Non-Canonical Splice Site Variant in FREM1 Result in Fetal Renal Agenesis.

Loss-of-function variants in FREM1 have been demonstrated in Manitoba oculotrichoanal syndrome (MOTA) and bifid nose, renal agenesis, and anorectal malformations (BNAR) syndrome, but the broader phenotypic spectrum of FREM1 variants remains incompletely characterized. In this study, we report compound heterozygous variants in a prenatal case of bilateral renal agenesis. Exome sequencing revealed biallelic FREM1 variants: c.5622G>A (p.Trp1874*) and c.3274+4A>G (p.Gly1030_Ile1091del). Minigene and bioinformatic analyses confirmed that the splice site variant induces aberrant splicing and alters transcriptional expression levels. This finding underscores the crucial role of non-canonical splice site variants in FREM1 in the pathogenesis of bilateral renal agenesis.