Biochemical and molecular characterization of GALT gene from Indian galactosemia patients: identification of 10 novel mutations and their structural and functional implications

Classical Galactosemia is an autosomal recessive disorder of galactose metabolism caused by severe reduction or absence of the galactose-1-phosphate uridyl transferase (GALT) enzyme. Till date, no reports are available on clinical and molecular spectrum of galactosemia from Indian population. The characterization of underlying GALT gene lesions was performed in 55 unrelated galactosemia patients. The GALT mutational spectrum comprised 16 distinct mutations including 10 previously unreported mutations. N314D was the most common mutation with a frequency of 40% followed by Q188R at 2.7%. The novel GALT gene mutations included 6 missense mutations viz. Y89H, Q103R, P166A, S181F, K285R, R333L; one nonsense mutation, S307X and 3 silent mutations--Q103Q, K210K and H319H. The functional significance of the novel GALT missense mutations was investigated using SNPs&GO and SIFT tools. Further, modeling studies using 3D models of mutant and wild type GALT proteins revealed mutations to exert their effects at the molecular level by altering H-bonds, salt bridges, secondary structure or surface features. The study highlighted the heterogeneity of classical galactosemia in the Indian population and also emphasizes the importance of GALT gene analysis in diagnosis of galactosemia. It also revealed that the Indian GALT mutational profile differs significantly from other populations studied.