A novel missense mutation in a neonate with nonketotic hyperglycinemia

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 of Infants in Taiwan

BACKGROUND

Nonketotic hyperglycinemia (NKH) is a rare, inherited disease, with very poor outcome. It is difficult to confirm the diagnosis due to nonspecific presentations and rapid progression. The incidence was reported in a few countries. We report the clinical and genetic features of typical neonatal NKH with novel splicing mutation, c.1058+3A>C, in the intron 7 of the glycine decarboxylase (GLDC) gene. Furthermore, this study aimed to delineate the estimated incidence and clinical characteristics of NKH in the Taiwanese population.

METHODS

Reports of Health Promotion Administration, Ministry of Health and Welfare of Taiwan, during the period from 2000 to 2013; the Human Gene Mutation Database; and literature regarding NKH in Taiwan were reviewed. Demographic information, age of onset, clinical characteristics, genetic analysis, electroencephalography examinations, and outcome of the patients were analyzed.

RESULTS

The estimated incidence of NKH in the Taiwanese population was 7.2 cases per 1,000,000 live births. Among the 12 cases reported in Taiwan, more than 90% were of neonatal type. Fifty-five percent of affected patients died within 5 years, and all survivors had severe neurologic outcomes. Only three infants underwent genetic analysis during the study period. Two neonatal NKH infants had mutation in the GLDC gene, and the other one, who had late-onset NKH, had mutation in the glutaredoxin 5 gene.

CONCLUSION

Compared with other countries, the estimated incidence of NKH was relatively rare in the Taiwanese population. It is important to characterize all index cases at the genetic level. With more awareness of NKH, increased knowledge of gene mutation, and improvement of diagnostic tools, NKH can be diagnosed more accurately.

Two novel missense mutations observed in nonketotic hyperglycinemia

Nonketotic hyperglycinemia, also known as glycine encephalopathy, is an autosomal recessive disorder of an inborn error of the glycine metabolism, caused by deficiency in the mitochondrial glycine cleavage enzyme. The majority of cases are caused by mutations in P-protein, one of the four components of the glycine cleavage enzyme, glycine decarboxylase. We describe a male neonate with hypotonia, hiccups, and persistent apnea, but without seizures. The patient's glycine level in cerebrospinal fluid and plasma was 328.3 nmol/mL (reference value, 2.2-14.2 nmol/mL) and 1439 nmol/mL (reference value, 232-740 nmol/mL), respectively. The cerebrospinal fluid/plasma ratio of 0.228 represented an increase (normal range, <0.04). Two novel heterozygous missense mutations (c.1130C>T (p.A377V) and c.2081_2088del (p.A694DfsX11) in exons 8 and 18) in the glycine decarboxylase gene confirmed the diagnosis of nonketotic hyperglycinemia.

Complex rearrangement involving 9p deletion and duplication in a syndromic patient: genotype/phenotype correlation and review of the literature

We describe a 7-year-old boy with a complex rearrangement involving the whole short arm of chromosome 9 defined by means of molecular cytogenetic techniques. The rearrangement is characterized by a 18.3 Mb terminal deletion associated with the inverted duplication of the adjacent 21,5 Mb region. The patient shows developmental delay, psychomotor retardation, hypotonia. Other typical features of 9p deletion (genital disorders, midface hypoplasia, long philtrum) and of the 9p duplication (brachycephaly, down slanting palpebral fissures and bulbous nasal tip) are present. Interestingly, he does not show trigonocephaly that is the most prominent dysmorphism associated with the deletion of the short arm of chromosome 9. Patient's phenotype and the underlying flanking opposite 9p imbalances are compared with that of reported patients and the proposed critical regions for 9p deletion and 9p duplication syndromes.

Late-onset nonketotic hyperglycinemia caused by a novel homozygous missense mutation in the GLDC gene

Nonketotic hyperglycinemia (NKH) is an inborn error of the glycine metabolism. A 9-year-old boy with learning disability and intermittent choreoathetosis during febrile illnesses had elevated plasma glycine level and CSF/plasma glycine ratio (0.044) and a novel homozygous missense mutation (c.605C>T; p.Ala202Val) in the GLDC gene, confirming the diagnosis of NKH. This is the first report of late-onset NKH with a confirmed underlying genetic defect. NKH should be in the differential diagnosis of intermittent choreoathetosis.