BackgroundOrodental diseases include several clinically and genetically heterogeneous disorders that can present in isolation or as part of a genetic syndrome. Due to the vast number of genes implicated in these disorders, establishing a molecular diagnosis can be challenging. We aimed to develop a targeted next-generation sequencing (NGS) assay to diagnose mutations and potentially identify novel genes mutated in this group of disorders.MethodsWe designed an NGS gene panel that targets 585 known and candidate genes in orodental disease. We screened a cohort of 101 unrelated patients without a molecular diagnosis referred to the Reference Centre for Oro-Dental Manifestations of Rare Diseases, Strasbourg, France, for a variety of orodental disorders including isolated and syndromic amelogenesis imperfecta (AI), isolated and syndromic selective tooth agenesis (STHAG), isolated and syndromic dentinogenesis imperfecta, isolated dentin dysplasia, otodental dysplasia and primary failure of tooth eruption.ResultsWe discovered 21 novel pathogenic variants and identified the causative mutation in 39 unrelated patients in known genes (overall diagnostic rate: 39%). Among the largest subcohorts of patients with isolated AI (50 unrelated patients) and isolated STHAG (21 unrelated patients), we had a definitive diagnosis in 14 (27%) and 15 cases (71%), respectively. Surprisingly, COL17A1 mutations accounted for the majority of autosomal-dominant AI cases.ConclusionsWe have developed a novel targeted NGS assay for the efficient molecular diagnosis of a wide variety of orodental diseases. Furthermore, our panel will contribute to better understanding the contribution of these genes to orodental disease.Trial registration numbersNCT01746121 and NCT02397824.

While Friedreich's ataxia (FRDA) and ataxia telangiectasia (AT) are known to be the two most frequent forms of autosomal recessive cerebellar ataxia (ARCA), knowledge on the other forms of ARCA has been obtained only recently, and they appear to be rarer. Little is known about the epidemiological features and the relative frequency of the ARCAs and only few data are available about the comparative features of ARCAs. We prospectively studied 102 suspected ARCA cases from Eastern France (including 95 from the Alsace region) between 2002 and 2008. The diagnostic procedure was based on a sequential strategic scheme. We examined the clinical, paraclinical and molecular features of the large cohort of patients and compared features and epidemiology according to molecular diagnosis. A molecular diagnosis could be established for 57 patients; 36 were affected with FRDA, seven with ataxia plus oculomotor apraxia type 2 (AOA2), four with AT, three with ataxia plus oculomotor apraxia type 1 (AOA1), three with Marinesco-Sjögren syndrome, two with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), one with ataxia with vitamin E deficiency (AVED) and one with autosomal recessive cerebellar ataxia type 2 (ARCA2). The group of patients with no identified mutation had a significantly lower spinocerebellar degeneration functional score corrected for disease duration (SDFS/DD ratio; p = 0.002) and comprised a significantly higher proportion of cases with onset after 20 years (p < 0.01). Extensor plantar reflexes were rarer and cerebellar atrophy was more frequent in the group of patients with a known non-Friedreich ARCA compared to all other patients (p < 0.0001 and p = 0.0003, respectively). Lower limb areflexia and electroneuromyographic evidences of peripheral neuropathy were more frequent in the Friedreich ataxia group than in the group with a known non-Friedreich ataxia and were more frequent in the later group than in the group with no identified mutation (p = 0.0001 and p = 0.01, respectively). The overall prevalence of ARCA in Alsace is 1/19,000. We can infer the prevalence of FRDA in Alsace to be 1/50,000 and infer that AT is approximately eight times less frequent than FRDA. MSS, AOA2 and ARSACS appear only slightly less frequent than AT. Despite the broad variability of severity, Friedreich ataxia patients are clinically distinct from the other forms of ARCA. Patients with no identified mutation have more often a pure cerebellar degenerative disease or a spastic ataxia phenotype. It appears that ARCA cases can be divided into two major groups of different prognosis, an early-onset group with a highly probable genetic cause and an adult-onset group with better prognosis for which a genetic cause is more difficult to prove but not excluded. ARCAs are rare, early-disabling and genetically heterogeneous diseases dominated by FRDA. Several of the recently identified ARCAs, such as AVED, ARSACS, AOA1, AOA2 and MSS, have a prevalence close to AT and should be searched for extensively irrespective of ethnic orig...

Background/Aims: Calcium homeostasis requires regulated cellular and interstitial systems interacting to modulate the activity and movement of this ion. Disruption of these systems in the kidney results in nephrocalcinosis and nephrolithiasis, important medical problems whose pathogenesis is incompletely understood. Methods: We investigated 25 patients from 16 families with unexplained nephrocalcinosis and characteristic dental defects (amelogenesis imperfecta, gingival hyperplasia, impaired tooth eruption). To identify the causative gene, we performed genome-wide linkage analysis, exome capture, next-generation sequencing, and Sanger sequencing. Results: All patients had bi-allelic FAM20A mutations segregating with the disease; 20 different mutations were identified. Conclusions: This au-tosomal recessive disorder, also known as enamel renal syndrome, of FAM20A causes nephrocalcinosis and amelogenesis imperfecta. We speculate that all individuals with biallelic FAM20A mutations will eventually show nephrocalcinosis.

Holoprosencephaly (HPE) is the most common congenital cerebral malformation in humans, characterized by impaired forebrain cleavage and midline facial anomalies. It presents a high heterogeneity, both in clinics and genetics. We have developed a novel targeted next-generation sequencing (NGS) assay and screened a cohort of 257 HPE patients. Mutations with high confidence in their deleterious effect were identified in approximately 24% of the cases and were held for diagnosis, whereas variants of uncertain significance were identified in 10% of cases. This study provides a new classification of genes that are involved in HPE. SHH, ZIC2, and SIX3 remain the top genes in term of frequency with GLI2, and are followed by FGF8 and FGFR1. The three minor HPE genes identified by our study are DLL1, DISP1, and SUFU. Here, we demonstrate that fibroblast growth factor signaling must now be considered a major pathway involved in HPE. Interestingly, several cases of double mutations were found and argue for a polygenic inheritance of HPE. Altogether, it supports that the implementation of NGS in HPE diagnosis is required to improve genetic counseling.

We have expanded the clinical spectrum of autosomal recessive variants by describing a syndrome with features overlapping CS/CISS1 and BOS.