Christoffer Jonsrud

Current clinical criteria for Lynch syndrome are not sensitive enough to identify MSH6 mutation carriers

Background Reported prevalence, penetrance and expression of deleterious mutations in the mismatch repair (MMR) genes, MLH1, MSH2, MSH6 and PMS2, may reflect differences in the clinical criteria used to select families for DNA testing. The authors have previously reported that clinical criteria are not sensitive enough to identify MMR mutation carriers among incident colorectal cancer cases. Objective To describe the sensitivity of the criteria when applied to families with a demonstrated MMR mutation. Methods Families with an aggregation of colorectal cancers were examined for deleterious MMR mutations according to the Mallorca guidelines. All families with a detected MMR mutation as of November 2009 were reclassified according to the Amsterdam and Bethesda criteria. Results Sixty-nine different DNA variants were identified in a total of 129 families. The original Amsterdam clinical criteria were met by 38%, 12%, 78% and 25% of families with mutations in MSH2, MSH6, MLH1 and PMS2, respectively. Corresponding numbers for the revised Amsterdam criteria were 62%, 48%, 87% and 38%. Similarly, each of the four clinical Bethesda criteria had low sensitivity for identifying MSH6 or PMS2 mutations. Conclusion Amsterdam criteria and each of the Bethesda criteria were inadequate for identifying MSH6 mutation-carrying kindreds. MSH6 mutations may be more common than currently assumed, and the penetrance/expression of MSH6 mutations, as derived from families meeting current clinical criteria, may be misleading. To increase detection rate of MMR mutation carriers, all cancers in the Lynch syndrome tumour spectrum should be subjected to immunohistochemical analysis and/or analysis for microsatellite instability.

A novel late-onset axial myopathy associated with mutations in the skeletal muscle ryanodine receptor (RYR1) gene

Mutations in the skeletal muscle ryanodine receptor (RYR1) gene are a common cause of inherited neuromuscular disorders and have been associated with a wide clinical spectrum, ranging from various congenital myopathies to the malignant hyperthermia susceptibility (MHS) trait without any associated weakness. RYR1-related myopathies are usually of early-childhood onset. Here we present 11 patients from 8 families with a late-onset axial myopathy associated with RYR1 variants. Patients presented between the third and seventh decade of life to neuromuscular centres in Norway, the Netherlands and the United Kingdom with predominant axial muscle involvement, comprising variable degrees of lumbar hyperlordosis, scapular winging and/or camptocormia. Marked myalgia was commonly associated. Serum creatine kinase levels were normal or moderately elevated. Muscle imaging showed consistent involvement of the lower paravertebral muscles and the posterior thigh. Muscle biopsy findings were often discrete, featuring variability in fibre size, increased internal nuclei and unevenness of oxidative enzyme staining, but only rarely overt cores. RYR1 sequencing revealed heterozygous missense variants, either previously associated with the MHS trait or localizing to known MHS mutational hotspots. These findings indicate that MHS-related RYR1 mutations may present later in life with prominent axial weakness but not always typical histopathological features. We propose a combined effect of RyR1 dysfunction, aging and particular vulnerability of axial muscle groups as a possible pathogenic mechanism. RYR1 is a candidate for cases with “idiopathic” camptocormia or bent spine syndrome (BSS).

Prevalence, mutation spectrum and phenotypic variability in Norwegian patients with Limb Girdle Muscular Dystrophy 2I

Mutations in the FKRP (Fukutin Related Protein) gene produce a range of phenotypes including Limb Girdle Muscular Dystrophy Type 2I (LGMD2I). In order to investigate the prevalence, the mutation spectrum and possible genotype-phenotype correlation, we studied a cohort of Norwegian patients with LGMD2I, ascertained in a 4-year period. In this retrospective study of genetically tested patients, we identified 88 patients from 69 families, who were either homozygous or compound heterozygous for FKRP mutations. This gives a minimum prevalence of 1/54,000 and a corresponding carrier frequency of 1/116 in the Norwegian population. Seven different FKRP mutations, including three novel changes, were detected. Seventy-six patients were homozygous for the common c.826C>A mutation. These patients had later disease onset than patients who were compound heterozygous - 14.0 vs. 6.1 years. We detected substantial variability in disease severity among homozygous patients.

Causes of hearing impairment in the Norwegian paediatric cochlear implant program.

Abstract Severe to profound hearing impairment (HI) is estimated to affect around 1/2000 young children. Advances in genetics have made it possible to identify several genes related to HI. This information can cast light upon prognostic factors regarding the outcome in cochlear implantation, and provide information both for scientific and genetic counselling purposes. From 1992 to 2005, 273 children from 254 families (probands) were offered cochlear implants in Norway. An evaluation of the causes of HI, especially regarding the genes GJB2, GJB6, SLC26A4, KCNQ1, KCNE1, and the mutation A1555G in mitochondrial DNA was performed in 85% of the families. The number of probands with unknown cause of HI was thus reduced from 120 to 68 (43% reduction). Ninety-eight (46%) of the probands had an identified genetic etiology of their HI. A relatively high prevalence of Jervell and Lange-Nielsen syndrome was found. The main causes of severe and profound HI were similar to those found in other European countries. GJB2 mutations are a common cause of prelingual HI in Norwegian cochlear implanted children. Sumario Se estima que la hipoacusia (HI) severa a profunda afecta alrededor de 1/2000 niños pequeños. Los avances en la genética han hecho posible la identificación de varios genes relacionados con HI. Esta información puede proporcionar luz en los factores pronóstico relacionados con el resultado de los implantes cocleares, y dar información tanto para fines científicos como para asesoramiento genético. De 1992 a 2005, a 273 niños de 254 familias (propósitos) se les ofreció un implante coclear en Noruega. Una evaluación de las causas de la HI, especialmente de los genes GJB2, GJB6, SLC26A4, KCNQ1, KCNE1 y la mutación A1555G del DNA mitocondrial se realizó en 85% de las familias. El número de propósitos con causa desconocida de HI se redujo de 120 a 68 (reducción del 43%). Noventa y ocho (46%) de los sujetos tuvieron una causa genética identificada. Se encontró una prevalencia relativamente alta del Síndrome de Jervell and Lange Nielsen. Las principales causas de la HI severa a profunda fueron similares a las encontradas en los países Europeos. Las mutaciones de GJB2 son una causa común de hipoacusia pre-lingüística en niños noruegos con implante coclear.

A heterozygous 21-bp deletion in CAPN3 causes dominantly inherited limb girdle muscular dystrophy

Limb girdle muscular dystrophy type 2A is the most common limb girdle muscular dystrophy form worldwide. Although strict recessive inheritance is assumed, patients carrying a single mutation in the calpain 3 gene (CAPN3) are reported. Such findings are commonly attributed to incomplete mutation screening. In this investigation, we report 37 individuals (age range: 21-85 years, 21 females and 16 males) from 10 families in whom only one mutation in CAPN3 could be identified; a 21-bp, in-frame deletion (c.643_663del21). This mutation co-segregated with evidence of muscle disease and autosomal dominant transmission in several generations. Evidence of muscle disease was indicated by muscle pain, muscle weakness and wasting, significant fat replacement of muscles on imaging, myopathic changes on muscle biopsy and loss of calpain 3 protein on western blotting. Thirty-one of 34 patients had elevated creatine kinase or myoglobin. Muscle weakness was generally milder than observed in limb girdle muscular dystrophy type 2A, but affected the same muscle groups (proximal leg, lumbar paraspinal and medial gastrocnemius muscles). In some cases, the weakness was severely disabling. The 21-bp deletion did not affect mRNA maturation. Calpain 3 expression in muscle, assessed by western blot, was below 15% of normal levels in the nine mutation carriers in whom this could be tested. Haplotype analysis in four families from three different countries suggests that the 21-bp deletion is a founder mutation. This study provides strong evidence that heterozygosity for the c.643_663del21 deletion in CAPN3 results in a dominantly inherited muscle disease. The normal expression of mutated mRNA and the severe loss of calpain 3 on western blotting, suggest a dominant negative effect with a loss-of-function mechanism affecting the calpain 3 homodimer. This renders patients deficient in calpain 3 as in limb girdle muscular dystrophy type 2A, albeit in a milder form in most cases. Based on findings in 10 families, our study indicates that a dominantly inherited pattern of calpainopathy exists, and should be considered in the diagnostic work-up and genetic counselling of patients with calpainopathy and single-allele aberrations in CAPN3.

High penetrances of BRCA1 and BRCA2 mutations confirmed in a prospective series

Penetrances of BRCA1 and BRCA2 mutations have been derived from retrospective studies, implying the possibility of ascertainment biases to influence the results.We have followed women at risk for breast and/or ovarian cancer for two decades, and report the prospectively observed age-related annual incidence rates to contract breast or ovarian cancer for women with deleterious BRCA1 or BRCA2 mutations based on 4830 observation years. Patients were grouped according to mutation, age and having/not having had previous cancer.In women not having had previous cancer and aged 40-59 years, the annual incidence rate to contract breast or ovarian cancer in those having the most frequent BRCA1 founder mutations was 4.0%, for women in this age group and with less frequent BRCA1 mutations annual incidence rate was 5.9%, and for women with BRCA2 mutations 3.5%.The observed figures may be used for genetic counseling of healthy mutation carriers in the respective age groups. The results may indicate that less frequent BRCA1 mutations have higher penetrances than BRCA1 founder mutations.

G.P.277

To investigate if there is a correlation between clinical expression (duration of disease, age, walking function) and morphological alterations in affected muscle (structural changes, immunohistochemical and the level of alpha-DG glycosylation) among 25 patients with Limb Girdle Muscular Dystrophy type 2I (LGMD2I) all with the common C.826C>A mutation ). Muscle biopsies were obtained from 25 patients. Quantitative evaluation of morphological alterations in muscle sections, and immunohistochemistry (IHC) with antibodies directed against the alpha-dystroglycan glycan epitope, was performed by light microscopy. A semi-quantitative assessment of changes was recorded, point-graded and summarized as morphological sum-score for each biopsy.. Western blot (WB) analysis on muscle biopsy homogenates were carried with antibodies directed towards the core alpha-DG as well as the alpha-DG-glycan epitope. Laminin overlay was included. Muscle biopsies from 25 patients with LGMD2I presented large variation in morphological features. All biopsies presented reduced molecular weight of alpha-DG as detected with alpha-DG core antibody on WB analysis. Immunohistochemistry and WB analysis directed towards the alpha-DG-glycan epitope, as well as laminin overlay, demonstrated large variation in signal intensity among the LGMD2I patients. Results from IHC and WB/laminin overlay correlated poorly. There was no obvious correlation between ages at onset or duration of disease at biopsy versus the level of alpha-DG glycosylation. Likewise, there was no apparent association between severities of disease and the sum-scores of structural changes in the muscle biopsies. The clinical and morphological variability seen among LGMD2I patients with identical FKRP genotype must therefore be explained by other genetic or environmental mechanisms.

P.8.1 Muscle biopsy findings in Limb Girdle muscle Dystrophy 2I (LGMD2I)

To assess potential correlation of severity of Limb Girdle Muscular Dystrophy type 2I (LGMD2I) with morphological, immunohistochemical and immunoblot alterations, in muscle biopsies from 27 patients with (LGMD2I). Mutations in the FKRP (Fukutin Related Protein) gene produce a range of clinical phenotypes including Limb Girdle Muscular Dystrophy Type 2I (LGMD2I), which belong to the mild end of the clinical spectrum. Seven different FKRP mutations have been detected among Norwegian LGMD2I patients of whom the majority were homozygous for the common c.826C>A mutation, and presented with a milder phenotype. Muscle biopsies were obtained from 27 patients. Quantitative evaluation of morphological alterations in muscle cross- sections, and immunohistochemistry (IHC) with antibodies directed against the alpha-dystroglycan epitope, was performed by light microscopy. A semi-quantitative assessment of changes was recorded, point-graded and summarized as morphological sum-score for each biopsy. The following myopathic changes were graded in the scoring system: fibrosis, regeneration, atrophy, centralized nuclei, necrosis, and inflammation. Western blot (WB) analysis on muscle biopsy homogenates were carried with antibodies directed towards the core alpha-DG as well as the alpha-DG epitope. Muscle biopsies from 27 patients with LGMD2I presented large variation in morphological features (Table 1).