13个白化病家系的遗传学分析及产前基因诊断

Genetic testing and prenatal diagnosis for thirteen Chinese pedigrees affected with oculocutaneous albinism

目的对13个眼皮肤白化病(oculocutaneous albinism,OCA)家系进行致病基因变异鉴定,并以此为基础为患者家庭提供遗传咨询和产前基因诊断。方法收集13例临床确诊的无亲缘关系的白化病患者,并根据患者皮肤和眼睛的临床表现确定疾病分型;采集先证者及其家系成员的外周血样各3〜5 mL;用常规酚-氯仿法提取基因组DNA;对候选基因进行外显子靶向测序(panel sequencing),通过PCR和Sanger测序鉴定致病变异;针对先证者致病基因型对其母所妊娠胎儿进行产前基因诊断。结果在13例OCA先证者中均鉴定出致病变异,其中10例为TYR复合杂合或纯合变异致病,3例为OCA2基因复合杂合变异致病;在鉴定的15个变异中,发现2个新变异(TYR:c.650G>C p.Arg217Pro;OCA2:c.516-2 A>T),并针对错义变异TYR:c.650G>C(p.Arg217Pro)进行致病性分析和蛋白结构预测;对上述家系中的6例高风险胎儿进行产前基因诊断,4例胎儿为致病变异携带者,1例胎儿未携带致病变异,1例胎儿具有与先证者相同的致病基因型。结论在13例OCA先证者中成功完成致病基因型鉴定,发现2种新致病变异,拓展了该病的致病变异谱;为患者家庭提供的遗传咨询和产前基因诊断有效地预防了患儿的出生。

Objective To identify the causative variants in 13 Chinese pedigrees affected with oculocutaneous albinism(OCA)so as to provide genetic counseling and prenatal diagnosis to them.Methods Thirteen unrelated pedigrees with clinically diagnosed OCA were collected and classified based on the manifestation of skin and eyes.With informed consent obtained from the participants,peripheral blood samples were collected from the probands and their family members for the extraction of genomic DNA.Candidate variants were screened by targeted capture and next generation sequencing,and the results were validated by Sanger sequencing.Prenatal diagnosis was provided to the families upon their subsequent pregnancies.Results Causative variants were detected in all probands,including 10 with compound heterozygotes or homozygotes for TYR gene variants and 3 with compound heterozygotes for OCA2 gene variants.Among these,two variants[TYR:c.65OG>C(p.Arg217Pro)and OCA2:c.516-2A>T]were unreported previously.The pathogenicity of the novel TYRt c.65OG>C(p.Arg217Pro)variant was verified through bioinformatic analysis and prediction of three dimensional structure of the protein.Prenatal diagnosis was provided to 6 fetuses with a high risk for OCA.Four fetuses were found to be carriers,one did not carry the variants of the proband,and one was affected with OCA.Conclusion Identification of the pathogenic variants in the 13 probands,including 2 novel ones,has expanded the mutational spectrum of OCA and enabled genetic counseling and prenatal diagnosis for the families.