Application of gene capture technology combined with next generation sequencing technology on methylmalo-nic acidemia

Abstract

Objective To assess the efficiency and reliability of clinical genetic diagnosis of methylmalonic acidemia(MMA) using new generation sequencing platform(HiSeq2000). Methods 1.Nine patients diagnosed with clinical signs of MMA were recruited.DNA library from the patients were mixed with designed gene capture probe.The whole exons region of 48 genes related to organic acid metabolism were screened using the gene capture combined with high-throughput sequencing.2.The joints were removed and the low quality data were filtered, the data were analyzed by means of SNP and InDel.To avoid the false positive, the abnormal sites were verified using the Sanger sequencing method.3.The detection of the organic acid in the urine was performed through gas chromatography-mass spectrometry and other auxiliary examinations. Results 1.Gene mutation: 7 gene mutations of MMACHC were identified in 7 patients.Seven mutations: c.482G>A, c.567_568insT, c.609G>A, c.440_441del, c.80A>G, c.315C>G, c.90G>A were screened.The mutation c. 440_441del had not been reported before, and others were all related to the disease.Two gene mutations of mutase apoenzyme(MUT) were identified in 1 case, all of which were introns: .c.754-1G>C, c.1677-1G>A.The novel mutation was c. 754-1G>C.No gene mutation was identified in 1 patient.2.Clinical manifestation: all of the patients were development delay, but the degrees were different; 3 patients with convulsion; 1 patient with headache and central facial paralysis; 1 patient with repeated intractable metabolic acidosis; 1 patient with repeated hemolysis.Electroencephalogram of the all patients were abnormal; the result of cranial MRI of the 8 patients were abnormal; In all patients, urine level of methylmalonic acid significantly increased(273.4-146 022.8 times). Blood homocysteine of 8 patients were significantly increased(27.13-396.84 μmol/L, normal<20 μmol/L).3.Sanger sequencing: there were no false positive exists. Conclusions 1.There were not a correlation between the clinical manifestation and gene mutation of the patients with MMA.The c. 609G>A was the hotspot mutation of MMACHC gene in Chinese patients with MMA and homocysteinemia.2.The mutations c. 440_441del and c. 754-1G>C were presumed to be novel mutations.3.Gene capture technology combined with next-generation sequencing technology could be used to interrogate the wealth of data available in the human genome and lay the foundations for counseling of gene.This platform can be readily and timely adopted by clinical molecular diagnosis of MMA and represents a high throughput, high sensitivity, high efficiency and other characteristics approach for screening common genetic diseases. Key words: Gene capture technology; Next-generation sequencing technology; Methylmalonic acidemia; Homocysteinemia; Development delay; Gene mutation