ABSTRACT
Rare genetic disorders are often challenging to diagnose. Anomalies of tooth number, shape, size, mineralized tissue structure, eruption, and resorption may exist as isolated symptoms or diseases but are often part of the clinical synopsis of numerous syndromes (Bloch-Zupan A, Sedano H, Scully C. Dento/oro/craniofacial anomalies and genetics, 1st edn. Elsevier, Boston, MA, 2012). Concerning amelogenesis imperfecta (AI), for example, mutations in a number of genes have been reported to cause isolated AI, including AMELX, ENAM, KLK4, MMP20, FAM83H, WDR72, C4orf26, SLC24A4, and LAMB3. In addition, many other genes such as DLX3, CNNM4, ROGDI, FAM20A, STIM1, ORAI1, and LTBP3 have been shown to be involved in developmental syndromes with enamel defects. The clinical presentation of the enamel phenotype (hypoplastic, hypomineralized, hypomature, or a combination of severities) alone does not allow a reliable prediction of possible causative genetic mutations. Understanding the potential genetic cause(s) of rare diseases is critical for overall health management of affected patient. One effective strategy to reach a genetic diagnosis is to sequence a selected gene panel chosen for a determined range of phenotypes. Here we describe a laboratory protocol to set up a specific gene panel for orodental diseases.
Subject(s)
Craniofacial Abnormalities/genetics , Genetic Variation , High-Throughput Nucleotide Sequencing/methods , Rare Diseases/genetics , Tooth Abnormalities/genetics , Amelogenesis Imperfecta/diagnosis , Amelogenesis Imperfecta/genetics , Craniofacial Abnormalities/diagnosis , DNA/genetics , Equipment Design , High-Throughput Nucleotide Sequencing/instrumentation , Humans , Rare Diseases/diagnosis , Tooth Abnormalities/diagnosisABSTRACT
Ciliopathies represent a wide spectrum of rare diseases with overlapping phenotypes and a high genetic heterogeneity. Among those, IFT140 is implicated in a variety of phenotypes ranging from isolated retinis pigmentosa to more syndromic cases. Using whole-genome sequencing in patients with uncharacterized ciliopathies, we identified a novel recurrent tandem duplication of exon 27-30 (6.7 kb) in IFT140, c.3454-488_4182+2588dup p.(Tyr1152_Thr1394dup), missed by whole-exome sequencing. Pathogenicity of the mutation was assessed on the patients' skin fibroblasts. Several hundreds of patients with a ciliopathy phenotype were screened and biallelic mutations were identified in 11 families representing 12 pathogenic variants of which seven are novel. Among those unrelated families especially with a Mainzer-Saldino syndrome, eight carried the same tandem duplication (two at the homozygous state and six at the heterozygous state). In conclusion, we demonstrated the implication of structural variations in IFT140-related diseases expanding its mutation spectrum. We also provide evidences for a unique genomic event mediated by an Alu-Alu recombination occurring on a shared haplotype. We confirm that whole-genome sequencing can be instrumental in the ability to detect structural variants for genomic disorders.
