[Genotype-phenotype analysis of a homozygous familial hypercholesterolemia pedigree].

Objective: To analyze the genetic characteristics of a five generations pedigree with homozygous familial hypercholesterolemia (HoFH). Methods: Prospective study. Twenty family members included a proband diagnosed as familial hyperlipidemia at the cardiology Department of Xi'an Children's Hospital in October 2018 were research object. Clinical data were collected. Genome DNAs were extracted. Whole exons sequencing was performed on the proband using target capture next generation sequencing. Candidate gene mutation sites identified by bioinformatics were verified by Sanger sequencing in the family members. The genotype-phenotype correlation of the pedigree was analyzed between heterozygous mutation carriers and non-carriers. Results: The proband was a 7-years and 10-month-old boy. He was born with a roundgreen bean size yellow skin protuberance in the skin of the coccyx. Since the age of 3-4 years old, xanthoma-like lesions with a diameter of 0.5-1.5 cm gradually appeared in the skin of bilateral elbow joints, knee joints and Achilles tendon. The height, weight and intellectual development of the child were the same as those of normal children at the same age. No similar xanthoma-like lesion was found in the other family members. The proband's total cholesterol (TC) reached 18.16-21.24 mmol/L, and his low density lipoproteincholesterol (LDL-C) was 14.08-15.51 mmol/L. Carotid ultrasonography showed diffuse sclerotic plaques in bilateral carotid and vertebral arteries, and color Doppler echocardiography revealed aortic valve thickening and calcification. Gene testing identified that the proband carried a homozygous mutation C. 418G>A (p. E140K) in LDLR gene inherited from his parents who had a consanguineous marriage and carried a heterozygous mutation of LDLR-E140K, respectively.The TC, LDL-C and apolipoproteinB (ApoB) of LDLR-E140K gene heterozygous carriers ((8.40±0.13), (6.79±0.01) and (1.95±0.05) mmol/L, respectively) were significantly higher than those of non-carriers ((4.59±0.28), (3.35±0.39) and (0.86±0.10) mmol/L, t=7.269, 4.595, 6.311, respectively, P<0.05). Conclusions: LDLR-E140K gene homozygous mutation is first reported to be associated with most severe phenotype HoFH. The genotype-phenotype analysis of the pedigree shows that the clinical phenotype of the proband with homozygous mutation is the most serious, and all the heterozygous mutation carriers present with hypercholesterolemia phenotype. The investigation confirms that LDLR-E140K is the pathogenic variation of familial hyperlipidemia.目的： 对1个纯合型家族性高胆固醇血症（HoFH）家系进行遗传学分析。 方法： 前瞻性研究。选择西安市儿童医院心内科2018年10月确诊的1个HoFH家系先证者及家系成员共20人为研究对象，收集临床资料，提取基因组DNA，对先证者进行全外显子靶向捕获二代测序，并在家系内进行Sanger测序验证。对家系成员杂合突变携带者和未携带者的基因型与表型进行分析。 结果： 先证者为7岁10月龄男性患儿，生后尾骨处皮肤可见圆形绿豆大小黄色皮肤突起，3~4岁起双侧肘关节、膝关节及跟腱处皮肤逐渐出现直径0.5~1.5 cm的黄色瘤样结节，患儿身高、体重、智力发育与同龄儿相同。家族其他成员无类似皮肤黄瘤。患儿总胆固醇（TC）18.16~21.24 mmol/L，低密度脂蛋白胆固醇（LDL-C）14.08~15.51 mmol/L，颈部超声提示双侧颈动脉及椎动脉弥漫性硬化斑块，心脏彩超提示主动脉瓣增厚、钙化。基因检测确定了先证者LDLR基因携带c.418G>A（p.E140K）纯合突变，分别遗传自患儿父母，二人为近亲结婚，均携带LDLR-E140K基因杂合突变。家系中携带LDLR-E140K基因杂合突变成员TC、LDL-C和载脂蛋白B分别为（8.40±0.13）、（6.79±0.01）、（1.95±0.05）mmol/L，明显高于未携带者[（4.59±0.28）、（3.35±0.39）、（0.86±0.10）mmol/L，t=7.269、4.595、6.311，P均<0.05]。 结论： LDLR-E140K基因纯合突变致儿童HoFH，携带纯合突变的先证者临床表型最严重，携带杂合突变的家系成员均有高胆固醇血症表型，LDLR-E140K是家族性高胆固醇血症的致病性变异。.