Characteristics of clinical manifestations and molecular genetics of late-onset cobalamin C deficiency / 中华神经科杂志

ABSTRACT

Objective To investigate the characteristics of clinical manifestations and genetics of late-onset cobalamin (cbl) C deficiency,also named as combined methylmalonic acidemia and homocystinemia, cblC type. Methods We reviewed 26 late-onset cblC deficiency patients diagnosed in Qilu Hospital, Shandong University from 2012 to 2017 and analysed the clinical, biochemistry, neuroimaging, follow-up and MMACHC gene data. Results Among the 26 patients, male:female ratio is 11:15, with the age of diagnosis from 4 to 39 years and sibling comorbidity in 4 families. The clinical manifestaions of nervous system included spastic paraplegia,mental and behavior disorder,intelectual decline,epilepsy,ataxia,dystonia and peripheral neuropathy. There were four cases with proteinuria at onset. At first visit, the levels of serum total homocystinuria of all patients were elevated, from 61.4 to 193.4μmol/Lwith methylmalonic acidemia. The neuroimaging data of the 26 cases showed 11 with cerebral atrophy, 10 with thoracic spinal cord atrophy, five with brain parenchymal lesions, three with longitudinal myelopathy which were reversible in follow-up, one with syringomyelia, one with multiple cerebral artery stenosis. In all the cases, cobalamins were supplied parenterally and folate, betaine, L-carnitine, vitamin B6 were supplied orally during acute metabolic crisis, and the symptoms of acute encephalopathy disappeared but symptoms of spastic paraplegia had little improvement. In chronic stage, frequency of intramuscular injection of hydroxocobalamine could be decreased while the index can still be improved. All the 26 cases had definite mutations in MMACHC gene, the most common mutations of which were found to be c.482G>A(15/52) and c. 609G>A(13/52). Conclusions Homocystine is the important biomarker for cblC deficiency. Once diagnosed, parenteral hydroxocobalamin and oral betaine should be supplied for a lifetime with good prognosis. The most common mutations of MMACHC gene in our cases are c. 482G>A and c. 609G>A missense mutations.