低磷酸酶血症一家系组织非特异性碱性磷酸酶TNSALP基因突变分析

 目的 对1例儿童型低磷酸酶血症（HPP）患者及家系进行临床分析及基因突变检测，以探讨HPP的致病机制。方法 针对1例罕见的HPP患者的典型临床特点，进行实验室检验及影像学检查。进而收集患者及其亲属外周血，提取基因组DNA。针对ALPL基因12个外显子及附近内含子区合成引物，经PCR扩增后，直接对产物测序检测突变。结果 显示患者血碱性磷酸酶水平显著降低，骨骼具有佝偻病样改变；患者ALPL基因存在c.18delA及c.G407C两种突变。前者所致移码突变使得翻译提前终止，形成的截短蛋白 (p.V7Yfs18X)丧失了发挥酶活性及骨骼矿化作用的重要区域；而c.G407C导致其编码的氨基酸由精氨酸变为脯氨酸（R136P）。进一步检索PubMed及ALPL基因突变数据库，以上突变在国内外均未见报道。临床表现正常的患者母亲及祖母、父亲分别携带c.18delA和c.G407C突变，该家系符合常染色体隐性遗传。结论 ALPL基因c.18delA和c.G407C两种新突变，与HPP临床表现密切相关。

Detection of two novel mutations in the tissue-nonspecific alkaline phosphatase (TNSALP)gene in a patient with hypophosphatasia

Objective In this study，the clinical and genetic characteristics of a Chinese boy with childhood hypophosphatasia was analyzed, and genetic mechanism and genotype-phenotype correlation discussed. Methods According to the clinical manifestation and laboratory findings, the preliminary diagnose of hypophosphatasia was given to the patient. Furthermore, genomic DNA was extracted from peripheral blood leukocytes of the patient, his family members and 50 ethnically matched, unrelated controls. All the 12 exons and ?anking intron sequences of the ALPL gene were ampli?ed by PCR. Direct DNA sequence analysis was performed by automated DNA sequencing. Results Sequence analysis of PCR products in the proband indicated that HPP originated from the heterozygous mutations c.18delA and c.G407C of the ALPL gene. The c.18delA mutation results in frameshift and premature termination of the translation. The predicted truncated protein (p.V7YfsX18) lacks almost all the crucial regions for the enzyme function and bone mineralization. The nucleotide transition G>C at position 407 resulted in an amino acid exchange from arginine 136 to praline. Both of the two mutations were not detected in 50 normal controls and not reported previously. After searching PubMed and the TNSALP gene mutations database, both of the two mutations were not reported previously. Pedigree analysis showed that the c.18delA and c.G407C had been inherited from the proband’s mother and father, respectively. In addition, his grandmother was also found carring the mutation c.G407C. According to the family pedigree, the disease was transmitted as an autosomal recessive trait. Conclusion The two novel mutations c.18delA and c.G407C in ALPL gene may provide new insights into the pathological mechanism and clinical manifestation of this rare disease.