一个罕见的羧化全酶合成酶缺乏症家系的临床分析与基因诊断

Clinical and gene mutation analysis in a family of holocarboxylase synthetase deficiency

目的对罕见的羧化全酶合成酶缺乏症患儿进行临床诊治和基因突变分析。方法结合临床表现,同时运用血串联质谱、尿气相色谱等,对1例婴儿期起病的疑似羧化全酶合成酶缺乏症/生物素酶缺乏症患儿进行筛查与初步诊断,并提取家系全部成员外周血DNA,应用聚合酶链反应(PCR)扩增生物素酶基因(BTD)的4个外显子和羧化全酶合成酶基因(HLCS)的12个外显子,直接测序,进行先证者及其他家系成员的基因突变检测,以明确患儿基因型与表型之间的关系。结果家系中患儿的发病时间均较早(第一胎男孩为2月+,第二胎女孩为1月),临床主要表现为出生后早期(1-2周)开始头部出现散在湿疹、脓疱疹,3个月时全身发红伴弥漫性浸润性丘疹和脱屑,营养不良貌,毛发稀黄,呼吸急促等。实验室检查发现轻度贫血、代谢性酸中毒,血串联质谱检测发现3-羟基异戊酰基肉碱(C5-OH)水平显著升高,尿有机酸分析显示尿乳酸、丙酮酸、羟基丙酸、丙酰甘氨酸、甲基巴豆酰甘氨酸等显著升高,符合羧化全酶合成酶缺乏症/生物素酶缺乏症的表现。突变检测:家系基因测序BTD基因未发现致病性突变,而在患儿HLCS基因的第9和第10号外显子上发现了致病性的突变位点:c.1522C>T杂合突变和c.1711G>A杂合突变,均为错义突变,50例健康人对照100个等位基因测序未发现这两个位点的突变。因此,患儿诊断明确。经生物素20mg/d补充治疗与营养干预后,患儿全身情况逐渐好转,2周后皮疹愈合,营养状况也逐渐得到改善。结论羧化全酶合成酶缺乏症以神经系统及皮肤损害、代谢性酸中毒为特征。串联质谱和气相色谱分析、基因突变分析有助于鉴别诊断和确诊,口服生物素疗效显著。本研究对一个羧化全酶合成酶缺乏症家系进行了临床分析和基因诊断,明确了患儿发病的遗传学病因,为这个家庭后面的产前诊断,打下了坚实的基础。

Objective：To carry out clinical and genetic diagnosis for a family of the holocarboxylase synthetase deficiency（HLCSD）. Methods：A baby of infantile-onset holocarboxylase synthetase deficiency was preliminarily diagnosed by clinical analysis,tandem mass spectrum（MSMS）and gas chromatography（GCMS）analysis. Further more,DNA extraction from the peripheral blood of the baby and the family,and mutation analysis of the BTD and HLCS gene was carried out,and the relationship between the genotype and phenotype was analysed. Results：Early onset of the phenotypes in two babies was observed. The main clinical manifestations includes eczema,pustular eruption on the head in the early period after birth,and papula,skin desquamation,shortness of breath et al. in the third months after birth. MSMS and GCMS examinations demonstrate elevated level of C5-OH in the blood,and lactic acid,pyruvic acid,alanyl-glycinese in the urine,and these findings were in accordance with the multiple carboxylase deficiency. Mutation studies of the BTD and HLCS gene revealed that two mutations in HLCS gene of this family,which were missense mutation c.1522C〉T and c.1711G〉A,and these mutations were not found in 50 cases of healthy controls. So,the HLCSD were diagnosed definitely. After treatment of biotin（20mg/d）,the nutritional state,dermatological manifestations of the baby were remarkable improved. Conclusion：HLCSD deficiency is characterized by nervous system damage,skin lesions and metabolic acidosis. MSMS,GCMS analysis,and gene mutation analysis may be helpful in the definite diagnosis of this disorder. The effect of early biotin treamtent is satisfactory. In this study,we carried out clinical and genetic diagnosis in a HLCSD pedigree,which lay a solid foundation for prenatal diagnosis of this family.