PARS2 and NARS2 mutations in infantile-onset neurodegenerative disorder.

Here we present four unrelated families with six individuals that have infantile-onset developmental delay/regression and epilepsy. Whole-exome sequencing revealed compound heterozygous mutations, c.[283G>A];[607G>A] in a gene encoding prolyl-tRNA synthetase (PARS2) in one family. Two pairs of compound heterozygous mutations, c.[151C>T];[1184T>G] and c.[707T>G];[594+1G>A], and a homozygous mutation, c.[500A>G];[500A>G], in a gene encoding asparaginyl-tRNA synthetase (NARS2) were also identified in the other three families. Mutations in genes encoding aminoacyl-tRNA synthetases cause gene-specific mitochondrial disorders. Biallelic PARS2 or NARS2 mutations are reported to cause Alpers' syndrome, which is an autosomal recessive neurodegenerative disorder characterized by psychomotor regression and epilepsy with variable degree of liver involvement. Moreover, it is known that NARS2 mutations cause various clinical phenotypes, including non-syndromic hearing loss, Leigh syndrome, intellectual disability with epilepsy and severe myopathy. The individuals with PARS2 and NARS2 mutations, we have reported here demonstrate similar neurological features as those previously reported, with diversity in clinical presentation such as hearing loss and seizure type. Our data broaden the clinical and mutational spectrum of PARS2- and NARS2-related disorders.

A novel ZC4H2 gene mutation, K209N, in Japanese siblings with arthrogryposis multiplex congenita and intellectual disability: characterization of the K209N mutation and clinical findings.

OBJECTIVE: To reveal a molecular lesion in the ZC4H2 gene in a Japanese family with arthrogryposis multiplex congenita (AMC) and intellectual disability (ID), and to characterize clinical features of patients with ZC4H2 gene mutations through a literature review. PATIENTS: The probands are male siblings. The elder brother is an 11-year-old boy who showed AMC and ID and frequent postprandial hypoglycemia since 3 years of age. The younger brother also showed AMC, ID, and subclinical postprandial hypoglycemia. The boys' mother also showed a minor malformation of the left toes. METHOD AND RESULT: Using Sanger sequencing, a hemizygous one base substitution designated c.627G > C, which is predicted to substitute asparagine for lysine at amino acid residue 209 (K209N), was identified in the siblings. The mother was heterozygous for this mutation. In silico analysis predicted K209N to be a constituent of a motif required for subcellular localization of the ZC4H2 protein in the nucleus. Transient expression studies of subcellular localization in COS-7 cells showed that compared to the wild-type protein, the transport of the mutant protein into the nucleus was inhibited, thus confirming K209N as a molecular lesion in this family. The literature reviews revealed postprandial hypoglycemia as a new clinical feature that should be considered in ZC4H2 gene-mutation disorders. CONCLUSION: A Japanese family with AMC and ID caused by a novel ZC4H2 gene mutation was reported. Hypoglycemia should be considered one of the features in this disorder.