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OBJECTIVE@#To carry out genetic testing for two families affected with cobalamin C (cblC) and establish a rapid method for the detection of a hotspot pathogenic variant c.609G>A of the MMACHC gene by using a PCR-high-resolution melting curve (PCR-HRM) method.@*METHODS@#Genomic DNA was extracted from peripheral blood samples of the probands and their parents. Potential variants of the MMACHC gene was analyzed by Sanger sequencing. The c.609G>A variant of the MMACHC gene was screened among 100 healthy children with the PCR-HRM method.@*RESULTS@#Sanger sequencing revealed that proband 1 carried compound heterozygous variants c.394C>T and c.609G>A of the MMACHC gene, while proband 2 carried compound heterozygous variants c.482G>A and c.609G>A of the same gene. PCR-HRM analysis of the two probands and the 100 healthy children were consistent with the Sanger sequencing.@*CONCLUSION@#c.609G>A is a hotspot pathogenic variant of the MMACHC gene. The diagnosis of cblC may be rapidly attained through detection by PCR-HRM.
RESUMO
Objective To investigate the spectrum of CYP21A2 gene mutation and the correlation between genotype and phenotype in patients with 21-hydroxylase deficiency in Tianjin and surrounding areas.Methods Genomic DNA was extracted from the peripheral blood samples of the proband.Locus-specific PCR,direct sequencing of PCR amplification products,and multiplex ligation-dependent probe amplification were applied to detect pathogenic gene CYP21A2 and the relationship between genotypes and phenotypes was analyzed.Results (1) Of 35 patients with 21-hydroxylase deficiency,25 were classified as salt-wasting phenotype and 10 were simple virilizing phenotype.(2) 69 mutant alleles were detected in a total of 70 alleles in 35 patients.Only one mutant allele was detected in one patient.Two mutant alleles were detected in all other patients,with the mutation detection rate 98.6％.(3) A total of 6 types of mutations were detected,of which c.293-13C/A＞G (I2G) was the most common,accounting for 57.1％ (40/70),followed by 18.6％ (13/70) for large gene deletion or conversion,and 14.3％ (10/70) for p.I173N.In addition,a novel mutation,c.949C＞T (p.R317X),which has not been reported previously,was detected as a pathogenic mutation.(4) Correlation analysis of genotype and phenotype in 35 children showed that the phenotype predicted by genotype was consistent with the actual salt-wasting phenotype in 31 children,and those in three children were inconsistent with the actual clinical phenotype.Conclusion The mutation characteristics of CYP21A2 gene in patients with 21-hydroxylase deficiency in Tianjin and surrounding areas are slightly different from those reported in other regions in China.A mutation c.949C＞T has not been reported,which enriches the mutation spectrum of CYP21A2 gene and provide the foundation for genetic counseling and prenatal diagnosis.