484 unique mutations now known in classic NKH provide a valuable overview for the development of genotype-based therapies.Genet Med 19 1, 104-111.