Objective To investigate the clinical and molecular genetic features of a family with late-onset methylmalonic aciduria and homocystinemia,and to review related articles.Methods Sanger sequencing was performed for one family with mental symptoms as initial symptoms to detect MMACHC gene mutations,and related articles were summarized and analyzed.Results A novel missense mutation,c.160A>C,in exon 2,and a previously reported missense mutation,c.482G>A,in exon 4 of MMACHC gene were detected in the proband.Literature review found that cognitive impairment and mental and behavioral disorders were the most common symptoms in patients with this disease,and the most common mutations of MMACHC gene were c.609G>A and c.271dupA.Conclusions The compound heterozygote mutations of c.160A>C and c.482G>A in MMACHC gene are the cause of late-onset methylmalonic aciduria with homocystinemia in this patient,suggesting that MMACHC gene may have a pathogenic effect in this disease.This disease is rare and has high clinical heterogeneity,which may lead to missed diagnosis and misdiagnosis.This disease should be considered in case of unexplained mental and behavioral disorders.