Ectodermal Dysplasia Panel

Ectodermal Dysplasia (ED) is a group of closely related conditions of which more than 150 different syndromes have been identified. EDs affects the development or function of teeth, hair, nails and sweat glands. ED may present as isolated or as part of a syndromic disease and is commonly subtyped according to sweating ability. The clinical features of the X-linked and autosomal forms of hypohidrotic ectodermal dysplasia (HED) can be indistinguishable and many of the involved genes may lead to phenotypically distinct outcomes depending on number of defective alleles. The most common EDs are hypohidrotic ED and hydrotic ED. X-linked hypohidrotic ectodermal dysplasia (HED) is caused by EDA mutations and explain 75%-95% of familial HED and 50% of sporadic cases. HED is characterized by three cardinal features: hypotrichosis (sparse, slow-growing hair and sparse/missing eyebrows), reduced sweating and hypodontia (absence or small teeth). Reduced sweating poses risk for episodes of hyperthermia. Female carriers may have some degree of hypodontia and mild hypotrichosis. Isolated dental phenotypes have also been described. Mutations in WNT10A have been reported in up to 9% of individuals with HED and in 25% of individuals with HED who do not have defective EDA. Approximately 50% of individuals with heterozygous WNT10A mutation have HED and the most consistent clinical feature is severe oligodontia of permanent teeth. Mutations in EDAR explain 7% of HED and are associated with both autosomal dominant and recessive ED. This panel provide differential diagnostic power as it covers many syndromes that may present with ED. Several syndromes characterized by ED and hearing loss are associated with GJB2 mutations including KID syndrome, Vohwinkel syndrome, Bart-Pumphrey syndrome. Hidrotic ED type 2 is caused by autosomal dominant GJB6 mutations and characterized by hypotrichosis, dysplastic nails and palmoplantar hyperkeratosis. Unlike other ectodermal dysplasias, sweating and tooth development are normal. Recessive EVC and EVC2 mutations cause Ellis-van Creveld syndrome characterized by ED, dwarfism, polydactyly and heart defects, however, dominant mutations in the same genes cause the less severe Weyers acrofacial dysostosis. Expression of DSP-related ED is variable including woolly hair, alopecia, hyperkeratotic plaques, failure to thrive, dilated and arrhythmogenic right ventricular cardiomyopathy. The most severe presentation is lethal acantholytic epidermolysis bullosa. The prevalence of HED is estimated to be 1:5,000-10,000 newborns while that of Ellis-van Creveld syndrome is 1:60,000 – 200,000.

The target region for each gene includes coding exons and ±20 base pairs from the exon-intron boundary. In addition, the panel includes non-coding and regulatory variants if listed above (Non-coding variants covered by the panel). Some regions of the gene(s) may be removed from the panel if specifically mentioned in the ‘Test limitations” section above. If the test includes the mitochondrial genome the target region gene list contains the mitochondrial genes. The sequencing data generated in our laboratory is analyzed with our proprietary data analysis and annotation pipeline, integrating state-of-the art algorithms and industry-standard software solutions. Incorporation of rigorous quality control steps throughout the workflow of the pipeline ensures the consistency, validity and accuracy of results. Our pipeline is streamlined to maximize sensitivity without sacrificing specificity. We have incorporated a number of reference population databases and mutation databases including, but not limited, to 1000 Genomes Project, gnomAD, ClinVar and HGMD into our clinical interpretation software to make the process effective and efficient. For missense variants, in silico variant prediction tools such as  SIFT, PolyPhen,MutationTaster are used to assist with variant classification. Through our online ordering and statement reporting system, Nucleus, ordering providers have access to the details of the analysis, including patient specific sequencing metrics, a gene level coverage plot and a list of regions with suboptimal coverage (<20X for nuclear genes and <1000X for mtDNA) if applicable. This reflects our mission to build fully transparent diagnostics where ordering providers can easily visualize the crucial details of the analysis process.

We provide customers with the most comprehensive clinical report available on the market. Clinical interpretation requires a fundamental understanding of clinical genetics and genetic principles. At Blueprint Genetics, our PhD molecular geneticists, medical geneticists, and clinical consultants prepare the clinical statement together by evaluating the identified variants in the context of the phenotypic information provided in the requisition form. Our goal is to provide clinically meaningful statements that are understandable for all medical professionals regardless of whether they have formal training in genetics.

Variant classification is the cornerstone of clinical interpretation and resulting patient management decisions. Our classifications follow the ACMG guideline 2015.

The final step in the analysis is orthogonal confirmation. Sequence and copy number variants classified as pathogenic, likely pathogenic, and variants of uncertain significance (VUS) are confirmed using bi-directional Sanger sequencing or by orthogonal methods such as qPCR/ddPCR when they do not meet our stringent NGS quality metrics for a true positive call.

Our clinical statement includes tables for sequencing and copy number variants that include basic variant information (genomic coordinates, HGVS nomenclature, zygosity, allele frequencies, in silico predictions, OMIM phenotypes, and classification of the variant). In addition, the statement includes detailed descriptions of the variant, gene, and phenotype(s) including the role of the specific gene in human disease, the mutation profile, information about the gene’s variation in population cohorts, and detailed information about related phenotypes. We also provide links to the references, abstracts, and variant databases used to help ordering providers further evaluate the reported findings if desired. The conclusion summarizes all of the existing information and provides our rationale for the classification of the variant.

Identification of pathogenic or likely pathogenic variants in dominant disorders or their combinations in different alleles in recessive disorders are considered molecular confirmation of the clinical diagnosis. In these cases, family member testing can be used for risk stratification. We do not recommend using variants of uncertain significance (VUS) for family member risk stratification or patient management. Genetic counseling is recommended.

Our interpretation team analyzes millions of variants from thousands of individuals with rare diseases. Our internal database and our understanding of variants and related phenotypes increases with every case analyzed. Our laboratory is therefore well-positioned to re-classify previously reported variants as new information becomes available. If a variant previously reported by Blueprint Genetics is re-classified, our laboratory will issue a follow-up statement to the original ordering healthcare provider at no additional cost, according to our latest follow-up reporting policy.