Clinical analysis and outcome of patients with c. 482G >A variant of MMACHC gene in cblC type methylmalonic acidemia

Abstract

Objective To explore the clinical manifestations, treatment and outcomes of patients with c. 482G>A(p.R161Q)variant of MMACHC gene in cblC type methylmalonic acidemia(MMA). Methods The clinical manifestations, mass spectrometry results, genotypes, treatment and outcomes of 75 patients with cblC type MMA carrying c. 482G>A(p.R161Q)variant were retrospectively analyzed. Results Of the 75 patients, 57(76%)were from newborn screening and one of them had an onset. Among the rest 18 unscreened patients, 2 were diagnosed after their full sisters′ or brothers′ diagnosis, the others were clinical patients. There were 17 clinical patients, with the medium age of onset 12 years old(10 days~26 years old). 12 late onset patients(70.6%)presented with poor academic performance, memory loss, poor expression, and decreased exercise capacity, while 5 early onset patients(29.4%)presented with convulsion and delay of development. All patients were vitamin B12-responsive. The levels of blood propionylcarnitine, the ratio of propionylcarnitine to acetylcarnitine, urinary methylmalonic acid and methyldecanoic acid, and plasma homocysteine were significantly decreased after treatment(P< 0.01). All patients diagnosed from newborn screening had normal development. However, only 3 clinical patients had a rather normal outcomes and the others remained different levels of intelligence and(or)motor dysfunction after treatment. Conclusion The c. 482G>A(p.R161Q)variant of MMACHC gene is associated with late onset cblC type MMA. Patients with this variant have a better response to hydroxycobalamin than other variants. The outcome of patients diagnosed from the newborn screening is good. When symptoms occur, the disability rate is often high. Therefore, newborn screening is a recommended method to prevent this disease. Key words: Methylmalonic acidemia; MMACHC gene; Methylmalonic acid; Propionylcarnitine