A novel intronic homozygous mutation in the AMT gene of a patient with nonketotic hyperglycinemia and hyperammonemia.

Nonketotic Hyperglycinemia is an autosomal recessive disorder characterized by defects in the mitochondrial glycine cleavage system. Most patients present soon after birth with seizures and hypotonia, and infants that survive the newborn period often have profound intellectual disability and intractable seizures. Here we present a case report of a 4-year-old girl with NKH as well as hyperammonemia, an uncommon finding in NKH. Genetic analysis found a previously unreported homozygous mutation (c.878-1 G > A) in the AMT gene. Maximum Entropy Principle modeling predicted that this mutation most likely breaks the splice site at the border of intron 7 and exon 8 of the AMT gene. Treatment with L-Arginine significantly reduced both the proband's glycine and ammonia levels, in turn aiding in control of seizures and mental status. This is the first time the use of L-Arginine is reported to successfully treat elevated glycine levels.