Primary Immunodeficiency (PID) and Primary Ciliary Dyskinesia (PCD) Panel

Primary immunodeficiencies (PIDs) are a genetically heterogeneous group of diseases. The International Union of Immunological Societies Expert Committee categorizes PIDs into nine different categories: 1) combined immunodeficiencies, 2) combined immunodeficiencies with associated or syndromic features, 3) predominantly antibody deficiencies, 4) diseases of immune dysregulation, 5) congenital defects of phagocyte number, function, or both, 6) defects in intrinsic and innate immunity, 7) autoinflammatory disorders, 8) complement deficiencies and 9) phenocopies of PIDs. Despite a heterogeneous genetic basis, the core symptoms are often very similar and can complicate the diagnosis. In addition, many PIDs may be included in more than one category. Without knowing the specific mutation in the causative gene, treatment choice can be a complicated process. Also, type and site of and specific organisms causing the infections may help to classify the disease. In addition to immune-related symptoms, many PIDs have non-immune manifestations. The prevalence of individual PIDs have a wide range, but the combined prevalence of all primary immunodeficiencies is reported to be as high as 5-8:10,000. Some recently identified PIDs are extremely rare.

Primary ciliary dyskinesia (PCD) is a disorder characterized by chronic respiratory tract infections, situs abnormalities (situs ambiguous and situs inversus), and sometimes infertility due to abnormal sperm motility. The signs and symptoms of this condition are caused by abnormal cilia. Affected patients may have signs of PCD at birth or within the first few months of life; however, the symptoms and disease onset vary depending on the underlying genetic defect. Most full-term neonates have respiratory distress with tachypnea (infant acute respiratory distress syndrome). Typical findings in infants and children include daily rhinitis and daily year-round wet cough occurring soon after birth with associated recurrent or chronic infections of the lower airways. Patients with PCD, especially young children, may also experience recurrent ear infections (otitis media). The prevalence of PCD is difficult to determine. Among population isolates with a high rate of consanguinity, the incidence rate may be especially high. The total number of individuals with PCD in the United States is estimated to be 12,000-17,000. PCD has an estimated incidence of 1:15,000-1:30,000 live births; however, this is probably an underestimate. The Primary Ciliary Dyskinesia Panel includes testing for cystic fibrosis (CF), which is characterized by the production of sweat with a high salt content and mucus secretions with an abnormal viscosity. CF is caused by mutations in the CFTR gene. The disease is chronic and generally progressive, with onset usually occurring during early childhood.

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.