Small fetuses constitute a large group including healthy small fetuses, fetuses suffering from utero-placental insufficiency or chromosomal abnormality. In the latter case, chromosomal rearrangements may be showed by fetal karyotyping. However, they are usually cryptic and require to be detected by molecular investigations.
In this study, we report on a case of 15q26 microdeletion diagnosed prenatally in a fetus found to have severe intra uterine growth retardation, congenital diaphragmatic hernia and polycystic kidneys identified at 28 weeks of gestation by ultrasonography.
Amniocentesis was performed and revealed a normal karyotype of 46, XX. However, phenotypic features let us to test the 15q26 microdeletion which was confirmed by IGF1R FISH probe.
IGF1R gene is involved in pre and post natal growth. Monozygosity for IGF1R gene is responsible for growth delay, microcephaly, mental retardation, micrognathia and deafness. Congenital diaphragmatic hernia and polycystic kidneys are common findings in 15q26 microdeletion. Genotype phenotype correlation localized critical region implicated in diaphragmatic hernia in 15q26.1–q26.2. NR2F2, CHD2, RGMA and SIAT8B are considered to be most likely candidate genes. Genes involved in kidney defect are little studied. In our case, the deletion must be extended to 15q26.1. Molecular characterization by CGH array is considered to refine genotype phenotype correlation and to localize candidate genes for diaphragmatic hernia and kidney defect.
15q26 microdeletion causes intra uterine and post natal growth retardation variably associated to other malformations. We highlight the importance of molecular analysis in the prenatal diagnosis of cryptic chromosomal abnormalities.