Clinical presentation, gene analysis and outcomes in young patients with early-treated combined methylmalonic acidemia and homocysteinemia (cblC type) in Shandong province, China

Abstract

ObjectivesTo estimate the incidence of MMA on newborn screening in Shandong province from May 2011 to May 2014 and summarize the clinical presentation, biochemical features, mutation analysis, and treatment regime of early-treated patients with cblC disease. MethodsBetween May 2011 and May 2014, 35,291 newborns were screened for MMA in Jinan maternal and Child Care Hospital, Shandong province. The levels of C3, C3/C2, methionine and tHcy were measured. Most patients received treatment with intramuscular hydroxocobalamin after diagnosis. Metabolic parameters, clinical presentation and mental development were followed up. ResultsNine patients were identified among 35,291 by newborn screening, giving an estimated incidence of 1:3920 live births for MMA, and all were classified as cblC disease. Among them, five patients received treatment with intramuscular hydroxocobalamin and two patients did not receive any treatment. One patient died of metabolic crises triggered by infection at the age of 38days. Seven different mutations (c.609G>A, c.455_457delCCC, c.394C>T, c.445_446insA, c.658_660delAAG, c.452A>G and IVS1+1G>A) were detected. The mutations (c.455_457delCCC and IVS1+1G>A) are novel. Five patients who received treatment had favorable metabolic response, with both reduction of urine MMA and tHcy and increase of methionine. We obtained 7 records of DQ assessment. The five patients who received treatment presented with developmental delay and obvious neurological manifestations. In two patients who did not receive any treatment, case 8 presented with severe mental retardation and developmental delay, while case 9 had nearly normal DQ values at the age of 11/12years. ConclusionOur study characterized variable phenotypes of neurodevelopment in early-treated cblC patients diagnosed on newborn screening. The long-term outcomes of cblC disease are unsatisfactory in spite of conventional treatment and improvement of biochemical abnormalities. Although the number of patients is too small, the information provided in this work is of value in highlighting possible genotype–phenotype correlation that influences outcomes in cblC disease by future studies.