Unraveling the Role of WDR91: Case Report of a Previously Unrecognized Clinical Entity.

WDR91, a WD40 repeat domain-containing protein, is a key regulator of endosomal trafficking, lysosomal function, and autophagy. It acts as a Rab7 effector, forming a complex with WDR81 to modulate phosphatidylinositol 3-kinase (PI3K) activity, endosomal maturation, and lysosome homeostasis. Loss-of-function variants in WDR91 are considered related to endosomal accumulation, impaired cargo degradation, and neurodegeneration. In this report, an autosomal recessive neurodevelopmental disorder is proposed, associated with WDR91 loss-of-function in a consanguineous family. The patient presented with severe microcephaly, dysmorphic features, and organomegaly, along with early onset psychomotor delay, hypotonia, sensorineural hearing impairment, and visual impairment. Whole-exome sequencing (WES) identified a homozygous splice site variant, NM_014149.4:c.1395+1G>A, predicted to disrupt the donor site and classified as likely pathogenic (PVS1, PM2). The variant was absent from population databases and our internal in-house cohort. Functional analysis supports a pathogenic role for the variant. WDR91 deficiency results in neuronal loss, cortical thinning, and impaired brain development, as evidenced in Wdr91 knockout models. Our study expands the clinical and genetic spectrum of WDR91-related disorders and highlights the need for further investigations to elucidate the precise molecular mechanisms underlying WDR91-associated pathogenesis.