视网膜色素变性患者的相关致病基因PDE6B突变及其临床表型分析

目的：了解磷酸二酯酶β亚单位（phosphodiesterase β subunit,PDE6B）基因突变在我国视网膜色素变性（retinitis pigmentosa,RP）患者中的突变形式及其临床表型特征。方法：应用聚合酶链反应-异源双链-单链构像多态性及DNA序列分析技术,对收集的35个常染色体隐性家系和55例散发RP患者进行PDE6B基因的22个外显子和5′-端非编码区（5′-UTR）全基因扫描,并行眼部检查及家系分析。结果：检测出1例散发性RP患者第6外显子第2492位点T→C碱基突变异致其编码氨基酸由甘氨酸变为丝氨酸,第10外显子5′-端上游（第9内含子内）第27与28碱基之间有2个碱基（TG）插入突变。以上两种突变在100例正常人中均未检测出。RP患者表现为视乳头萎缩、血管变细及色素散布。多焦视网膜电图检测提示视杆细胞受损较重。1例常染色体隐性家系患者PDE6B基因第11外显子5′-端上游第19位碱基（第10内含子内）发生G→A颠换。另2例散发RP患者分别发现第4外显子5′-端上游30与31碱基间2个碱基（GT）插入和第18外显子3′-端下游第15个碱基发生G→C转换。结论：PDE6B基因的复合杂合突变可能是我国散发性RP患者的致病基因,通常以视杆细胞受累较重,其眼部临床表现符合典型的RP患者特征,我国RP患者的PDE6B基因内含子变异呈多种形式。

A study of PDE6B gene mutation and phenotype in Chinese cases with retinitis pigmentosa

OBJECTIVE: To identify the mutation spectrum of phosphodiesterase beta subunit (PDE6B) gene, the incidence in Chinese patients with retinitis pigmentosa (RP) and their clinical phenotypic characteristics. METHODS: Screening of mutations within PDE6B gene was performed using polymerase chain reaction-heteroduplex-single strand conformation polymorphism (PCR-SSCP) and DNA sequence in 35 autosomal recessive (AR) RP and 55 sporadic RP cases. The phenotypes of the patients with the gene mutation were examined and analyzed. RESULTS: Novel complex heterozygous variants of PDE6B gene in a sporadic case, a T to C transversion in codon 323 resulting in the substitution of Gly by Ser and 2 base pairs (bp: G and T) insert between the 27th-28th bp upstream of the 5'-end of exon 10 were both present in a same isolate RP. But they are not found in 100 unrelated healthy individuals. Ocular findings showed diffuse pigmentary retinal degeneration in the midperipheral and peripheral fundi, optic atrophy and vessel attenuation. Multi-focal ERG indicated that the rod function was more severely deteriorated. A mutation was found in a case with RP in a ARRP family, a G to A transversion at 19th base upstream 5'-end of exon 11 (within intron 10) of PDE6B gene. A sporadic RP carried a sequence variant of PDE6B gene, a G to C transition, at the 15th base adjacent to the 3'-end of exon l8. In another isolate case with RP was found 2 bp (GT) insert between 31st and 32nd base upstream 5'-end of exon 4 (in intron 3) of PDE6B gene. CONCLUSIONS: There are novel complex heterozygous mutations of PDE6B gene responsible for a sporadic RP patient in China. This gene mutation associated with rod deterioration and RP. Several DNA variants were found in introns of PDE6B gene in national population.