Identification of a novel homozygous intron 3 splice site (A>T) mutation in the ARG1 gene in cerebral palsy pediatric cases from Odisha, India.

Background: Arginase enzyme is essential for the catalysis of the last step of the urea cycle, resulting in the conversion of L-arginine to L-ornithine and urea. Arginase deficiency could lead to hyperarginemia, an autosomal recessive disorder of the urea cycle that could result in developmental manifestations after the first year of life, followed by gradually progressive atonic cerebral palsy, spastic quadriplegia, and mental decline. ARG1 mutations have been reported in hyperarginemia patients of Western countries because they exhibited reduced arginase activity. Hence, it is important to assess ARG1 mutations in cerebral palsy cases with hyperarginemia in different populations.

Methods And Results: This study involved two unrelated pediatric patients from two non-consanguineous East Indian families, exhibiting a range of manifestations, including hypotonia of all limbs, mental retardation, and multiple episodes of seizure. The onset of the disease ranged from 1 to 3 years of age. Hyperammonemia (> 250 micromoles) and serum hyperarginemia (> 350 micromoles) were observed in both the patients. Whole-genome sequencing, followed by Sanger sequencing of both the patients confirmed the presence of a homozygous 3' splice site variation in intron 3 of the ARG1 gene (chr6: g.131902357A>T) that affects the invariant AG acceptor splice site of exon 4 (c.330-2A>T; ENST00000356962.2).

Conclusion: The study reported the identification of a novel ARG1 mutation in two different unrelated pediatric cases from Odisha, India associated with hyperarginemia. The pathogenicity of the mutation was robustly supported by the clinical phenotype, complete co-segregation with the disease, and biochemical observations.