Exome sequencing identifies the first genetic determinants of sirenomelia in humans.

Sirenomelia is a rare severe malformation sequence of unknown cause characterized by fused legs and severe visceral abnormalities. We present a series of nine families including two rare familial aggregations of sirenomelia investigated by a trio-based exome sequencing strategy. This approach identified CDX2 variants in the two familial aggregations, both fitting an autosomal dominant pattern of inheritance with variable expressivity. CDX2 is a major regulator of caudal development in vertebrate and mouse heterozygotes are a previously described model of sirenomelia. Remarkably, the p.(Arg237His) variant has already been reported in a patient with persistent cloaca. Analysis of the sporadic cases revealed six additional candidate variants including a de novo frameshift variant in the genetically constrained NKD1 gene, encoding a known interactor of CDX2. We provide the first insights for a genetic contribution in human sirenomelia and highlight the role of Cdx and Wnt signaling pathways in the development of this disorder.

[Advantages and limitations of chorionic villous sampling]. / Intérêt et limites de l'examen histopathologique des biopsies de villosités choriales.

Chorionic villous sampling (CVS) has been available for more than twenty years. Together with amniocentesis, it helps the cytogenetician to determine the fetal karyotype for prenatal diagnosis. The choice between these two methods depends on the team and the indication. CVS can now provide sufficient material for both histopathologic and cytogenetic analyses. We evaluated the accuracy of microscopic examination of CVS for detecting primary ovular, uteroplacental vascular (preeclampsia) and inflammatory disorders. Four hundred CVS were examined in the pathology laboratory of Pellegrin Hospital, Bordeaux, France, from January 1995 to February 2008. The results were analyzed according to the indication, the karyotype, the results of placental examination, pregnancy outcome and, when available (following spontaneous or medical termination), fetoplacental findings. The sample was representative of patients requiring CVS for prenatal diagnosis, with respect to maternal age, the stage of pregnancy, and the indications. When used to screen for preeclamsia (prevalence 29.6% in the sample), the sensitivity and specificity of placental biopsy were respectively 56.8% and 87.2% (76.9% in case of intra-uterine growth retardation). When used to screen for chromosomal aberrations (prevalence 7.4%), the specificity was 14.3% and the sensitivity 93.2%. The prevalence of other disorders, and particularly chronic intervillitis, was too low for meaningful analysis. This study shows that histopathologic analysis of chorionic villous samples is useful for detecting the utero-placental vascular origin of intrauterine growth retardation in the absence of other clinical, biological or ultrasound signs, and that it is complementary to cytogenetic analysis. Being a simple and inexpensive examination, histopathologic analysis of CVS could be performed systematically in this indication. Its value and diagnostic signs in other settings need to be determined in larger series.

New insights into genotype-phenotype correlation for GLI3 mutations.

The phenotypic spectrum of GLI3 mutations includes autosomal dominant Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS). PHS was first described as a lethal condition associating hypothalamic hamartoma, postaxial or central polydactyly, anal atresia and bifid epiglottis. Typical GCPS combines polysyndactyly of hands and feet and craniofacial features. Genotype-phenotype correlations have been found both for the location and the nature of GLI3 mutations, highlighting the bifunctional nature of GLI3 during development. Here we report on the molecular and clinical study of 76 cases from 55 families with either a GLI3 mutation (49 GCPS and 21 PHS), or a large deletion encompassing the GLI3 gene (6 GCPS cases). Most of mutations are novel and consistent with the previously reported genotype-phenotype correlation. Our results also show a correlation between the location of the mutation and abnormal corpus callosum observed in some patients with GCPS. Fetal PHS observations emphasize on the possible lethality of GLI3 mutations and extend the phenotypic spectrum of malformations such as agnathia and reductional limbs defects. GLI3 expression studied by in situ hybridization during human development confirms its early expression in target tissues.