Two novel pathogenic variants of L1CAM gene in two fetuses with isolated X‑linked hydrocephaly: A case report.

Hydrocephalus due to aqueductal stenosis (HSAS; Online Mendelian Inheritance in Man #307000) is a rare X‑linked, recessively‑inherited disease characterized by severe hydrocephaly and occasionally adducted thumbs, in addition to intellectual disability and spasticity in surviving individuals. The present study described two fetuses with severely enlarged ventricles of the brain. The clinical diagnosis of HSAS was made on the basis of family history and sonographic findings. Molecular testing of the L1 cell adhesion molecule (L1CAM) gene revealed two novel hemizygous L1CAM variants, c.998C>T(p.Pro333Leu) and c.2362G>T(p.Val788Phe). The variants affect the highly conserved amino acids which are located in the key domains of the protein (the fourth Ig domain and second FnIII domain, respectively). The two variants were predicted to be 'disease causing' by a number of prediction tools, and have been classified as likely pathogenic following the American College of Medical Genetics and Genomics/Association for Molecular Pathology guidelines. The present study highlights the importance of combining family history, prenatal ultrasonography and molecular testing in the diagnosis of HSAS. The novel variants expand the mutational spectrum of L1CAM gene in the Chinese population, and could be used in genetic counseling, carrier testing of female relatives, and prenatal, as well as preimplantation genetic diagnosis.