Deng L, Yang M, Fründ S, Wessel T, De Abreu R A, Tischfield J A, Sahota A
Department of Genetics, Rutgers University, Piscataway, New Jersey 08854-8082, USA.
Mol Genet Metab. 2001 Mar;72(3):260-4. doi: 10.1006/mgme.2000.3142.
We have examined the mutational basis of adenine phosphoribosyltransferase (APRT, EC 2.4.2.7) deficiency (MIM 102600) in a patient of Polish origin who has been passing 2,8-dihydroxyadenine (DHA) stones since birth, but has considerable residual enzyme activity in lymphocyte extracts. The five exons and flanking regions of APRT were amplified by PCR and then sequenced. A single T insertion was identified at the intron 4 splice donor site (TGgtaa to TGgttaa:IVS4+2insT) in one allele from the proband, his mother, and brother. A G-to-T transversion in exon 5 (GTC-to-TTC:c.448G>T, V150F) was identified in the other allele, and this mutation was also present in one allele from the father and the paternal grandmother. Tru91 and AvaII digestions of PCR products spanning exons 4 and 5, respectively, confirmed the mutations. The mother was heterozygous for an intragenic TaqI site, but all other family members were homozygous for the presence of this site. IVS4+2insT, located on the allele containing the TaqI site, has been identified previously in several families from Europe, suggesting a founder effect, but the substitution in exon 5 is a novel mutation. IVS4+2insT is known to result in complete loss of enzyme activity, and our results suggest that V150F produces an enzyme that is nonfunctional in vivo but has considerable residual activity in vitro.
我们研究了一位祖籍波兰患者腺嘌呤磷酸核糖转移酶（APRT，EC 2.4.2.7）缺乏症（MIM 102600）的突变基础。该患者自出生以来一直排出2,8 - 二羟基腺嘌呤（DHA）结石，但淋巴细胞提取物中仍有相当程度的残余酶活性。通过聚合酶链反应（PCR）扩增APRT的5个外显子及其侧翼区域，然后进行测序。在来自先证者、其母亲和兄弟的一个等位基因中，在内含子4剪接供体位点发现了单个T插入（TGgtaa变为TGgttaa：IVS4 + 2insT）。在另一个等位基因的外显子5中发现了G到T的颠换（GTC变为TTC：c.448G>T，V150F），并且该突变也存在于来自父亲和祖母的一个等位基因中。分别跨越外显子4和5的PCR产物的Tru91和AvaII消化证实了这些突变。母亲对于基因内的TaqI位点是杂合的，但所有其他家庭成员对于该位点的存在是纯合的。位于含有TaqI位点的等位基因上的IVS4 + 2insT先前已在来自欧洲的几个家族中被鉴定，提示存在奠基者效应，但外显子5中的替换是一个新的突变。已知IVS4 + 2insT会导致酶活性完全丧失，我们的结果表明V150F产生的酶在体内无功能，但在体外有相当程度的残余活性。
