Masking selected sequence variation by incorporating mismatches into melting analysis probes

Journal ArticleHybridization probe melting analysis can be complicated by the presence of sequence variations (benign polymorphisms or other mutations) near the targeted mutation. We investigated the use of 'masking' probes to differentiate alleles with similar probe melting temperatures. Selected sequence variation was masked by incorporating deletions, unmatched nucleotides, or universal bases into hybridization probes. Such masking probes create a probe:target mismatch with all possible alleles at the selected polymorphic location. Any allele with additional variation at another site is identified by a lower probe melting temperature than alleles that vary only at the masked position. This technique was applied to RET and HPA6 mutation detection using unlabeled hybridization probes, a saturating dsDNA dye and high-resolution melting analysis

Masking techniques: masking selected sequence variation by incorporating mismatches into melting analysis probes

ReportHybridization probe melting analysis can be complicated by the presence of sequence variation (non-pathogenic polymorphisms or other mutations) near the targeted mutation. We investigated the use of 'masking' probes to differentiate alleles with similar probe melting temperatures. Materials and Methods: Selected sequence variation was masked by incorporating deletions, unmatched (non-complementary) nucleotides, or universal bases into hybridization probes. Such masking probes create a probe:target mismatch with all possible alleles at the selected polymorphic location. Any allele with additional variation at another site is identified by a lower probe melting temperature than alleles that vary only at the masked position. This technique was applied to RET proto-oncogene and HPA6 mutation detection using unlabeled hybridization probes, a saturating dsDNA dye, and high-resolution melting analysis

Germline Mutations in NFKB2 Implicate the Noncanonical NF-κB Pathway in the Pathogenesis of Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is a heterogeneous disorder characterized by antibody deficiency, poor humoral response to antigens, and recurrent infections. To investigate the molecular cause of CVID, we carried out exome sequence analysis of a family diagnosed with CVID and identified a heterozygous frameshift mutation, c.2564delA (p.Lys855Serfs∗7), in NFKB2 affecting the C terminus of NF-κB2 (also known as p100/p52 or p100/p49). Subsequent screening of NFKB2 in 33 unrelated CVID-affected individuals uncovered a second heterozygous nonsense mutation, c.2557C>T (p.Arg853∗), in one simplex case. Affected individuals in both families presented with an unusual combination of childhood-onset hypogammaglobulinemia with recurrent infections, autoimmune features, and adrenal insufficiency. NF-κB2 is the principal protein involved in the noncanonical NF-κB pathway, is evolutionarily conserved, and functions in peripheral lymphoid organ development, B cell development, and antibody production. In addition, Nfkb2 mouse models demonstrate a CVID-like phenotype with hypogammaglobulinemia and poor humoral response to antigens. Immunoblot analysis and immunofluorescence microscopy of transformed B cells from affected individuals show that the NFKB2 mutations affect phosphorylation and proteasomal processing of p100 and, ultimately, p52 nuclear translocation. These findings describe germline mutations in NFKB2 and establish the noncanonical NF-κB signaling pathway as a genetic etiology for this primary immunodeficiency syndrome

Rapid Diagnosis of MEN2B Using Unlabeled Probe Melting Analysis and the LightCycler 480 Instrument

Multiple endocrine neoplasia type 2B (MEN2B) is an autosomal dominant, inherited cancer syndrome. MEN2B patients have a high risk of developing medullary thyroid carcinoma, and prophylactic thyroidectomy is recommended by 6 months of age. Genetic testing can identify MEN2B patients before cancer progression. Two RET proto-oncogene mutations, in exon 15 at codon 883 (GCT>TTT) and in exon 16 at codon 918 (ATG>ACG), account for more than 98% of MEN2B cases. An assay using unlabeled probes and the LightCycler 480 instrument was developed to genotype these two common MEN2B RET mutations. Asymmetric polymerase chain reaction was used to increase ssDNA products followed by melting analysis of the unlabeled probe/ssDNA amplicon duplex. The available samples were either patient DNA of known RET genotype or artificial templates. Analysis of the codon 883 heterozygous mutation demonstrated a ΔTm of 5.70 ± 0.11°C, while the codon 918 heterozygous mutation generated a ΔTm of −5.72 ± 0.11°C. Samples with the targeted RET mutation genotypes were accurately detected and easily distinguishable from five other reported sequence changes using these probes. Thus, MEN2B diagnosis using unlabeled probes and the LightCycler 480 is a rapid, closed-tube method that is less time consuming and less expensive than sequencing. This assay demonstrates 100% specificity and sensitivity for the identification of RET mutations causative of MEN2B