Bai Zhouxian, Kong Xiangdong
Genetic and Prenatal Diagnosis Center, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China.
Mol Genet Genomic Med. 2018 Nov;6(6):1053-1067. doi: 10.1002/mgg3.481. Epub 2018 Oct 17.
Congenital aniridia is a severe autosomal dominant binocular developmental disorder, the primary feature of which is congenital absence or hypoplasia of the iris. PAX6 is the main disease-causing gene of congenital aniridia; inheritance is autosomal dominant. But the current mutations do not fully explain this disorder.
We investigated the mutation profile of genes related in three Chinese families with congenital aniridia through targeted sequencing technology. And we validated the candidate variants by PCR-based Sanger sequencing. Different degree impairments of islet function were observed in the patients with aniridia by carbohydrate tolerance butter and insulin release tests in our study.
We identified four novel mutations of PAX6 from three Chinese families with congenital aniridia, which included heterozygous double mutation c.879_880delCA (p.S294Cfs46) and c.1124C>G (p.P375R) in Family 1 with three patients, heterozygous frameshift mutation c.308delG (p.P103Qfs21) in Family 2 with one patient, and c.1192delT (p.S398Pfs*126) in Family 3 with two patients. The three frameshift mutations of PAX6 are co-segregated with the aniridia from controls in the families, but the novel missense mutation is not co-segregated with the phenotype. The frameshift mutations in Family 1 and Family 2 have effects to truncate the protein, but the frameshift mutation in Family 3 will prolong it. We confirmed the phenomenon of male gonadal mosaicism of PAX6 by the sequencing of two linked novel mutations in Family 1. Most of the patients with isolated aniridia have different degrees of islet damage through related clinical tests.
It is therefore noteworthy that we found different types of pathogenic mutation, which have effects of truncating or prolonging protein leaded by frameshift mutation. Our results of this study extended the pathogenic mutation spectrum of PAX6 for congenital aniridia and demonstrated the male germline chimerism by molecular experiments.
先天性无虹膜是一种严重的常染色体显性双眼发育障碍，其主要特征是先天性虹膜缺失或发育不全。PAX6是先天性无虹膜的主要致病基因；遗传方式为常染色体显性遗传。但目前的突变并不能完全解释这种疾病。
我们通过靶向测序技术研究了三个先天性无虹膜中国家系中相关基因的突变情况。并通过基于PCR的桑格测序验证了候选变异。在我们的研究中，通过糖耐量试验和胰岛素释放试验观察到无虹膜患者胰岛功能存在不同程度的损害。
我们在三个先天性无虹膜中国家系中鉴定出四个PAX6新突变，其中包括家系1中三名患者的杂合双突变c.879_880delCA（p.S294Cfs46）和c.1124C>G（p.P375R），家系2中一名患者的杂合移码突变c.308delG（p.P103Qfs21），以及家系3中两名患者的c.1192delT（p.S398Pfs*126）。PAX6的三个移码突变在家系中与无虹膜与对照共分离，但新的错义突变与表型不共分离。家系1和家系2中的移码突变会导致蛋白质截断，但家系3中的移码突变会使其延长。我们通过对家系1中两个连锁新突变进行测序证实了PAX6的男性性腺嵌合现象。大多数孤立性无虹膜患者通过相关临床检查存在不同程度的胰岛损害。
因此，值得注意的是我们发现了不同类型的致病突变，这些突变由移码突变导致蛋白质截断或延长。我们这项研究结果扩展了先天性无虹膜PAX6的致病突变谱，并通过分子实验证明了男性生殖系嵌合现象。
