Yue Hua, Zhang Zhen-Lin, He Jin-Wei
Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated the Sixth People's Hospital, Shanghai 200233, 600 Yi-Shan Rd., PR China.
Bone. 2009 Apr;44(4):547-54. doi: 10.1016/j.bone.2008.11.005. Epub 2008 Nov 21.
Progressive pseudorheumatoid dysplasia (PPD) is an autosomal recessive genetic disease and it has been reported that PPD is caused by mutations of the Wnt1-inducible signaling pathway protein 3 (WISP3) gene which is located on chromosome 6q22. Up to date, 16 different mutations in the WISP3 have been identified in patients with PPD in different countries previously, but only two mutations in exon 5 were previously identified from Asian origin. Our study aimed to characterize the clinical manifestations and features of PPD and screen the mutations of the disease causing WISP3, and try to elucidate the molecular pathogenesis of PPD.
Altogether, 153 persons, including 4 affected individuals, 49 unaffected individuals from two unrelated Chinese families, and 100 healthy donors were recruited and genomic DNA was extracted. PPD was diagnosed based on the clinical manifestations, physical examination, characteristics of their bones on X-ray and laboratory results. All 5 exons and their exon-intron boundaries of the WISP3 gene were amplified by polymerase chain reaction (PCR) and sequenced directly.
In family 1, we identified that the proband (IV4) carried a novel non-sense mutation (G46X) which consisted of a homozygous C to T transition at c.8004 in exon 3. This mutation changed codon CAG to TAG and resulted in a subsequent change of the glutamine codon to stop codon and truncation at p. 46. In family 2, a novel missense mutation (C114Y) was found in the three patients (IV6, IV7, IV8), namely, a homozygous G to A transition at c.8209 in exon 3, which resulted in a cysteine (TGT) to tyrosine (TAT) substitution at p.114. Neither G46X nor C114Y was found in 100 normal controls. Meanwhile, we found that these patients had some different phenotypes, compared with the affected individuals with PPD from cases reported previously.
Our study suggests that the novel G46X and C114Y mutations in exon 3 in WISP3 gene are responsible for PPD in Chinese patients. Furthermore, many heterozygous carriers (c.8004C>T and c.8209G>A) are found in the two families, suggesting the existence of a founder effect in the locality where they live, respectively.
进行性假类风湿性发育不良（PPD）是一种常染色体隐性遗传病，据报道，PPD由位于6号染色体6q22上的Wnt1诱导信号通路蛋白3（WISP3）基因突变引起。此前在不同国家的PPD患者中已鉴定出WISP3基因的16种不同突变，但之前仅从亚洲患者中鉴定出5号外显子的两种突变。我们的研究旨在描述PPD的临床表现和特征，筛查导致该疾病的WISP3基因突变，并试图阐明PPD的分子发病机制。
共招募了153人，包括4名患者、来自两个不相关中国家庭的49名未患病个体以及100名健康供体，并提取了基因组DNA。根据临床表现、体格检查、X线骨骼特征和实验室检查结果诊断PPD。通过聚合酶链反应（PCR）扩增WISP3基因的所有5个外显子及其外显子-内含子边界，并直接进行测序。
在家族1中，我们鉴定出先证者（IV4）携带一种新的无义突变（G46X），该突变由3号外显子c.8004处的纯合C到T转换组成。此突变将密码子CAG变为TAG，导致谷氨酰胺密码子随后变为终止密码子，并在第46位截断。在家族2中，在三名患者（IV6、IV7、IV8）中发现了一种新的错义突变（C114Y），即3号外显子c.8209处的纯合G到A转换，导致第114位的半胱氨酸（TGT）被酪氨酸（TAT）取代。在100名正常对照中均未发现G46X和C114Y。同时，我们发现与之前报道病例中的PPD患者相比，这些患者有一些不同的表型。
我们的研究表明，WISP3基因3号外显子中的新突变G46X和C114Y是中国患者PPD的病因。此外，在这两个家族中发现了许多杂合携带者（c.8004C>T和c.8209G>A），分别表明他们居住地区存在奠基者效应。
