Joint dislocation and cerebral anomalies are consistently associated with oral-facial-digital syndrome type IV

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.

Craniodentofacial Manifestations in a Rare Syndrome: Orofaciodigital Type IV (Mohr-Majewski Syndrome)

Background. The orofaciodigital syndromes (OFDS) are a heterogeneous group of syndromes that affect the face, oral cavity, and the digits. OFDS type IV (OMIM %258860) is rare and characterized by broad nasal root and tip, orbital hypertelorism or telecanthus, micrognathia, hypoplastic mandible, and low-set ears. Oral symptoms may include cleft lip, cleft or highly arched palate, bifid uvula, cleft or hypoplastic maxillary and mandibular alveolar ridge, oral frenula, lingual hamartoma, and absent or hypoplastic epiglottis. Dental anomalies are common and generally include disturbances in the number of teeth. Case Report. This report presents a six-year-old girl, referred with the chief complaint of missing teeth. She was diagnosed as having OFDS type IV based on clinical findings. Her parents reported three deceased children and two fetuses that had the same phenotype. She was the seventh child of consanguineous parents who were first cousins. Conclusion. This is a very rare syndrome. Many reported OFDS type IV cases have consanguineous parents, consistent with an autosomal recessive trait. Manifestation of cleft palate in the healthy sibling may be mild expression of the disorder or an unrelated isolated cleft.

Compound heterozygosity for a frame shift mutation and a likely pathogenic sequence variant in the planar cell polarity—ciliogenesis gene WDPCP in a girl with polysyndactyly, coarctation of the aorta, and tongue hamartomas

We report on a young girl with polysyndactyly, coarctation of the aorta, and tongue hamartomas. These features are similar to those reported in individuals with variant forms of orofaciodigital syndrome known as congenital heart defects, hamartomas of the tongue and polysyndactly (CHDHTP: OMIM 217085) [Örstavik et al., 1992] and orocardiodigital syndrome [Digilio et al., 1996]. Whole exome sequencing revealed that she is a compound heterozygote for a frame shift mutation and a likely pathogenic sequence variant in WDPCP, a gene that regulates planar cell polarity and ciliogenesis. Results of genotyping in her parents and unaffected siblings were consistent with autosomal recessive inheritance of the mutation and the WDPCP variant. These results suggest that disruption of planar cell polarity and ciliogenesis may result in this unusual form of orofaciodigital syndrome.

TCTN3 mutations cause Mohr-Majewski syndrome

Orofaciodigital syndromes (OFDSs) consist of a group of heterogeneous disorders characterized by abnormalities in the oral cavity, face, and digits and associated phenotypic abnormalities that lead to the delineation of 13 OFDS subtypes. Here, by a combined approach of homozygozity mapping and exome ciliary sequencing, we identified truncating TCTN3 mutations as the cause of an extreme form of OFD associated with bone dysplasia, tibial defect, cystic kidneys, and brain anomalies (OFD IV, Mohr-Majewski syndrome). Analysis of 184 individuals with various ciliopathies (OFD, Meckel, Joubert, and short rib polydactyly syndromes) led us to identify four additional truncating TCTN3 mutations in unrelated fetal cases with overlapping Meckel and OFD IV syndromes and one homozygous missense mutation in a family with Joubert syndrome. By exploring roles of TCTN3 in human ciliary related functions, we found that TCTN3 is necessary for transduction of the sonic hedgehog (SHH) signaling pathway, as revealed by abnormal processing of GLI3 in patient cells. These results are consistent with the suggested role of its murine ortholog, which forms a complex at the ciliary transition zone with TCTN1 and TCTN2, both of which are also implicated in the transduction of SHH signaling. Overall, our data show the involvement of the transition zone protein TCTN3 in the regulation of the key SHH signaling pathway and that its disruption causes a severe form of ciliopathy, combining features of Meckel and OFD IV syndromes.

Oro-facial-digital syndrome IX with severe microcephaly: a new variant in a genetically isolated population

We describe four patients, two pairs of siblings, with a somewhat unique oro-facial-digital syndrome. The siblings come from the Navajo population which has undergone several genetic "bottlenecks." Thus, as would be anticipated, this syndrome seems to show autosomal recessive inheritance. The combination of the presence of retinal colobomata and the paucity of digital findings in these patients leads us to believe that their condition is best described as a variant of oro-facial-digital syndrome IX. In addition to retinal colobomata, these patients also show severe microcephaly, mental retardation and short stature.

Oral-facial-digital syndromes: review and diagnostic guidelines

The oral-facial-digital syndromes (OFDS) result from the pleiotropic effect of a morphogenetic impairment affecting almost invariably the mouth, face and digits. Other organ systems can be involved, defining specific types of OFDS. To date, 13 types have been distinguished based on characteristic clinical manifestations. An updated list of these types is provided and recent molecular data are discussed.

Orocardiodigital syndrome: an oral-facial-digital type II variant associated with atrioventricular canal

We report on a patient with a constellation of anomalies including hamartomas of the tongue, polysyndactyly, and atrioventricular canal. A similar association has been previously described by Orstavik et al in two sibs. The clinical spectrum of the oralfacial-digital syndrome (OFDS) type II includes all these features. In particular, congenital heart defect, mainly atrioventricular canal, has been described in a few cases. It has been previously suggested that these latter patients may be affected by a variant of OFDS type II. We propose to distinguish this orocardiodigital variant and point out the association of the syndrome with atrioventricular canal.