The many faces of oral-facial-digital syndrome

Pathogenic RAB34 variants impair primary cilium assembly and cause a novel oral-facial-digital syndrome

Oral-facial-digital syndromes (OFDS) are a group of clinically and genetically heterogeneous disorders characterized by defects in the development of the face and oral cavity along with digit anomalies. Pathogenic variants in over 20 genes encoding ciliary proteins have been found to cause OFDS through deleterious structural or functional impacts on primary cilia. We identified by exome sequencing bi-allelic missense variants in a novel disease-causing ciliary gene RAB34 in four individuals from three unrelated families. Affected individuals presented a novel form of OFDS (OFDS-RAB34) accompanied by cardiac, cerebral, skeletal and anorectal defects. RAB34 encodes a member of the Rab GTPase superfamily and was recently identified as a key mediator of ciliary membrane formation. Unlike many genes required for cilium assembly, RAB34 acts selectively in cell types that use the intracellular ciliogenesis pathway, in which nascent cilia begin to form in the cytoplasm. We find that the protein products of these pathogenic variants, which are clustered near the RAB34 C-terminus, exhibit a strong loss of function. Although some variants retain the ability to be recruited to the mother centriole, cells expressing mutant RAB34 exhibit a significant defect in cilium assembly. While many Rab proteins have been previously linked to ciliogenesis, our studies establish RAB34 as the first small GTPase involved in OFDS and reveal the distinct clinical manifestations caused by impairment of intracellular ciliogenesis.

Oral-Facial-Digital Syndrome Type 1: A Case Report and Review

Oral-facial-digital syndrome type 1 (OFD1), first described by Papillon-Léage in 1954, is transmitted as an X-linked dominant condition and is characterized by a combination of malformations in the face, oral cavity, and digits. Malformations of the brain and polycystic kidney disease are also commonly associated with OFD1. An 11-month-old female presented with multiple tiny whitish papules on her face that had been present since birth. The histopathologic examination was consistent with milium. She also had congenital anomalies, including incomplete cleft palate, bifid tongue, short frenulum, anomalous deformities of both toes, and clino-brachy-syndactyly. Based on the characteristic dysmorphic features of her face, mouth, and hands, a clinical diagnosis of OFD1 was made. Herein, we report a rare case of OFD1 featuring congenital milia, which has not been previously reported in the Korean literature.