Mild forms of hypophosphatasia mostly result from dominant negative effect of severe alleles or from compound heterozygosity for severe and moderate alleles

<p>Abstract</p> <p>Background</p> <p>Mild hypophosphatasia (HPP) phenotype may result from <it>ALPL </it>gene mutations exhibiting residual alkaline phosphatase activity or from severe heterozygous mutations exhibiting a dominant negative effect. In order to determine the cause of our failure to detect a second mutation by sequencing in patients with mild HPP and carrying on a single heterozygous mutation, we tested the possible dominant effect of 35 mutations carried by these patients.</p> <p>Methods</p> <p>We tested the mutations by site-directed mutagenesis. We also genotyped 8 exonic and intronic <it>ALPL </it>gene polymorphisms in the patients and in a control group in order to detect the possible existence of a recurrent intronic mild mutation.</p> <p>Results</p> <p>We found that most of the tested mutations exhibit a dominant negative effect that may account for the mild HPP phenotype, and that for at least some of the patients, a second mutation in linkage disequilibrium with a particular haplotype could not be ruled out.</p> <p>Conclusion</p> <p>Mild HPP results in part from compound heterozygosity for severe and moderate mutations, but also in a large part from heterozygous mutations with a dominant negative effect.</p

Rôle de la phosphatase alcaline placentaire dans la grossesse normale et pathologique

La phosphatase alcaline placentaire (PLAP) est une phosphomonoestérase produite spécifiquement par le placenta humain. Son expression augmente avec l avancée de la grossesse pour être maximale au 3ème trimestre. La PLAP est codée par le gène ALPP qui présente une importante variabilité génétique. Différentes études ont mis en évidence une association entre certains variants alléliques ou des variations du taux de PLAP sérique et des pathologies multifactorielles de la grossesse. Dans cette étude, nous nous sommes attachés à préciser le rôle de la PLAP dans la grossesse normale et pathologique et à comprendre les mécanismes moléculaires impliqués. Dans une première partie, nous avons montré l existence d une expression allèle-spécifique du gène ALPP régulée en cis par un polymorphisme du promoteur (rs2014683). Nous avons également mis en évidence une différence d activité enzymatique entre certains variants de la PLAP. D autre part, une étude est actuellement en cours au laboratoire pour tenter de déterminer s il existe une association entre le polymorphisme rs2014683 du gène ALPP, les retards de croissance intra-utérins et/ou le poids des nouveau-nés. Dans une seconde partie, nous avons montré à l aide de puces d expression, que la surexpression du gène ALPP dans les cellules trophoblastiques HTR-8/SVneo induit des modifications significatives des voies de signalisation impliquées dans la croissance cellulaire. D autre part, nous avons montré que la PLAP stimule la prolifération des cellules trophoblastiques. Ces résultats suggèrent que la PLAP pourrait être un régulateur positif de la croissance placentaire.Placental alkaline phosphatase (PLAP) is a phosphomonoesterase produced by the fetal side of human placenta. Its expression increases steadily throughout pregnancy until term. PLAP is encoded by the ALPP gene and displays strong genetic variability. Some variants were reported to be associated with pathologies occuring during pregnancy. In this study, we attempted to precise the role of PLAP in normal and pathological pregnancies. In a first part, we showed that the two most common ALPP allelic variants differ in mRNA expression level. This allele-specific expression is regulated by the sequence variation rs2014683 located in the promoter. A difference of activity was also observed between some PLAP variants. We are currently studying the potential association between the rs2014683 polymorphism in ALPP and intrauterine growth restriction and/or birthweight. In a second part, we used microarray analysis to show that ALPP overexpression induces modifications of cellular growth pathways in trophoblastic HTR-8/SVneo cells.We also showed that PLAP stimulates the proliferation of trophoblastic cells. These results suggest that PLAP could be a positive regulator of placental growth.VERSAILLES-BU Sciences et IUT (786462101) / SudocSudocFranceF

Polymorphisms of Human Placental Alkaline Phosphatase Are Associated with in Vitro Fertilization Success and Recurrent Pregnancy Loss

International audienceFertility is a quantitative, complex character governed by a considerable number of genes. Despite clinical and scientific advances, several cases of human infertility remain unexplained. In the present study, using a positional cloning approach in a mouse model of interspecific recombinant lines, a candidate gene, ALPP, encoding the placental alkaline phosphatase, was identified as being potentially involved in recurrent spontaneous abortion. We then analyzed patients for detecting putative associations between ALPP polymorphisms, in vitro fertilization failures, and miscarriages. ALPP was sequenced in 100 controls and 100 patients affected by recurrent spontaneous abortion, from the same ethnic background. The frequency of several alleles and allelic combinations were different between recurrent spontaneous abortion and control women. One polymorphism induced a coding substitution (Ile89Leu) that was associated with a decreased risk of abortion and in vitro fertilization failure. Thereafter, the population was increased by the analysis of 92 additional controls and 612 additional patients for the coding polymorphism Ile89Leu. We finally show, by functional analysis, that the 89Leu placental alkaline phosphatase has an enhanced alkaline phosphatase activity. This study suggests that ALPP genotyping could be a strong predictor of implantation success

Polymorphisms of human placental alkaline phosphatase are associated with in vitro fertilization success and recurrent pregnancy loss

Fertility is a quantitative, complex character governed by a considerable number of genes. Despite clinical and scientific advances, several cases of human infertility remain unexplained. In the present study, using a positional cloning approach in a mouse model of interspecific recombinant lines, a candidate gene, ALPP, encoding the placental alkaline phosphatase, was identified as being potentially involved in recurrent spontaneous abortion. We then analyzed patients for detecting putative associations between ALPP polymorphisms, in vitro fertilization failures, and miscarriages. ALPP was sequenced in 100 controls and 100 patients affected by recurrent spontaneous abortion, from the same ethnic background. The frequency of several alleles and allelic combinations were different between recurrent spontaneous abortion and control women. One polymorphism induced a coding substitution (Ile89Leu) that was associated with a decreased risk of abortion and in vitro fertilization failure. Thereafter, the population was increased by the analysis of 92 additional controls and 612 additional patients for the coding polymorphism Ile89Leu. We finally show, by functional analysis, that the 89Leu placental alkaline phosphatase has an enhanced alkaline phosphatase activity. This study suggests that ALPP genotyping could be a strong predictor of implantation success. © 2014 American Society for Investigative Pathology

Polymorphisms of human placental alkaline phosphatase are associated with in vitro fertilization success and recurrent pregnancy loss

Fertility is a quantitative, complex character governed by a considerable number of genes. Despite clinical and scientific advances, several cases of human infertility remain unexplained. In the present study, using a positional cloning approach in a mouse model of interspecific recombinant lines, a candidate gene, ALPP, encoding the placental alkaline phosphatase, was identified as being potentially involved in recurrent spontaneous abortion. We then analyzed patients for detecting putative associations between ALPP polymorphisms, in vitro fertilization failures, and miscarriages. ALPP was sequenced in 100 controls and 100 patients affected by recurrent spontaneous abortion, from the same ethnic background. The frequency of several alleles and allelic combinations were different between recurrent spontaneous abortion and control women. One polymorphism induced a coding substitution (Ile89Leu) that was associated with a decreased risk of abortion and in vitro fertilization failure. Thereafter, the population was increased by the analysis of 92 additional controls and 612 additional patients for the coding polymorphism Ile89Leu. We finally show, by functional analysis, that the 89Leu placental alkaline phosphatase has an enhanced alkaline phosphatase activity. This study suggests that ALPP genotyping could be a strong predictor of implantation success. © 2014 American Society for Investigative Pathology