Mutation Analyses in Selected Exons of the MUT Gene in Indian Patients with Methylmalonic Acidemia

Abstract

Deficiency or diminished activity of a cobalamin dependent enzyme methylmalonyl-CoA mutase causes inborn error of metabolism called methylmalonic acidemia (MMA). In this study we elucidated the spectrum of mutations in 21 Indian mut MMA patients by direct sequencing. Sequence analysis identified a total of 70 mutations in exon 2, 9, 11 and 12 of MUT gene. Out of which 26 mutations were predicted to be deleterious and rest were benign. The 23 novel mutations consist of four nonsense mutations (p.N6*, p.G539*, p.E609* and p.I671*), twelve missense mutations (p.K128I, p.N547T, p.D554Y, p.A558T, p.R559P, p.A631T, p.I647T, p.E656D, p.V657E, p.Q660H, p.K679N, and p.G696Y) and seven frame shift mutations (c.375_376insA, c.1642delA, c.1655delC, c.1825_1826insT, c.1957delGA, c.2014delA and c.2062_2063insGA). All of them are point mutations or micro rearrangements. Three of these mutations (p.K621N, p.G648D, p.G630E) have been previously reported; all of them are missense mutations. The mutations are distributed throughout the exon 2, 9, 11 and 12, 38.4 % mutation are located in exon 12.

Keywords: GCMS; LCMSMS; MUT gene; Methylmalonic acidemia; Mutation analysis; Vitamin B12 deficiency.

Fig. 1

Gel picture of amplified exons (2, 9, 11, 12) and ladder of 50 bp showing the band size. M = 50 bp ladder molecular marker, lane 1 exon 2, lane 2 exon 9, lane 3 exon 11 and lane 4 exon 12

Fig. 2

Diagram of exon and intron showing various mutations and partial nucleotide alignment of the exon 12 of MCM for the studied patients, positions of individual mutations are indicated by arrow mark. Row 1 homo sapiens, row 2–13 studied patients and row 14 consensus sequence

Fig. 3

a Overall architecture of the enzyme methylmalonyl-CoA mutase with bound Cobalamin (Vitamin B12) in the catalytic centre and the structural locations of the observed missense mutations. b Native valine-657 substituted with longer and polar glutamate. c Native Arg-559 substituted with smaller and non-polar proline