BSCL2基因复合杂合突变导致先天性全身性脂肪萎缩的分子机制研究

A study of congenital generalized lipodystrophy(CGL)caused by BSCL2 gene mutation

先天性全身性脂肪萎缩(congenital generalized lipodystrophy,CGL)是一种极端罕见的常染色体隐性遗传病,表现为明显的全身脂肪极度缺失,肌肉感明显,并伴有一系列的代谢指标异常,包括严重的胰岛素抵抗,高血糖,高脂血症,脂肪肝以及黑棘皮等。本文针对1例CGL患者及其家系进行研究。先证者为19岁年轻女性,自幼皮下脂肪缺如,血清瘦素水平仅0.14μg/L。对患者及其亲属(父母、弟弟)进行全基因组检测,显示该患者BSCL2基因5号外显子存在复合杂合突变(c.560A>G和c.565G>T),c.560A>G突变导致对应编码的187位的氨基酸由酪氨酸突变为半胱氨酸(p.Y187C),从而引起BSCL2编码的SEIPIN蛋白发生错义突变;c.565 G>T突变引起对应编码的189位氨基酸转为终止密码子(p.E189X),产生蛋白截短突变。经Sanger测序验证,患者父亲携带c.565G>T杂合突变,患者母亲携带c.560A>G杂合突变,患者弟弟未携带BSCL2基因致病性突变。本研究通过转染突变p.Y187C质粒至HEK293细胞,观察到SEIPIN蛋白量及与甘油-3-磷酸酰基转移酶(glycerol-3-phosphate acyltransferase,GPAT3)互作减少;原代培养的患者皮肤成纤维细胞体外功能实验表明,患者的SEIPIN蛋白量明显低于正常健康人,加入组蛋白去乙酰化酶抑制剂(histone deacetylase inhibitors,HDACis)可部分挽救SEIPIN蛋白表达。此外,油酸刺激下患者皮肤成纤维细胞脂滴小于正常健康人。本文同时综述国内外既往文献中报道的BSCL2基因突变位点,丰富了CGL的临床表型谱和致病基因突变谱,有助于提高临床医生对CGL的临床诊治和致病机制的理解。

Congenital generalized lipodystrophy(CGL)is an extremely rare genetic disease mainly characterized by absence of whole-body adipose tissue and metabolic dysfunctions such as insulin resistance,diabetes mellitus,hypertriglyceridemia,hepatic steatosis,and acanthosis nigricans.In this study,we reported a novel case of a young woman patient with CGL.The patient came to the hospital for early-onset lipodystrophy and diabetes.She was 19-year-old with a height of 160 cm,a weight of 46 kg,BMI of 17.9 kg/m2,and a serum leptin level of 0.14μg/L.Genomic DNA was extracted from blood samples of the patient and her family members,including her mother,father and brother.Genetic analysis revealed compound heterozygous mutations of the BSCL2 gene(c.560A>G and c.565G>T)in the patient.Her father carried a heterozygous mutation(c.565G>T),and her mother carried a heterozygous mutation(c.560A>G)in the BSCL2 gene.The mutant p.Y187C plasmid was transfected into HEK293T cells.The protein expression of SEIPIN and its interaction with glycerol-3-phosphate acyltransferase(GPAT3)were observed to be reduced.In addition,based on primary cultured skin fibroblasts from the patient,SEIPIN protein was decreased,and lipid droplets were much smaller when fatty acid was stimulated compared with those observed from healthy subject controls.However,histone deacetylase inhibitors(HDACis)was found capable of rescuing SEIPIN protein in fibroblasts of the patient.In addition,we further summarized and discussed gene mutations of BSCL2 reported in the current literature.Collectively,these findings have expanded the clinical phenotype and pathogenic gene spectrum of CGL,which might help clinicians to achieve better management of lipodystrophy.