Molecular genetic characterization of cblC defects in 126 pedigrees and prenatal genetic diagnosis of pedigrees with combined methylmalonic aciduria and homocystinuria

Abstract

BackgroundWe sought to analyse MMACHC variants among 126 pedigrees with cobalamin (cbl) C deficiency and combined methylmalonic aciduria and homocystinuria by Sanger sequencing, characterize the spectrum of MMACHC gene variants, and perform prenatal genetic diagnosis by chorionic villus sampling among these pedigrees.MethodsPeripheral blood was collected from 126 probands and their parents who visited the Genetic Counseling Clinic at our hospital between January 2014 and December 2017, and DNA was extracted from the blood. Then, we amplified the coding sequence and splicing regions of the MMACHC gene by PCR, and the PCR products were further sequenced to detect the variants in each pedigree. In 62 families, pregnant women were subjected to chorionic villus sampling for prenatal genetic diagnosis.ResultsIn total, 31 distinct variants were detected in the 126 pedigrees, and the most frequent variants were c.609G > A (p.Trp203Ter), c.658_660delAAG (p.Lys220del), c.567dupT (p.Ile190Tyrfs*13) and c.80A > G (p.Gln27Arg). Two of these variants have not been previously reported in the literature. One variant [c.463_465delGGG (p.Gly155del)] is a small-scale deletion, and the other variant [c.637G>T(p.Glu213Ter)] is a nonsense mutation. Among the 62 pedigrees who received a prenatal diagnosis, 16 foetuses were normal, 34 foetuses were carriers of heterozygous variants, and the remaining 12 foetuses harboured compound heterozygous variants or homozygous variants. Couples whose foetuses were normal or carriers continued the pregnancy, whereas couples whose foetuses harboured compound heterozygous variants or homozygous variants decided to terminate the pregnancy. The follow-up results were consistent with the prenatal diagnosis.ConclusionsTwo novel MMACHC variants were identified, and prenatal genetic diagnosis is an accurate and convenient method that helps avoid the delivery of combined methylmalonic aciduria and homocystinuria patients.Electronic supplementary materialThe online version of this article (10.1186/s12881-018-0666-x) contains supplementary material, which is available to authorized users.

Proteinuria as a presenting sign of combined methylmalonic acidemia and homocysteinemia: case report

“…MMACHC has a length of 10,736 bp and contains four coding exons and one noncoding exon, and encodes a polypeptide of 282 amino acids [ 9 ]. In China, most variants are clustered in exons 3 and 4, and c.609G > A (p.W203X) is the most frequent cblC mutation [ 9 , 14 ]. Case 1 presented with proteinuria, hematuria, megaloblastic anemia, frequent convulsions and persistent hypertension.…”

Rapid screening of MMACHC gene mutations by high‐resolution melting curve analysis

“…The coding sequence is located in exon 1–4 with a total length of 849 bp, encoding a protein containing 282 amino acids (Lerner‐Ellis et al, 2006). At present, 100 pathogenic MMACHC variants are known (Fischer et al, 2014; Hu, Mei, Liu, & Kong, 2018; Lerner‐Ellis et al, 2009; Liu et al, 2010). However, the mutants of MMACHC greatly vary in incidence.…”

“…However, the mutants of MMACHC greatly vary in incidence. The common mutations of MMACHC in Chinese patients with cblC are c.609G > A (p.Trp203Ter), c.658_660delAAG (p.Lys220del), c.482G > A (p.Arg161Gln), c.80A > G (p.Gln27Arg), and c.609G > A (p.Trp203Ter) mutation alone accounts for almost half of all the mutations (Hu et al, 2018; Liu et al, 2010). The sum of the four most common mutations, c.609G > A (p.Trp203Ter), c.658_660delAAG (p.Lys220del), c.482G > A (p.Arg161Gln), and c.80A > G (p.Gln27Arg), accounts for 72.52% of all pathogenic variants of MMACHC (Our unpublished data).…”

Noninvasive prenatal diagnosis of cobalamin C (cblC) deficiency through target region sequencing of cell‐free DNA in maternal plasma

“… In a clinical setting, sequence analysis of the MMACHC gene and metabolite measurement in chorionic villus cells or cultured amniocytes are used for the prenatal diagnosis of cblC deficiency . However, the invasive nature of these procedures may impose a small but significant risk for miscarriage or infection . …”

“…4 Prenatal diagnosis can provide reproductive choice for at-risk couples and allow initiation of treatment of an affected fetus immediately after birth .4 In a clinical setting, sequence analysis of the MMACHC gene and metabolite measurement in chorionic villus cells or cultured amniocytes are used for the prenatal diagnosis of cblC deficiency . 5 However, the invasive nature of these procedures may impose a small but significant risk for miscarriage or infection .6 The discovery of circulating cell-free fetal DNA (cff-DNA) in maternal plasma allows noninvasive prenatal testing (NIPT), which carries no risk to the fetus or mother . 7 The NIPT of fetal aneuploidies is widely adopted as a prenatal screening method in clinical practice .8 More recently, NIPT has also been available for certain genomic microdeletions and microduplications .9 Noninvasive prenatal diagnosis (NIPD) has extended the potential applications to dominant monogenic disorders, which is confined to the detection of de novo and paternal pathogenic variants .…”