Primary Hyperoxaluria Type 1 with Homozygosity for a Double-mutated Allele in a 2-year-old Child.

Primary hyperoxaluria (PH) Type 1 is a rare, genetic disorder caused by deficiency of the liver enzyme alanine-glyoxylate aminotransferase, which is encoded by gene. We report a 2-year-old South Indian Tamil child with nephrocalcinosis due to PH Type 1, in whom a homozygous genotype for two missense mutations in the gene was found: first, a C to G transversion (c. 32C>G) in exon 1 resulting in the amino acid substitution p.Pro11Arg; second, a T to A transversion (c. 167T>A) in exon 2 resulting in p.Ile56Asn. A therapy based on potassium citrate and pyridoxine was started. This is the first report of molecular testing-proven childhood onset-PH Type 1 from South India and is notable for the co-occurrence of two missense mutations in one allele, which might lead to different and more severe phenotype than each mutation alone. To the best of our knowledge, allele carrying two already known mutations has not been previously reported.