Recurrent Increased Nuchal Translucency Led to the Identification of Novel NUP107 Variants.

Abstract

Five percent of fetuses presents increased fetal nuchal translucency. It is a well-known marker for aneuploidy (T21, Turner syndrome) and a variety of monogenic syndromes such as Noonan syndrome and certain skeletal dysplasias, as well as associated with structural malformations such as congenital heart disease. Current diagnostic algorithms for increased nuchal translucency include a rapid test for aneuploidy (fluorescence in situ hybridization, FISH, or quantitative PCR), a cytogenetic analysis (karyotype or chromosomal microarray, CMA) followed by or concurrent with targeted gene panel analysis for RASopathies/Noonan syndrome. Some centers now propose whole exome sequencing as an adjunct, but its usefulness in isolated increased nuchal translucency remains debated. We describe the recurrence of apparently isolated increased nuchal translucency in 2 euploid fetuses. Whole genome sequencing identified two compound heterozygous variants in the NUP107 gene in both fetuses. Biallelic variants in NUP107 are responsible for severe steroid-resistant nephrotic syndrome, either isolated or syndromic (Galloway-Mowat syndrome); in addition to the renal phenotype, the latter also includes intellectual deficiency and dysmorphic features. Pregnancy termination made it impossible to assess whether the NUP107 variants found would have resulted in isolated or syndromic steroid-resistant nephrotic syndrome. However, identifying the responsible gene improved the accuracy of the genetic counseling. This family is an example of the added benefit of introducing WES/WGS in standardized protocols for prenatal diagnosis of euploid fetuses in "isolated" increased nuchal translucency.