一例罕见的新的TCIRG1基因杂合性突变引起的婴儿恶性石骨症

An unusual and novel heterozygous TCIRG1 mutation causes infantile malignant osteopetrosis

目的:研究1例婴儿恶性石骨症患者的致病基因及其突变。TCIRG1和CLCN7是婴儿恶性石骨症最常见的致病基因。前者被认为是纯合性致病基因,国外只有6例其杂合性改变也致本病的报导,而我国无杂合性突变导致本病的报道。方法:通过骨组织X线检查结合临床症状及体征确诊1例散发性婴儿恶性石骨症患者。提取患者及其父母的外周血基因组DNA,PCR扩增TCIRG1和CLCN7基因外显子及其剪切位点序列,对PCR产物直接测序。用TCRIG1基因附近的微卫星标记和SNP构建患者及其父母的单倍型。用染色体微阵列分析技术对患者及其母亲进行TCIRG1基因拷贝数目变异的检测。结果:患者TCIRG1基因第5号外显子内发现一个4个碱基的缺失突变c.449_452del AGAG(p.Gln149Glnfs16),该突变使得基因3’端编码的666个氨基酸被截断,失去了整个ATP酶V0复合结构域。患儿双亲TCIRG1和CLCN7基因的突变检测及单倍体构建证实该突变来源于患者父亲。染色体微阵列分析未发现患儿及其母亲携带有任何累及TCIRG1及CLCN7基因的拷贝数目变异。结论:本研究发现了1例TCIRG1基因新的杂合性突变所致的婴儿恶性石骨症。这是我国TCIRG1基因杂合性突变引起婴儿恶性石骨症的首例报道。这个发现可用于婴儿恶性石骨症的分子诊断。

AIM： To investigate the underlying genetic changes of a Chinese patient with infantile malignant osteopetrosis（ IMO）. IMO is a monogenic disease,mostly caused by mutations of TCIRG1 and CLCN7 genes. The former is believed a homozygous gene and only cause the disease in homozygous or compound heterozygous status. However,it has been reported that heterozygous mutations also cause the disease in 6 non-Chinese cases. METHODS： Genomic DNA was extracted from peripheral blood of the patient and his parents. All exons and splice sites of TCIRG1 and CLCN7 genes were amplified by PCR followed by Sanger sequencing. Mutation detection in the 2 genes was also investigated in the parents.Haplotypes were constructed by variations obtained in mutation detection and microsatillites flanking TCIRG1 gene in the family by Cyrillic. Chromosomal microarray analysis（ CMA） was performed to detect copy number variations（ CNV） of the patient and his mother. RESULTS： A novel mutation c. 449_452del AGAG（ p. Gln149Glnfs16） was detected in the patient. This mutation truncated 666 amino acids at the C terminal of the V-ATPase 116 k D isoform a3 protein. It wiped out the entire ATPase V0 complex and was predicted to result in total loss of protein function. This mutation was also detected in the patient＇s father. No pathogenic mutation was detected in CLCN7 gene. CMA did not reveal any CNV involving TCIRG1 or CLCN7 gene. CONCLUSION： We reported a novel heterozygous mutation of TCIRG1 gene causing IMO. This represents the first IMO case in China caused by heterozygous TCIRG1 gene mutation.