Yang Junli, Wang Qiong, Zhuo Qingcui, Tian Huiling, Li Wen, Luo Fang, Zhang Jinghui, Bi Dan, Peng Jing, Zhou Dong, Xin Huawei
Department of Pediatrics, Qilu Hospital of Shandong University, Jinan, China.
Institute for Biology and Medicine, Wuhan University of Science and Technology, Wuhan, China.
Mol Genet Genomic Med. 2018 Sep;6(5):739-748. doi: 10.1002/mgg3.428. Epub 2018 Jul 4.
Glycosylphosphatidylinositol (GPI) anchoring is a special type of protein posttranslational modification, by which proteins with diverse function are attached to cell membrane through a covalent linkage between the protein and the glycolipid. Phosphatidylinositol glycan anchor biosynthesis class A (PIGA) is a key enzyme in GPI anchor biosynthesis, somatic mutations or genetic variants of which have been associated with paroxysmal nocturnal hemoglobinuria (PNH), or PIGA deficiency, respectively. More than 10 PIGA pathogenic or likely pathogenic variants have been reported in a wide spectrum of clinical syndromes of PIGA deficiency, including multiple congenital anomalies hypotonia-seizures syndrome 2 (MCAHS2).
Whole-exome sequencing (WES) was performed on two trios, that is., the proband's family and his affected maternal cousin's family, from a nonconsanguineous Chinese family pedigree with hypotonia-encephalopathy-seizures disease history and putative X-linked recessive inheritance. Sanger sequencing for PIGA variant was performed on affected members as well as unaffected members in the family pedigree to verify its familial segregation.
A novel likely pathogenic variant in PIGA was identified through comparative WES analysis of the two affected families. The single-nucleotide substitution (NC_000023.9:g.15343279T>C) is located in intron 3 of the PIGA gene and within the splice acceptor consensus sequence (NM_002641.3:c.849-5A>G). Even though we have not performed RNA studies, in silico tools predict that this intronic variant may alter normal splicing, causing a four base pair insertion which creates a frameshift and a premature stop codon at position 297 (NP_002632.1:p.(Arg283Serfs*15)). Sanger sequencing analysis of the extended family members confirmed the presence of the variant and its X-linked inheritance.
WES data analysis along with familial segregation of a rare intronic variant are suggestive of a diagnosis of X-liked PIGA deficiency with clinical features of MCAHS2.
糖基磷脂酰肌醇（GPI）锚定是一种特殊类型的蛋白质翻译后修饰，通过蛋白质与糖脂之间的共价连接，使具有多种功能的蛋白质附着于细胞膜。磷脂酰肌醇聚糖锚生物合成A类（PIGA）是GPI锚生物合成中的关键酶，其体细胞突变或基因变异分别与阵发性夜间血红蛋白尿（PNH）或PIGA缺乏症相关。在包括多先天性异常-低张力-癫痫综合征2（MCAHS2）在内的多种PIGA缺乏临床综合征中，已报道了10多种PIGA致病或可能致病的变异。
对一个有低张力-脑病-癫痫病史且推测为X连锁隐性遗传的非近亲中国家系的两个三联体进行全外显子测序（WES），即先证者家族及其患病的母亲表妹家族。对家系中的患病成员和未患病成员进行PIGA变异的桑格测序，以验证其家族遗传情况。
通过对两个患病家族的比较WES分析，鉴定出一种新的可能致病的PIGA变异。单核苷酸替换（NC_000023.9:g.15343279T>C）位于PIGA基因的内含子3中，且在剪接受体共有序列（NM_002641.3:c.849-5A>G）内。尽管我们未进行RNA研究，但计算机工具预测该内含子变异可能会改变正常剪接，导致四个碱基对插入，从而产生移码并在第297位产生过早的终止密码子（NP_002632.1:p.(Arg283Serfs*15)）。对扩展家族成员的桑格测序分析证实了该变异的存在及其X连锁遗传。
WES数据分析以及罕见内含子变异的家族遗传情况提示诊断为具有MCAHS2临床特征的X连锁PIGA缺乏症。
