Molecular Pathway-Based Classification of Ectodermal Dysplasias: First Five-Yearly Update.

To keep pace with the rapid advancements in molecular genetics and rare diseases research, we have updated the list of ectodermal dysplasias based on the latest classification approach that was adopted in 2017 by an international panel of experts. For this purpose, we searched the databases PubMed and OMIM for the term "ectodermal dysplasia", referring mainly to changes in the last 5 years. We also tried to obtain information about those diseases on which the last scientific report appeared more than 15 years ago by contacting the authors of the most recent publication. A group of experts, composed of researchers who attended the 8th International Conference on Ectodermal Dysplasias and additional members of the previous classification panel, reviewed the proposed amendments and agreed on a final table listing all 49 currently known ectodermal dysplasias for which the molecular genetic basis has been clarified, including 15 new entities. A newly reported ectodermal dysplasia, linked to the gene LRP6, is described here in more detail. These ectodermal dysplasias, in the strict sense, should be distinguished from syndromes with features of ectodermal dysplasia that are related to genes extraneous to the currently known pathways involved in ectodermal development. The latter group consists of 34 syndromes which had been placed on the previous list of ectodermal dysplasias, but most if not all of them could actually be classified elsewhere. This update should streamline the classification of ectodermal dysplasias, provide guidance to the correct diagnosis of rare disease entities, and facilitate the identification of individuals who could benefit from novel treatment options.

Further evidence for specific IFIH1 mutation as a cause of Singleton-Merten syndrome with phenotypic heterogeneity.

Singleton-Merten syndrome (MIM 182250) is an autosomal dominant inherited disorder characterized by early onset periodontitis, root resorption, osteopenia, osteoporosis, and aortic valve or thoracic aorta calcification. The disorder can have significant intrafamilial phenotypic variability. Here, we present a mother and daughter with Singleton-Merten syndrome harboring a previously described pathogenic missense mutation, c.2465G>A p.(Arg822Gln), in IFIH1 (interferon induced with helicase C domain 1), encoding MDA5 (Melanoma Differentiation-Associated protein 5). These data confirm the pathogenicity of IFIH1 c.2465G>A p.(Arg822Gln) for Singleton-Merten syndrome and affirm the striking phenotypic heterogeneity of this disorder. In addition, we expand the Singleton-Merten phenotype by adding severe systemic lupus erythematosus (SLE) to the clinical picture. Investigations of known SLE genes as well as a single nucleotide polymorphism suggested to be involved in development of SLE were normal.

Abnormal primary and permanent dentitions with ectodermal symptoms predict WNT10A deficiency.

BACKGROUND: The WNT10A protein is critical for the development of ectodermal appendages. Variants in the WNT10A gene may be associated with a spectrum of ectodermal abnormalities including extensive tooth agenesis. METHODS: In seven patients with severe tooth agenesis we identified anomalies in primary dentition and additional ectodermal symptoms, and assessed WNT10A mutations by genetic analysis. RESULTS: Investigation of primary dentition revealed peg-shaped crowns of primary mandibular incisors and three individuals had agenesis of at least two primary teeth. The permanent dentition was severely affected in all individuals with a mean of 21 missing teeth. Primary teeth were most often present in positions were succedaneous teeth were missing. Furthermore, most existing molars had taurodontism. Light, brittle or coarse hair was reported in all seven individuals, hyperhidrosis of palms and soles in six individuals and nail anomalies in two individuals. The anomalies in primary dentition preceded most of the additional ectodermal symptoms. Genetic analysis revealed that all seven individuals were homozygous or compound heterozygous for WNT10A mutations resulting in C107X, E222X and F228I. CONCLUSIONS: We conclude that tooth agenesis and/or peg-shaped crowns of primary mandibular incisors, severe oligodontia of permanent dentition as well as ectodermal symptoms of varying severity may be predictors of bi-allelic WNT10A mutations of importance for diagnosis, counselling and follow-up.

Hypoplastic root cementum and premature loss of primary teeth in Coffin-Lowry syndrome: a case report.

BACKGROUND: Coffin-Lowry syndrome (CLS) is a rare genetic disorder. The syndrome presents with psychomotor retardation, short stature, skeletal deformations, digit abnormalities, and distinctive facial features. Oral and dental findings in CLS are common and they include thick prominent lips, high palate, midline lingual furrow, hypodontia, microdontia, delayed eruption, and early tooth loss. Only one earlier case suggesting hypoplastic root cementum as cause for primary loss of teeth in CLS has been published. CASE REPORT: This case describes a 3-year-old boy with premature loss of primary incisors without preceding root resorption. In addition to the dental findings, the boy had several general signs and symptoms and the dental findings together with the other characteristics led to the clinical diagnosis of CLS, which later was genetically verified. Histological analysis of an extracted primary incisor showed hypoplastic root cementum. CONCLUSION: Hypoplastic root cementum may explain early tooth loss in CLS. As early loss of primary teeth is rare, especially when there is no previous root resorption, the individual is likely to seek dental care. Thus, the dentist may play an important role in assisting in the diagnosing of CLS.

Isolated oligodontia associated with mutations in EDARADD, AXIN2, MSX1, and PAX9 genes.

Oligodontia is defined as the congenital lack of six or more permanent teeth, excluding third molars. Oligodontia as well as hypodontia (lack of one or more permanent teeth) are highly heritable conditions associated with mutations in the AXIN2, MSX1, PAX9, EDA, and EDAR genes. Here we define the prevalence of mutations in the AXIN2, MSX1, PAX9, EDA, and EDAR genes, and the novel candidate gene EDARADD in a cohort of 93 Swedish probands with non-syndromic, isolated oligodontia. Mutation screening was performed using denaturing gradient gel electrophoresis and DNA sequence analysis. Analyses of the coding sequences of the six genes showed sequence alterations predicted to be damaging or potentially damaging in ten of 93 probands (10.8%). Mutations were identified in the EDARADD (n = 1), AXIN2 (n = 3), MSX1 (n = 2), and PAX9 (n = 4) genes, respectively. None of the 10 probands with mutations had other self-reported symptoms from ectodermal tissues. The oral parameters were similar when comparing individuals with and without mutations but a family history of oligodontia was three times more frequent for probands with mutations. EDARADD mutations have previously been reported in a few families segregating hypohidrotic ectodermal dysplasia and this is, to our knowledge, the first report of an EDARADD mutation associated with isolated oligodontia.