Development of a genomic DNA reference material panel for Rett syndrome (MECP2-related disorders) genetic testing.

Rett syndrome is a dominant X-linked disorder caused by point mutations (approximately 80%) or by deletions or insertions (approximately 15% to 18%) in the MECP2 gene. It is most common in females but lethal in males, with a distinctly different phenotype. Rett syndrome patients have severe neurological and behavioral problems. Clinical genetic testing laboratories commonly use characterized genomic DNA reference materials to assure the quality of the testing process; however, none are commercially available for MECP2 genetic testing. The Centers for Disease Control and Prevention's Genetic Testing Reference Material Coordination Program, in collaboration with the genetic testing community and the Coriell Cell Repositories, established 27 new cell lines and characterized the MECP2 mutations in these and in 8 previously available cell lines. DNA samples from the 35 cell lines were tested by eight clinical genetic testing laboratories using DNA sequence analysis and methods to assess copy number (multiplex ligation-dependent probe amplification, semiquantitative PCR, or array-based comparative genomic hybridization). The eight common point mutations known to cause approximately 60% of Rett syndrome cases were identified, as were other MECP2 variants, including deletions, duplications, and frame shift and splice-site mutations. Two of the 35 samples were from males with MECP2 duplications. These MECP2 and other characterized genomic DNA samples are publicly available from the NIGMS Repository at the Coriell Cell Repositories.

Truncating CLCN1 mutations in myotonia congenita: variable patterns of inheritance.

INTRODUCTION: Myotonia congenita due to protein truncating CLCN1 mutations is associated with variable patterns of inheritance. METHODS: Three family kindreds are described, all of whom possess protein truncating mutations (Y33X, fs503X, R894X). One lineage also has coexistent R894X, A313T, and A320V mutations. RESULTS: The Y33X mutation kinship has autosomal recessive inheritance and a severe phenotype when homozygous. The fs503X family has autosomal dominant inheritance and a moderate-to-severe phenotype. The A313T mutation kindred also has autosomal dominant inheritance but expresses a mild phenotype, except for the more severely affected compound heterozygotes. CONCLUSIONS: Early truncating mutations precluding dimerization are expected to be autosomal recessive and express a severe phenotype, while later mutations may be variable. The pedigrees presented here demonstrate that intrafamilial phenotypic variability may result from a dosage effect of an additional mutation, not necessarily variable expressivity. Mutations that have unexpected patterns of inheritance may represent allelic variability.

Development of a genomic DNA reference material panel for myotonic dystrophy type 1 (DM1) genetic testing.

Myotonic dystrophy type 1 (DM1) is caused by expansion of a CTG triplet repeat in the 3' untranslated region of the DMPK gene that encodes a serine-threonine kinase. Patients with larger repeats tend to have a more severe phenotype. Clinical laboratories require reference and quality control materials for DM1 diagnostic and carrier genetic testing. Well-characterized reference materials are not available. To address this need, the Centers for Disease Control and Prevention-based Genetic Testing Reference Material Coordination Program, in collaboration with members of the genetic testing community, the National Registry of Myotonic Dystrophy and Facioscapulohumeral Muscular Dystrophy Patients and Family Members, and the Coriell Cell Repositories, has established and characterized cell lines from patients with DM1 to create a reference material panel. The CTG repeats in genomic DNA samples from 10 DM1 cell lines were characterized in three clinical genetic testing laboratories using PCR and Southern blot analysis. DMPK alleles in the samples cover four of five DM1 clinical categories: normal (5 to 34 repeats), mild (50 to 100 repeats), classical (101 to 1000 repeats), and congenital (>1000 repeats). We did not identify or establish Coriell cell lines in the premutation range (35 to 49 repeats). These samples are publicly available for quality control, proficiency testing, test development, and research and should help improve the accuracy of DM1 testing.

Developmental trajectories in syndromes with intellectual disability, with a focus on Wolf-Hirschhorn and its cognitive-behavioral profile.

Few studies exist of developmental trajectories in children with intellectual disability, and none for those with subtelomeric deletions. We compared developmental trajectories of children with Wolf-Hirschhorn syndrome to other genetic disorders. We recruited 106 children diagnosed with fragile X, Williams-Beuren syndrome, or Wolf-Hirschhorn syndrome, assessing their intellectual and adaptive behavior abilities. We retested 61 children 2 years later. We compared Time 1 and Time 2 difference scores related to genetic disorder, age, initial IQ, or adaptive behavior composite. Results show genetic disorder and initial IQ score were significant factors for IQ differences, but only genetic disorder affected adaptive behavior differences. Results suggest different gene-brain-behavior pathways likely exist for these genetic disorders. Different developmental trajectories will influence the type and intensity of intervention implemented by caregivers.

Quality assurance for Duchenne and Becker muscular dystrophy genetic testing: development of a genomic DNA reference material panel.

Duchenne and Becker muscular dystrophies (DMD/BMD) are allelic X-linked recessive disorders that affect approximately 1 in 3500 and 1 in 20,000 male individuals, respectively. Approximately 65% of patients with DMD have deletions, 7% to 10% have duplications, and 25% to 30% have point mutations in one or more of the 79 exons of the dystrophin gene. Most clinical genetics laboratories test for deletions, and some use technologies that can detect smaller mutations and duplications. Reference and quality control materials for DMD/BMD diagnostic and carrier genetic testing are not commercially available. To help address this need, the Centers for Disease Control and Prevention-based Genetic Testing Reference Material Coordination Program, in collaboration with members of the genetic testing and the DMD/BMD patient communities and the Coriell Cell Repositories, have characterized new and existing cell lines to create a comprehensive DMD/BMD reference material panel. Samples from 31 Coriell DMD cell lines from male probands and female carriers were analyzed using the Affymetrix SNP Array 6.0 and Multiplex Ligation-Dependent Probe Amplification (MRC-Holland BV, Amsterdam, the Netherlands), a multiplex PCR assay, and DNA sequence analysis. Identified were 16 cell lines with deletions, 9 with duplications, and 4 with point mutations distributed throughout the dystrophin gene. There were no discordant results within assay limitations. These samples are publicly available from Coriell Institute for Medical Research (Camden, NJ) and can be used for quality assurance, proficiency testing, test development, and research, and should help improve the accuracy of DMD testing.

The course of cognitive-behavioral development in children with the FMR1 mutation, Williams-Beuren syndrome, and neurofibromatosis type 1: The effect of gender.

The course of cognitive-behavioral development in children with intellectual disabilities produced by genetic disorders has only recently begun to be examined systematically. Unfortunately, these studies are few in number. Previously, we examined cognitive-behavioral development in children with the fragile X (FMR1) mutation and found longitudinal decreases in both IQ and adaptive behavior (DQ) scores in most males and females with the full mutation. In this study, we examine longitudinal changes in IQ and DQ in children with neurofibromatosis type 1 (NF1) and Williams-Beuren Syndrome (WBS) by examining differences in composite IQ and DQ scores between the first test (T1) and retest (T2), and compare their developmental trajectory to children with the FMR1 mutation. Sixty-five children with the FMR1 mutation, or NF1, or WBS, ages 4-16 years, were retested two years after initial testing with the Stanford-Binet 4th Edition (SBFE) and the Vineland Adaptive Behavior Scale (VABS). In addition to significant longitudinal declines in IQ and DQ noted previously in children with the FMR1 mutation, we found significant decreases in IQ in males compared to females in the remainder of our sample. We also observed statistically significant decreases in DQ scores among children the FMR1 mutation, as noted previously, but not among children with NF1 or WBS. Moreover, significant declines were found only among males with the FMR1 mutation. Unlike declines in IQ scores, decreases in DQ were not significantly different between males and females.

Development of genomic reference materials for cystic fibrosis genetic testing.

The number of different laboratories that perform genetic testing for cystic fibrosis is increasing. However, there are a limited number of quality control and other reference materials available, none of which cover all of the alleles included in commercially available reagents or platforms. The alleles in many publicly available cell lines that could serve as reference materials have neither been confirmed nor characterized. The Centers for Disease Control and Prevention-based Genetic Testing Reference Material Coordination Program, in collaboration with members of the genetic testing community as well as Coriell Cell Repositories, have characterized an extended panel of publicly available genomic DNA samples that could serve as reference materials for cystic fibrosis testing. Six cell lines [containing the following mutations: E60X (c.178G>T), 444delA (c.312delA), G178R (c.532G>C), 1812-1G>A (c.1680-1G>A), P574H (c.1721C>A), Y1092X (c.3277C>A), and M1101K (c.3302T>A)] were selected from those existing at Coriell, and seven [containing the following mutations: R75X (c.223C>T), R347H (c.1040G>A), 3876delA (c.3744delA), S549R (c.1646A>C), S549N (c.1647G>A), 3905insT (c.3773_3774insT), and I507V (c.1519A>G)] were created. The alleles in these materials were confirmed by testing in six different volunteer laboratories. These genomic DNA reference materials will be useful for quality assurance, proficiency testing, test development, and research and should help to assure the accuracy of cystic fibrosis genetic testing in the future. The reference materials described in this study are all currently available from Coriell Cell Repositories.

Recessive CLCN1 mutation presenting as Thomsen disease.

This case report describes a young man referred for electrodiagnostic evaluation for hand stiffness and intermittent numbness. His needle electromyography revealed diffusely increased insertional and spontaneous motor activity in the form of myotonic discharges. Given the finding of symptomatic myotonia also in his mother, Thomsen myotonia was suspected. Investigations not only confirmed Thomsen myotonia, but also led to the identification of a previously reported heterozygous Becker mutation in both the proband and his mother.

Extraocular muscle hypertrophy in myotonia congenita.

Myotonia congenita (MC) is a rare disorder of skeletal muscle caused by mutations in the CLCN1 gene,(1,2) which encodes the chloride ion channel found in the t-tubule of skeletal muscle. MC is characterized by impaired relaxation of voluntary muscle after sudden contraction that diminishes with muscle activity, known as the "warm-up effect." Individuals with MC can develop muscular hypertrophy despite little physical activity. Esotropia and reduced saccadic velocities have been reported in the dominant form of MC. We report two cases in which orbital magnetic resonance imaging (MRI) imaging showed extraocular muscle hypertrophy.

Studies of age-correlated features of cognitive-behavioral development in children and adolescents with genetic disorders.

Studies of age-related features of cognitive-behavioral deficits produced by genetic mutations permit us to draw inferences about how brain development may be related cognitive ability as the child ages. Except for Down syndrome (DS) and the fragile X mutation (FRAXA), little is known about the longitudinal changes in cognitive-behavioral development in individuals with genetic abnormalities producing learning disabilities (LD) or mental retardation (MR). The purpose of this prospective study was to compare and contrast age related to cognitive abilities, adaptive and maladaptive behaviors in children and adolescents in the same age range, diagnosed with one of three genetic disorders: the FRAXA mutation, Neurofibromatosis type 1 (NF1) or Williams-Beuren syndrome (WBS). We also sought to examine whether cognitive-behavioral abilities associated with these three genetic disorders were related systematically to age. We examined 108 children, ages 4-15 years, with FRAXA, WBS, or NF1. Results show that there is a significant negative correlation between age and IQ, and between age and adaptive behavior (DQ) scores, in children with FRAXA and WBS, but not in children with NF1. All three groups of children have unusually high proportions of maladaptive behavior, ranging from 1/6 children with NF1 to 2/3 children with FRAXA. Cognitive and adaptive behavior profiles of children with FRAXA and WBS were also surprisingly similar. Our findings suggest the need for examining longitudinal developmental cognitive-behavioral changes in children and adolescents with all genetic disorders that produce LD or MR.