MUT genetic analysis in isolated methylmalonic acidemia pedigrees and its application in prenatal diagnosis

Objective To analyze the mutation of MUT with Sanger sequencing technology to explore the feasibility of its application in prenatal diagnosis. Methods MUT sequencing was performed in 24 pedigrees who had history of isolated methylmalonic acidemia (MMA) babies and came to the First Affiliated Hospital of Zhengzhou University and Newborn Screening Center of Maternal and Child Health Hospital of He'nan Province between October 2012 and June 2015 for genetic counseling. Meanwhile, another 100 cases of normal controls also had their MUT gene sequence analyzed. After confirming the genotype of each pedigree, we collected the villi of nine high-risk fetuses in nine pedigrees whose parents were prepared for prenatal diagnosis. Results Totally, 25 kinds of MUT gene mutations were identified among the 24 isolated MMA pedigrees, in which 11 were novel mutations including one nonsense mutation [c.616C>T(p.Q206X)], six missense mutations [c.613G>A(p.E205K), c.894T>G(p.I298N), c.1009T>C(p.F337L), c.1154G>T(p.L385W), c.1663G>A(p.A555T) and c.1675G>A(p.R559G) and four frame shift mutations [c.626-627insC(p.P209Pfs*2), c.755-756insA(p.H252Qfs*6), c.756-757insA(p.M253Nfs*5) and c.1581-1582insA(p.A528Ifs*4)]. None of the above mutations was detected in the controls. Finally, among the nine pedigrees for prenatal diagnosis, two were determined to have normal MUT gene, four were found to be heterozygous mutation carriers of MUT gene and three were confirmed as complex heterozygous or homozygous mutation carriers. Families of fetus who had normal MUT gene or fetuses who were carriers chose to continue the pregnancy, while those who had heterozygous mutation of MUT gene chose termination. The results of follow-up of newborns were consistent with that of prenatal diagnosis. Conclusions We found two novel mutations in MUT gene that might lead to isolated MMA. And Sanger sequencing technology for MUT gene sequencing analysis might effectively avoid the birth of isolated MMA children. Key words: Amino acid metabolism, inborn errors; Methylmalonyl-CoA mutase; Polymerase chain reaction; Prenatal diagnosis