The Johanson-Blizzard syndrome: report of a new case with special reference to the dentition and review of the literature

We report a new case of Johanson-Blizzard syndrome. The clinical findings with special reference to the dentition are discussed, and the literature is reviewed. The reported case underlines the heterogeneity of ectodermal dysplasias mentioned by Freire-Maia (1971).     

The conditions manifesting taurodontism

Taurodontism is a trait that has captured the interests of evolutionists and clinical geneticists. This paper reviews the reported cases of taurodontism as an isolated trait and as a component of malformation syndromes. Because of the nature of the syndromes with which it is associated and its frequency in the general population, it is concluded that taurodontism is the result of an ectodermal defect and may be useful as an indicator of development instability.     

A mutation in the hair matrix and cuticle keratin KRTHB5 gene causes ectodermal dysplasia of hair and nail type

Background

Ectodermal dysplasias are developmental disorders affecting tissues of ectodermal origin. To date, four different types of ectodermal dysplasia involving only hair and nails have been described. In an effort to understand the molecular bases of this form of ectodermal dysplasia, large Pakistani consanguineous kindred with multiple affected individuals has been ascertained from a remote region in Pakistan.

Objective

To identify the gene underlying the phenotype.

Methods

Microsatellite markers were genotyped in candidate regions and two point and multipoint parametric linkage analysis carried out.

Results

The disease locus was mapped to a 16.6 centimorgan region on chromosome 12q12–q14.1 (Z_max = 8.2), which harbours six type II hair keratin genes. DNA sequence analysis revealed a homozygous missense mutation in the hair matrix and cuticle keratin KRTHB5, leading to histidine substitution of a conserved arginine residue (R78H) located in the head domain.

Conclusions

This report provides the first direct evidence relating to the molecular pathogenesis of pure hair–nail ectodermal dysplasias.     

Skeletal dysplasias and the growth plate

Skeletal dysplasias are disorders in which there is derangement in the growth or shape of the skeleton. Long bone grows from cartilage that persists near the ends until skeletal maturity as the growth plate. Developmental biology work has identified the major regulatory proteins in growth plate chondroyte function. There are hundreds of skeletal dysplasias, and the molecular genetic etiology of many was defined in the past decade and a half. Now that the causative genes for these disorders have been identified, they can be broadly classified by the function of the protein that these genes encode for into disorders caused by extracellular structural proteins, proteins that regulate normal growth plate chondrocyte differentiation and patterning, and enzymes that process these proteins. There are clinical similarities within each group, and the phenotype can be predicted based on the role of the mutated protein in normal growth plate function. As such, this framework to classify the skeletal dysplasias has practical clinical implications.     

Ectodermal dysplasias: not only 'skin' deep

The ectodermal dysplasias (EDs) are a large and complex nosologic group of diseases; more than 170 different pathologic clinical conditions have been identified. Despite the great number of EDs described so far, few causative genes have been identified. We review EDs in the light of the most recent molecular findings and propose a new classification of EDs integrating both molecular-genetic data and corresponding clinical findings of related diseases.     

Neurologic abnormalities in the skeletal dysplasias: A clinical and radiological perspective

The neurologic manifestations of the skeletal dysplasias are reviewed. Three important major groups are identified: Achondroplasia (cranio-cervical junction problems in infancy, spinal stenosis and neurogenic claudication in the adult). Type II collagenopathies (upper cervical spine anatomic and functional problems), and craniotubular and sclerosing bone dysplasias (osseous overgrowth with foraminal obstruction problems). The remainder of the well-identified 150 or so bone dysplasias are also evaluated in depth for their diverse neurologic abnormalities. The findings discussed are important both for the diagnosis and management of these patients. Am. J. Med. Genet. 69:33–43, 1997. © 1997 Wiley-Liss, Inc.     

Ectodermal dysplasias: a new clinical-genetic classification

The ectodermal dysplasias (EDs) are a large and complex nosological group of diseases, first described by Thurnam in 1848. In the last 10 years more than 170 different pathological clinical conditions have been recognised and defined as EDs, all sharing in common anomalies of the hair, teeth, nails, and sweat glands. Many are associated with anomalies in other organs and systems and, in some conditions, with mental retardation.The anomalies affecting the epidermis and epidermal appendages are extremely variable and clinical overlap is present among the majority of EDs. Most EDs are defined by particular clinical signs (for example, eyelid adhesion in AEC syndrome, ectrodactyly in EEC). To date, few causative genes have been identified for these diseases. We recently reviewed genes known to be responsible for EDs in light of their molecular and biological function and proposed a new approach to EDs, integrating both molecular-genetic data and corresponding clinical findings. Based on our previous report, we now propose a clinical-genetic classification of EDs, expand it to other entities in which no causative genes have been identified based on the phenotype, and speculate on possible candidate genes suggested by associated "non-ectodermal" features.     

Fetal skeletal dysplasia cohort of a single tertiary referral center in Istanbul,Turkey

We report on 314 fetal cases from 297 unrelated families with skeletal dysplasia evaluated in the postmortem period from 2000 to 2017 at a single clinical genetics center in İstanbul, Turkey. The definite diagnostic yield was 40% during the prenatal period, while it reached 74.5% when combined with postmortem clinical and radiological evaluation. Molecular analyses were performed in 25.5% (n: 76) of families, and 21 novel variants were identified. Classification according to International Skeletal Dysplasia Society-2019 revision revealed limb hypoplasia-reduction defects group (39) as the leading one, 24.5%, then followed by FGFR3 chondrodysplasias, osteogenesis imperfecta, and decreased mineralization and polydactyly-syndactyly-triphalangism groups 13.6, 11.1, and 8.9%, respectively. The inheritance pattern was autosomal recessive in 54% and autosomal dominant in 42.6% of index cases. The overall consanguinity rate of the cohort was 33%. The high prevalence of ultrarare diseases along with two or more unrelated autosomal recessive entities running in the same family was noteworthy. This study highlights the pivotal role of postmortem evaluation by an experienced clinical geneticist to achieve a high diagnostic yield in fetal skeletal dysplasia cohorts. The cohort is not only a representation of the spectrum of skeletal dysplasias in a population with a high consanguinity rate but also provides an ideal research group to work on to identify the unknowns of early fetal life.     

WNT10A gene is the second molecular candidate in a cohort of young Italian subjects with ectodermal derivative impairment (EDI)

Ectodermal dysplasias are a group of genetic disorders defined by ectodermal derivative impairment (EDI). To test the impact of the Wnt/beta‐catenin pathway in the genetic screening of EDI, we performed a molecular gene study of WNT10A in 60 subjects from a population of 133 young Italian patients referred for the impairment of at least one major ectodermal‐derived structure and who had a previous negative molecular screen for ectodysplasin signaling pathway genes ED1, EDAR, and EDARADD. Fourteen WNT10A mutations were identified in 33 subjects (24.8%), 11 of which were novel variants. The phenotype was evaluated through a detailed clinical examination of the major and minor ectodermal‐derived structures. This study is the first to show that, after ED1, WNT10A is the second molecular candidate for EDI in a large Italian Caucasian population. The study confirmed that Phe228Ile is the most frequent WNT10A variant in Caucasian populations, and that WNT10A mutations are associated with large variability in EDI.     

Ectodermal dysplasias: Classification and organization by phenotype,genotype and molecular pathway

An international advisory group met at the National Institutes of Health in Bethesda, Maryland in 2017, to discuss a new classification system for the ectodermal dysplasias (EDs) that would integrate both clinical and molecular information. We propose the following, a working definition of the EDs building on previous classification systems and incorporating current approaches to diagnosis: EDs are genetic conditions affecting the development and/or homeostasis of two or more ectodermal derivatives, including hair, teeth, nails, and certain glands. Genetic variations in genes known to be associated with EDs that affect only one derivative of the ectoderm (attenuated phenotype) will be grouped as non‐syndromic traits of the causative gene (e.g., non‐syndromic hypodontia or missing teeth associated with pathogenic variants of EDA “ectodysplasin”). Information for categorization and cataloging includes the phenotypic features, Online Mendelian Inheritance in Man number, mode of inheritance, genetic alteration, major developmental pathways involved (e.g., EDA, WNT “wingless‐type,” TP63 “tumor protein p63”) or the components of complex molecular structures (e.g., connexins, keratins, cadherins).     

Sclerosteosis: report of a case in a black African man

Sclerosteosis is a rare genetic disorder of bone modelling, similar to, but distinct from, van Buchem disease; it has been described almost exclusively in Afrikaners of South Africa, a white population of Dutch ancestry. Isolated cases have been reported in a girl in Japan, a boy in Spain, and in multiracial families in Brazil and USA.
Here we report a case of sclerosteosis in a black man born in Senegal. He presented with the full features of the disease: tall stature; syndactyly; nail dysplasia; massive sclerosis of the long tubular bones, the ribs, the pelvis and the skull; multiple cranial nerve involvement: optic atrophy, facial palsy and trigeminal neuralgia. Radiologic examination, visual and brainstem auditory evoked potentials, computerized tomography and magnetic resonance imaging of the skull were performed. This seems to be the first case of the disease in a black African individual, with no known relationship with Dutch ancestry.     

X-linked hypohidrotic ectodermal dysplasia and t(X;12) in a female

A female patient with features of hypohidrotic ectodermal dysplasia (HED) was found to be a carrier of a de novo t(X;12) with a breakpoint in Xq13.1. This is the second instance of an X/autosome translocation, with apparently the same X breakpoint, reported in HED.     

X连锁隐性遗传性少汗性外胚层发育不全一家系EDA基因突变分析

目的 对1个X连锁隐性遗传性少汗性外胚层发育不全(X-linked hypohidrotic ectodermal dysplasia,XLHED)家系进行EDA基因检测,分析基因突变类型,探讨其遗传学因素及发病原因.方法 对该XLHED家系进行家系调查,收集家系患者及部分成员和50名无亲缘关系的正常个体的外周血标本并提取基因组DNA,应用聚合酶链反应扩增EDA基因8个外显子,DNA直接测序进行突变检测.结果 该家系中患者检出EDA基因第3外显子存在c.467G＞A突变,导致R156H错义突变.先证者的母亲及姨妈携带c.467G＞A杂合突变,家系中正常个体和正常对照个体均未检测到该突变.结论 EDA基因的R156H突变可能是引起该XLHED家系先证者少汗性外胚层发育不全的致病原因.     

New form of hidrotic ectodermal dysplasia in a Lebanese family

We report a sister and brother born to consanguineous parents presenting with severe hypodontia, fine hair, and onychodysplasia. Five other relatives are similarly affected. The comparison with other ectodermal dysplasias is presented and discussed. The possibility of a new autosomal recessive form of ectodermal dysplasia is raised. Am. J. Med. Genet. 75:196–199, 1998. © 1998 Wiley-Liss, Inc.