Charcot-Marie-Tooth Neuropathy Panel

Charcot-Marie-Tooth (CMT) neuropathy, also known as hereditary motor/sensory neuropathy (HMSN) is the most common genetic cause of neuropathy. Prevalence is estimated to be 1:3,300. CMT is characterized by broad genetic heterogeneity and can be inherited in an autosomal dominant, autosomal recessive or X-linked manner. CMT neuropathy results from involvement of peripheral nerves that can affect the motor system and/or the sensory system. Individuals with CMT experience symmetric, slowly progressive distal motor neuropathy of the arms and legs usually beginning in the first to third decade of life, and resulting in weakness and atrophy of the muscles in the feet and/or hands. Pes cavus foot deformity is common. CMT neuropathies can be divided to demyelinating and axonal forms.

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 comprehensive clinical report available on the market. Clinical interpretation requires a fundamental understanding of clinical genetics and genetic principles. At Blueprint Genetics, our Ph.D. molecular geneticists, medical professionals, and other highly experienced experts prepare clinical reports by evaluating the identified variants in the context of the phenotypic information provided in the requisition form.

Our goal is to provide clinically meaningful reports 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. Sequence and copy number variants classified as pathogenic, likely pathogenic, and variants of uncertain significance (VUS) are confirmed using bidirectional 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 report includes tables for sequence and copy number variants that include basic variant information (genomic coordinates, HGVS nomenclature, zygosity, allele frequencies, in silico predictions, 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 panel report is divided into primary findings and additional findings sections. Variants reported as primary findings are known disease-causing variants or rare variants that could potentially explain the patient’s phenotype as described to the laboratory at the time of interpretation. The conclusion summarizes all the existing information and provides our rationale for the classification of the variant.

Variants reported as additional findings are variants that are not likely or sufficient to cause the tested patient’s phenotype, based on the current knowledge. Additional findings in panel reports include variants that are, for example, carrierships of single heterozygous variants in genes associated with autosomal recessive disorders, variants of uncertain significance in genes associated with autosomal dominant disorders (if pathogenic or likely pathogenic variants considered sufficient to explain the patient’s phenotype are reported as primary findings), or risk alleles identified in genes included in the panel.

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 reclassify previously reported variants as new information becomes available. If a variant previously reported as a primary or secondary finding by Blueprint Genetics is reclassified so that it becomes diagnostic (VUS to P/LP) or earlier molecular diagnosis is removed (P/LP to VUS, LB, B), our laboratory will issue a follow-up statement to the original ordering healthcare provider at no additional cost.