Joubert Syndrome with Orofacial Digital Features

Role of gene interactions in the pathophysiology of skeletal dysplasias: A case report in Colombia

BACKGROUND

Genome association studies have shown that gene-gene interactions or epistasis play a crucial role in identifying the etiology, prognosis, and treatment response of many complex diseases beyond their main effects. Skeletal dysplasias are a heterogeneous group of congenital bone and cartilage disorders with a genetic and gen-gen interaction etiology. The current classification of skeletal dysplasias distinguishes 461 diseases in 42 groups, and the incidence of all skeletal dysplasias is more than 1 in every 5000 newborns. The objective is to present the case of a patient with four variants that generates gen-gen interactions in the skeletal dysplasia.

CASE PRESENTATION

A 1-year-old male patient was diagnosed with skeletal dysplasia based on prenatal ultrasound showing micromelia and pyelocalyceal dilation. Postnatal physical examination revealed body disproportion and involvement of other organs and systems.

MATERIALS AND METHODS

A sequencing study and deletions/duplications analysis were performed for 358 candidate genes associated with skeletal dysplasia. The GeneMANIA interface was used to evaluate the expression network of genes associated with each other for the gen-gen interaction.

RESULTS

Four pathogenic variants were obtained two heterozygous variants with pathogenic significance in SLC26A, one heterozygous pathogenic variant in CLCN7 and another heterozygous pathogenic variant in CEP120. The GeneMANIA interface reveals 77.64% physical interactions, 8.01% co-expression, 5.37% prediction, 3.63% co-localization, 2.87% genetic interactions, 1.88% route of action, and 0.60% shared protein domains.

DISCUSSION AND CONCLUSIONS

These results suggest that the interaction between these genes affects the activity of the inorganic anion exchanger, leading to disorganization of collagen fibers, early mineralization, and decreased assembly of fibronectin in the bone extracellular matrix. Identifying gene-gene interactions is a fundamental step in understanding proper cell function and thus understanding the pathophysiology of many complex human diseases, improving diagnosis, and the possibilities of new personalized therapies.

Primary cilia in skeletal development and disease

Primary cilia are non-motile, microtubule-based sensory organelle present in most vertebrate cells with a fundamental role in the modulation of organismal development, morphogenesis, and repair. Here we focus on the role of primary cilia in embryonic and postnatal skeletal development. We examine evidence supporting its involvement in physiochemical and developmental signaling that regulates proliferation, patterning, differentiation and homeostasis of osteoblasts, chondrocytes, and their progenitor cells in the skeleton. We discuss how signaling effectors in mechanotransduction and bone development, such as Hedgehog, Wnt, Fibroblast growth factor and second messenger pathways operate at least in part at the primary cilium. The relevance of primary cilia in bone formation and maintenance is underscored by a growing list of rare genetic skeletal ciliopathies. We collate these findings and summarize the current understanding of molecular factors and mechanisms governing primary ciliogenesis and ciliary function in skeletal development and disease.

Joubert syndrome a rare entity and role of radiology: A case report

Introduction and importance

Case presentation

Clinical discussion

Conclusion

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Joubert syndrome (JS) is rare entity characterized by set of cerebellum and midbrain abnormalities.

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This case study highlighted a 17-month-old baby presented with typical JS features diagnosed radiologically.

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The patient was given multivitamins, and the parents were counseled, educated on other supportive therapies.

Expanding the genetic landscape of oral-facial-digital syndrome with two novel genes

Oral‐facial‐digital syndromes (OFDS) are a heterogeneous and rare group of Mendelian disorders characterized by developmental abnormalities of the oral cavity, face, and digits caused by dysfunction of the primary cilium, a mechanosensory organelle that exists atop most cell types that facilitates organ patterning and growth. OFDS is inherited both in an X‐linked dominant, X‐linked recessive, and autosomal recessive manner. Importantly, though many of the causal genes for OFDS have been identified, up to 40% of OFD syndromes are of unknown genetic basis. Here we describe three children with classical presentations of OFDS including lingual hamartomas, polydactyly, and characteristic facial features found by exome sequencing to harbor variants in causal genes not previously associated with OFDS. We describe a female with hypothalamic hamartoma, urogenital sinus, polysyndactyly, and multiple lingual hamartomas consistent with OFDVI with biallelic pathogenic variants in CEP164, a gene associated with ciliopathy‐spectrum disease, but never before with OFDS. We additionally describe two unrelated probands with postaxial polydactyly, multiple lingual hamartomas, and dysmorphic features both found to be homozygous for an identical TOPORS missense variant, c.29 C>A; (p.Pro10Gln). Heterozygous TOPORS pathogenic gene variants are associated with autosomal dominant retinitis pigmentosa, but never before with syndromic ciliopathy. Of note, both probands are of Dominican ancestry, suggesting a possible founder allele.

Ciliopathies: Coloring outside of the lines

Ciliopathy syndromes are a diverse spectrum of disease characterized by a combination of cystic kidney disease, hepatobiliary disease, retinopathy, skeletal dysplasia, developmental delay, and brain malformations. Though generally divided into distinct disease categories based on the pattern of system involvement, ciliopathy syndromes are known to display certain phenotypic overlap. We performed next-generation sequencing panel testing, clinical exome sequencing, and research-based exome sequencing reanalysis on patients with suspected ciliopathy syndromes with additional features. We identified biallelic pathogenic variants in BBS1 in a child with features of cranioectodermal dysplasia, and biallelic variants in BBS12 in a child with the clinical stigmata of Bardet-Biedl syndrome, but also with anal atresia. We additionally identified biallelic pathogenic variants in WDR35 and DYNC2H1 in children with predominant liver disease and ductal plate malformation without skeletal dysplasia. Our study highlights the phenotypic and genetic diversity of ciliopathy syndromes, the importance of considering ciliopathy syndromes as a disease-spectrum and screening for all associated complications in all patients, and describes exclusive extra-skeletal manifestations in two classical skeletal dysplasia syndromes.

A rare mutant of OFD1 gene responsible for Joubert syndrome with significant phenotype variation

Joubert syndrome (JBTS), a rare genetic disorder resulted from primary cilium defects or basal-body dysfunction, is characterized by agenesis of cerebellar vermis and abnormal brain stem. Both genotypes and phenotypes of JBTS are highly heterogeneous. The identification of pathogenic gene variation is essential for making a definite diagnosis on JBTS. Here, we found that hypoplasia of cerebellar vermis occurred in three male members in a Chinese family. Then, we performed whole exome sequencing to identify a novel missense mutation c.599T > C (p. L200P) in the OFD1 gene which is the candidate gene of X-linked JBTS (JBST10). The following analysis showed that the variant was absent in the 1000 Genomes, ExAC and the 200 female controls; the position 200 Leucine residue was highly conserved across species; the missense variant was predicted to be deleterious using PolyPhen-2, PROVEAN, SIFT and Mutation Taster. The OFD1 expression was heavily lower in the proband and an induced male fetus compared with a healthy male with a wild-type OFD1 gene. The in vitro expression analysis of transiently transfecting c.599T or c.599C plasmids into HEK-293T cells confirmed that the missense mutation caused OFD1 reduction at the protein level. And further the mutated OFD1 decreased the level of Gli1 protein, a read-out of Sonic hedgehog (SHH) signaling essential for development of central neural system. A known pathogenic variant c.515T > C (p. L172P) showed the similar results. All of these observations suggested that the missense mutation causes the loss function of OFD1, resulting in SHH signaling impairs and brain development abnormality. In addition, the three patients have Dandy-Walker malformation, macrogyria and tetralogy of Fallot, respectively, the latter two of which are firstly found in JBTS10 patients. In conclusion, our findings expand the context of genotype and phenotype in the JBTS10 patients.