Detection of Common Disease-Causing Mutations in Mitochondrial DNA (Mitochondrial Encephalomyopathy, Lactic Acidosis with Stroke-Like Episodes MTTL1 3243 A>G and Myoclonic Epilepsy Associated with Ragged-Red Fibers MTTK 8344A>G) by Real-Time Polymerase Chain Reaction

The 3243A>G mutation in the MTTL1 (tRNA(Leu)) gene and the 8344A>G mutation in the MTTK (tRNA(Lys)) gene are the most common mutations found in mitochondrial encephalomyopathy, lactic acidosis with stroke-like episodes and myoclonic epilepsy associated with ragged-red fibers, respectively. These mitochondrial DNA mutations are usually detected by conventional polymerase chain reaction followed by restriction enzyme digestion and gel electrophoresis. We developed a LightCycler real-time polymerase chain reaction assay to detect these two mutations based on fluorescence resonance energy transfer technology and melting curve analysis. Primers and fluorescence-labeled hybridization probes were designed so that the sensor probe spans the mutation site. The observed melting temperatures differed in the mutant and wild-type DNA by 9°C for the MTTL1 gene and 6°C for the MTTK gene. This method correctly identified all 10 samples that were 3243A>G mutation-positive, all 4 samples that were 8344A>G mutation-positive, and all 30 samples that were negative for both mutations, as previously identified by traditional gel-based methods. This LightCycler assay is a rapid and reliable technique for molecular diagnosis of these mitochondrial gene mutations

Diagnosis of Human Congenital Cytomegalovirus Infection by Amplification of Viral DNA from Dried Blood Spots on Perinatal Cards

Congenital human cytomegalovirus (HCMV) infection affects 1% of children and is the most common infectious cause of sensorineural hearing loss. Due to the difficulty of diagnosing deafness and other neurological disorders in infants, affected individuals may not be recognized until much later when active infection has resolved and culture is no longer informative. To overcome this problem, congenital HCMV infection was diagnosed retrospectively by testing residual blood samples collected from newborns and dried on perinatal cards as part of the North Carolina Newborn Screening Program. We modified the Qiagen method for purifying DNA from dried blood spots to increase the sample size and recovery of the lysate. A multiplex, real-time TaqMan polymerase chain reaction assay on an ABI 7900 instrument measured a highly conserved segment of the HCMV polymerase gene and the APOB human control gene. HCMV DNA was detected in blood dried on perinatal cards from all seven infants with culture-proven congenital infection, and all 24 negative control cases lacked detectable HCMV DNA. Our findings suggest that it is possible to diagnose congenital HCMV infection using dried blood collected up to 20 months earlier. Further studies are warranted on patients with hearing loss or other neurological deficits to determine the percentage that is attributable to congenital HCMV infection

Characterization of 107 Genomic DNA Reference Materials for CYP2D6, CYP2C19, CYP2C9, VKORC1, and UGT1A1: A GeT-RM and Association for Molecular Pathology Collaborative Project

Pharmacogenetic testing is becoming more common; however, very few quality control and other reference materials that cover alleles commonly included in such assays are currently available. To address these needs, the Centers for Disease Control and Prevention's Genetic Testing Reference Material Coordination Program, in collaboration with members of the pharmacogenetic testing community and the Coriell Cell Repositories, have characterized a panel of 107 genomic DNA reference materials for five loci (CYP2D6, CYP2C19, CYP2C9, VKORC1, and UGT1A1) that are commonly included in pharmacogenetic testing panels and proficiency testing surveys. Genomic DNA from publicly available cell lines was sent to volunteer laboratories for genotyping. Each sample was tested in three to six laboratories using a variety of commercially available or laboratory-developed platforms. The results were consistent among laboratories, with differences in allele assignments largely related to the manufacturer's assay design and variable nomenclature, especially for CYP2D6. The alleles included in the assay platforms varied, but most were identified in the set of 107 DNA samples. Nine additional pharmacogenetic loci (CYP4F2, EPHX1, ABCB1, HLAB, KIF6, CYP3A4, CYP3A5, TPMT, and DPD) were also tested. These samples are publicly available from Coriell and will be useful for quality assurance, proficiency testing, test development, and research