Hyperammonemia in Russia Due to Carbonic Anhydrase VA Deficiency Caused by Homozygous Mutation p.Lys185Lys (c.555G>A) of the CA5A Gene.

Hyperammonemia due to carbonic anhydrase VA deficiency (OMIM# 615751) is a rare, life-threatening hereditary disease caused by biallelic mutations in the CA5A gene, presenting as encephalopathic hyperammonemia of unexplained origin during the neonatal period and infancy. Here, we present a detailed description of a 5-year-old patient with the homozygous mutation p.Lys185Lys (c.555G>A) in the CA5A gene. This variant was previously described by van Karnebeek et al. in 2014 in a boy of Russian origin. We found a high frequency of carriers of this mutation in Russia; 1:213, which is 7 times higher than the expected frequency calculated based on data on Western European populations. Thus, targeted testing for the mutation p.Lys185Lys (c.555G>A) in the CA5A gene should be useful for early detection by selective screening in neonatal intensive care units.