MMACHC gene mutation analysis in the prenatal diagnosis of methylmalonic aciduria with homocystinuria

Objective To analyse MMACHC mutations for 45 pedigrees with combined methylmalonic aciduria and homocyctinuria by Sanger sequencing, and to discuss the utility of prenatal genetic diagnosis for these pedigrees. Method Peripheral blood was collected from 45 probands and their parents from 2012-2015 in Genetic Counselling Clinic of the First Affiliated Hospital of Zhengzhou University, and the DNA were extracted from the blood. Then the coding sequence of MMACHC gene was amplified by PCR, and the PCR products were further sequenced to detect mutations for each pedigree. For 12 families, chorionic villus sampling was performed on the pregnant women to make prenatal genetic diagnosis. Result There were 14 distinct mutations detected in the 45 pedigrees, and the most frequent mutations are c. 609G>A(W203X), c.658-660delAAG(K220del)and c. 80A>G (Q27A). Two of those mutations have not been reported before: one is a splicing site mutation c. 81+ 1G>A; while the other is a missense mutation c. 665A>G, p.Y222C. Most mutations were found in exon 4.Among the 12 pedigrees who received prenatal diagnosis, 2 fetuses were normal, 7 fetuses were carriers of heterozygous mutation, and the other 3 fetuses were patients with compound heterozygous mutation or homozygous mutation. The couples whose fetuses were normal or carriers continued the gestation, while the couples whose fetuses were patients decided to terminate the pregnancy. After delivery, the outcome of the fetuses was the same as the prenatal diagnose results. Conclusion Two novel mutations of MMACHC were identified and prenatal genetic diagnosis helps to avoid the delivery of combined methylmalonic aciduria and homocyctinuria patients.(Chin J Lab Med, 2016, 39: 613-617) Key words: Amino acid metabolism, inborn errors; Homocystinuria; Carrier proteins; Mutation; Prenatal diagnosis