A novel splicing variation in L1CAM is responsible for recurrent fetal hydrocephalus

The L1 cell adhesion molecule (L1CAM, OMIM 308840) gene is primarily expressed in the nervous system and encodes the L1 adhesion molecule protein. Variations in L1CAM cause a wide spectrum of X-linked neurological disorders summarized as the L1 syndrome.

We report a 29-year-old pregnant woman who experienced multiple adverse pregnancy outcomes due to recurrent fetal hydrocephalus with an X-linked recessive inheritance. Genomic DNA was extracted from the third aborted male fetus and analyzed via trio whole-exome sequencing (WES). Total RNA was isolated from the pregnant woman to assess splicing variation at the mRNA level, and amniotic fluid was extracted from the woman for prenatal diagnosis on her fourth fetus.

All four male fetuses were affected by severe hydrocephalus. We identified a maternally derived hemizygous splicing variation NM_000425.5:[c.3046 + 1G > A]; NP_000416.1 p.(Gly1016AspfsTer6) (chrX:153130275) in Intron 22 of the L1CAM. This variation disrupts the donor splice site and causes the retention of Intron 22, which results in frame shift and a premature termination codon at position 1021 with the ability to produce a truncated protein without the fifth fibronectin-repeat III, transmembrane, and cytoplasmic domains or to induce the degradation of mRNAs by nonsense-mediated mRNA decay. The same hemizygous variant was also detected in the amniocytes.

This report enhances our knowledge of genetic and phenotypic characteristics of X-linked fetal hydrocephalus, providing a new genetic basis for prenatal diagnosis and pre-implantation prenatal diagnosis.