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Biomedical subjects

N Dahl

Publications and source records attributed to N Dahl.

At least 37 records · Page 2Linked to original sources
PubMed1999

Autosomal dominant myofibrillar myopathy with arrhythmogenic right ventricular cardiomyopathy linked to chromosome 10q.

Twenty-one members of a Swedish family suffering from myopathy and cardiomyopathy underwent neurological and cardiological investigations. Medical charts of 2 affected deceased patients were reviewed. Twelve patients had myopathy. The distribution of weakness was axial in mildly affected, axial and predominantly distal in moderately affected, and generalized in severely affected patients. The electromyogram showed signs of myopathy in 10 patients. Muscle biopsy specimens showed myopathic changes, rimmed vacuoles, and accumulation of desmin, dystrophin, and other proteins. Electron microscopy revealed granulofilamentous changes and disorganization of myofibrils. Several patients had episodes of chest pain or palpitations. Three men had arrhythmogenic right ventribular cardiomyopathy. Nonsustained ventribular tachycardia, atrial flutter, and dilatation of the ventricles mainly affecting the right ventricle were documented. Two of them had a pacemaker implanted because of atrioventricular block and sick sinus syndrome. Inheritance is autosomal dominant with variable onset and severity of skeletal muscle and cardiac involvement. Linkage analysis of candidate chromosomal regions showed a maximum 2-point LOD score of 2.76 for marker locus D10S1752 on chromosome 10q. A multipoint peak LOD score of 3.06 between markers D10S605 and D10S215 suggests linkage to chromosome 10q22.3, and this region may harbor a genetic defect for myofibrillar myopathy with arrhythmogenic right ventricular cardiomyopahty.

Adult↗
PubMed1999

Alpha-tectorin involvement in hearing disabilities: one gene--two phenotypes.

The human alpha-tectorin (TECTA) gene has recently been cloned and proposed to be involved in autosomal dominant non-syndromic hearing impairment (NSHI) in two families linked to the DFNA12 locus. We have studied a Swedish pedigree with autosomal dominant NSHI with possible digenic inheritance of the disease, involving locus DFNA12 in chromosome 11 and locus DFNA2 in chromosome 1. Mutation analysis of the TECTA gene in this family has identified eight nucleotide substitutions indicating that TECTA is highly polymorphic. One of the changes results in a cysteine to serine (C 1057 S) mutation, in the zonadhesin domain of TECTA; this segregates with the disease haplotype on chromosome 11 and is not present in a control population. The mutation results in the replacement of a cysteine in one of the repeats of the zonadhesin/Von Willebrand domain of the protein and might cause a change in the crosslinking of the polypeptide. These findings add support to the involvement of TECTA in hearing disabilities. However, the three families carrying different TECTA mutations also show phenotypic differences: the hearing loss ranges from prelingual to progressive with late onset. The explanation for the different phenotypes and some clues regarding the functions of TECTA may lie in the localization of the mutations in the different modules of the protein. Another possibility is that the phenotype in the Swedish family is the result of two defective genes.

Amino Acid Sequence↗
PubMed1999

Truncating ribosomal protein S19 mutations and variable clinical expression in Diamond-Blackfan anemia.

Diamond-Blackfan anemia (DBA) is a rare constitutional erythroblastopenia characterized by a specific defect in erythroid differentiation. Recently, mutations in the gene encoding ribosomal protein (RP) S19 were found in a subset of patients with the disease. To characterize further RPS19 mutations and to investigate genotype-phenotype relationships, we screened this gene for mutations in patients with DBA by direct sequencing and Southern-blot analysis. Four novel mutations were identified. A G120A nonsense mutation resulting in a stop at codon 33, a C302T nonsense mutation introducing a premature stop at codon 84, and a 327delG which results in a frame shift at codon 103. A fourth and more complex mutation (TT157-158AA, 160insCT) resulting in a Leu45Gln and a frame shift from codon 47 was found in three affected family members with variable phenotypes. The different clinical expression for identical mutations suggest the presence of other modulating factors for the disease. The mutations presented here further support the role of RPS19 in erythropoietic differentiation and proliferation.

Adult↗
PubMed1999

A microdeletion syndrome due to a 3-Mb deletion on 19q13.2--Diamond-Blackfan anemia associated with macrocephaly, hypotonia, and psychomotor retardation.

We report on a boy with congenital pure red blood cell aplasia [Diamond Blackfan anemia (DBA)] and severe congenital hypotonia, macrocephaly, hypertelorism, a broad and tall forehead, medial epicanthus, and facial hypotonia with mouth-breathing and drooling, an affable and out-going personality, and a general psychomotor retardation. These features show similarity to the phenotype of the X-linked FG syndrome. DBA was diagnosed at the age of 4 months, and the boy underwent treatment with transfusion and with prednisolone. He had a normal 46, XY karyotype, but fluorescence in situ hybridization (FISH) analysis to metaphase chromosomes revealed a 3-Mb deletion on 19q13.2. This chromosomal region has previously been linked to the DBA phenotype and one 19q13 microdeletion has been identified in a patient with DBA. This deletion coincides with the deletion reported here. We suggest that the complex phenotype of our patient, including both DBA and the associated features, represent a microdeletion syndrome.

Chromosome Deletion↗
PubMed1999

The gene encoding ribosomal protein S19 is mutated in Diamond-Blackfan anaemia.

Diamond-Blackfan anaemia (DBA) is a constitutional erythroblastopenia characterized by absent or decreased erythroid precursors. The disease, previously mapped to human chromosome 19q13, is frequently associated with a variety of malformations. To identify the gene involved in DBA, we cloned the chromosome 19q13 breakpoint in a patient with a reciprocal X;19 chromosome translocation. The breakpoint occurred in the gene encoding ribosomal protein S19. Furthermore, we identified mutations in RPS19 in 10 of 40 unrelated DBA patients, including nonsense, frameshift, splice site and missense mutations, as well as two intragenic deletions. These mutations are associated with clinical features that suggest a function for RPS19 in erythropoiesis and embryogenesis.

Amino Acid Sequence↗
PubMed1999

Deletion including the oligophrenin-1 gene associated with enlarged cerebral ventricles, cerebellar hypoplasia, seizures and ataxia.

Non-specific X-linked mental retardation is a heterogeneous group of disorders with an incidence of approximately 1 in 500 males. A recently identified gene in Xq12, encoding a Rho-GTPase-activating protein, was found to be mutated in individuals with mental retardation. We describe here two sisters with a 46,XY karyotype and a microdeletion of the oligophrenin-1 gene and 1.1 Mb of flanking DNA. We have characterised the molecular interval defining this microdeletion syndrome with the fibre-FISH technique. A visual physical map of 1.2 Mb was constructed which spans the oligophrenin-1 gene and the androgen receptor gene. The analysis of the patients revealed a deletion which extended from the 5' end of the AR gene to a region approximately 80 kb proximal to the EPLG2 gene. The clinical manifestations of the two sisters include psychomotor retardation, seizures, ataxia, hypotonia and complete androgen insensitivity. Cranial MRI scans show enlargement of the cerebral ventricles and cerebellar hypoplasia. Our findings give further support for the involvement of the oligophrenin-1 gene in specific morphological abnormalities of the brain which is of importance in the investigation of male patients presenting with mental retardation. In combination with our results from physical mapping we suggest that a region around the oligophrenin-1 locus is relatively bereft of vital genes.

Ataxia↗
PubMed1999

Diamond-Blackfan anaemia in the Italian population.

Diamond-Blackfan anaemia (DBA) is a congenital disease characterized by defective erythroid progenitor maturation: 30% of patients have congenital malformations. The link between these malformations and defective erythropoiesis is unclear: a defect in a molecule acting both on embryo development and haemopoiesis has been proposed. Inheritance is autosomal dominant in most familial cases, but recessive families have also been reported. Many cases are sporadic. A DBA locus has been mapped on chromosome 19q13.2 (Gustavsson et al, 1997), but several families unlinked to this locus have also been reported (Gustavsson et al, 1998). This paper presents clinical, epidemiological and molecular data for DBA in the Italian population. Segregation analysis of 19q markers in patients with DBA showed exclusion of this locus in 5/12 families with inherited DBA. There was evidently locus heterogeneity for DBA in this population. A new microdeletion was identified in one patient. Other families, in which DBA segregates concordantly with the 19q critical region, suggest incomplete penetrance and expressivity of the DBA gene.

Child↗
PubMed1999

The 2588G-->C mutation in the ABCR gene is a mild frequent founder mutation in the Western European population and allows the classification of ABCR mutations in patients with Stargardt disease.

In 40 western European patients with Stargardt disease (STGD), we found 19 novel mutations in the retina-specific ATP-binding cassette transporter (ABCR) gene, illustrating STGD's high allelic heterogeneity. One mutation, 2588G-->C, identified in 15 (37.5%) patients, shows linkage disequilibrium with a rare polymorphism (2828G-->A) in exon 19, suggesting a founder effect. The guanine at position 2588 is part of the 3' splice site of exon 17. Analysis of the lymphoblastoid cell mRNA of two STGD patients with the 2588G-->C mutation shows that the resulting mutant ABCR proteins either lack Gly863 or contain the missense mutation Gly863Ala. We hypothesize that the 2588G-->C alteration is a mild mutation that causes STGD only in combination with a severe ABCR mutation. This is supported in that the accompanying ABCR mutations in at least five of eight STGD patients are null (severe) and that a combination of two mild mutations has not been observed among 68 STGD patients. The 2588G-->C mutation is present in 1 of every 35 western Europeans, a rate higher than that of the most frequent severe autosomal recessive mutation, the cystic fibrosis conductance regulator gene mutation DeltaPhe508. Given an STGD incidence of 1/10,000, homozygosity for the 2588G-->C mutation or compound heterozygosity for this and other mild ABCR mutations probably does not result in an STGD phenotype.

ATP-Binding Cassette Transporters↗
PubMed1998

High adenosine deaminase level among healthy probands of Diamond Blackfan anemia (DBA) cosegregates with the DBA gene region on chromosome 19q13. The DBA Working Group of Société d'Immunologie Pédiatrique (SHIP).

Phenotypic characterization of Diamond Blackfan Anemia (DBA) patients and their relatives was performed in 54 families. Complete blood count, fetal hemoglobin level, erythrocyte i antigen expression, and erythrocyte adenosine deaminase (eADA) activities were quantitated in patients and relatives. eADA was elevated in 28 of 34 transfusion-independent DBA patients, whereas persistence of erythrocyte i antigen was noticed in only 10 of 20 DBA patients. High eADA activities were also found in 14 of 149 healthy family members, allowing us to identify an isolated high eADA phenotype in these families. In contrast, increase in erythrocyte i antigen expression, elevated fetal hemoglobin levels, and macrocytosis were much less frequently noted in nonaffected members of the DBA families studied. Importantly, isolated high eADA phenotype was found to be significantly associated with genetic markers on chromosome 19 that segregate with the DBA phenotype. Isolated high eADA phenotype thus seems to reflect a silent phenotype of DBA in affected families. These findings suggest that elevated eADA activity in unaffected individuals needs to be taken into account during genetic assessment of DBA families and could be used for accurate assessment of mode of inheritance.

Adenosine Deaminase↗
PubMed1998

Stargardt disease: linkage to the ABCR gene region on 1p21-p22 in Scandinavian families.

UNLABELLED: Stargardt disease (STGD) or fundus flavimaculatus (FFM) is one of the most frequent causes of macular degeneration in childhood. The disease is inherited as an autosomal recessive trait and the corresponding gene has been localized to chromosome 1p21-22 and subsequently identified as the ATP-binding cassette transporter (ABCR) gene. PURPOSE: To characterize Finnish and Swedish STGD families genetically, with special reference to chromosome region 1p21-22. METHODS: We performed genetic linkage and haplotype analyses in five families of Finnish and Swedish origin with members affected by STGD or FFM. RESULTS: Evidence for linkage between STGD and the ABCR gene region on chromosome 1p was found with a maximum cumulative two-point lod score for marker D1S188 (Z=4.04, theta=0.001). The affected individuals of all families, including the offspring of a consanguineous family, were found heterozygous for haplotypes spanning the ABCR gene. CONCLUSION: The results support genetic homogeneity for a STGD/FFM gene defect on chromosome 1p21-22. A variety of haplotypes tightly linked to the ABCR gene region were found among affected individuals which indicate the presence of several independent STGD mutations in the Scandinavian population.

ATP-Binding Cassette Transporters↗
PubMed1998

A gene encoding a liver-specific ABC transporter is mutated in progressive familial intrahepatic cholestasis.

The progressive familial intrahepatic cholestases (PFIC) are a group of inherited disorders with severe cholestatic liver disease from early infancy. A subgroup characterized by normal serum cholesterol and gamma-glutamyltranspeptidase (gammaGT) levels is genetically heterogeneous with loci on chromosomes 2q (PFIC2) and 18q. The phenotype of the PFIC2-linked group is consistent with defective bile acid transport at the hepatocyte canalicular membrane. The PFIC2 gene has now been identified by mutations in a positional candidate, BSEP, which encodes a liver-specific ATP-binding cassette (ABC) transporter, sister of p-glycoprotein (SPGP). The product of the orthologous rat gene has been shown to be an effective bile acid transporter in vitro. These data provide evidence that SPGP is the human bile salt export pump (BSEP).

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Evidence for digenic inheritance of nonsyndromic hereditary hearing loss in a Swedish family.

We investigated a Swedish family with nonsyndromic progressive bilateral sensorineural hearing loss. Thirteen candidate loci for autosomal dominant nonsyndromic hearing loss were tested for linkage in this family. We found significant LOD scores (>3) for markers at candidate locus DFNA12 (11q22-q24) and suggestive LOD scores (>2) for markers at locus DFNA2 (1p32). Our results for markers on chromosome 11 narrowed down the candidate region for the DFNA12 locus. A detailed analysis of the phenotypes and haplotypes shared by the affected individuals supported the notion that two genes segregated together with hearing impairment in the family. Severely affected family members had haplotypes linked to the disease allele on both chromosomes 1 and 11, whereas individuals with milder hearing loss had haplotypes linked to the disease allele on either chromosome 1 or chromosome 11. These observations suggest an additive effect of two genes, each gene resulting in a mild and sometimes undiagnosed phenotype, but both together resulting in a more severe phenotype.

Adult↗
PubMed1998

Identification of microdeletions spanning the Diamond-Blackfan anemia locus on 19q13 and evidence for genetic heterogeneity.

Diamond-Blackfan anemia (DBA) is a rare pure red-cell hypoplasia of unknown etiology and pathogenesis. A major DBA locus has previously been localized to chromosome 19q13.2. Samples from additional families have been collected to identify key recombinations, microdeletions, and the possibility of heterogeneity for the disorder. In total, 29 multiplex DBA families and 50 families that comprise sporadic DBA cases have been analyzed with polymorphic 19q13 markers, including a newly identified short-tandem repeat in the critical gene region. The results from DNA analysis of 29 multiplex families revealed that 26 of these were consistent with a DBA gene on 19q localized to within a 4.1-cM interval restricted by loci D19S200 and D19S178; however, in three multiplex families, the DBA candidate region on 19q13 was excluded from the segregation of marker alleles. Our results suggest genetic heterogeneity for DBA, and we show that a gene region on chromosome 19q segregates with the disease in the majority of familial cases. Among the 50 families comprising sporadic DBA cases, we identified two novel and overlapping microdeletions on chromosome 19q13. In combination, the three known microdeletions associated with DBA restrict the critical gene region to approximately 1 Mb. The results indicate that a proportion of sporadic DBA cases are caused by deletions in the 19q13 region.

Chromosome Mapping↗
PubMed1998

Characterization of the myotubularin dual specificity phosphatase gene family from yeast to human.

X-linked myotubular myopathy (XLMTM) is a severe congenital muscle disorder due to mutations in the MTM1 gene. The corresponding protein, myotubularin, contains the consensus active site of tyrosine phosphatases (PTP) but otherwise shows no homology to other phosphatases. Myotubularin is able to hydrolyze a synthetic analogue of tyrosine phosphate, in a reaction inhibited by orthovanadate, and was recently shown to act on both phosphotyrosine and phosphoserine. This gene is conserved down to yeast and strong homologies were found with human ESTs, thus defining a new dual specificity phosphatase (DSP) family. We report the presence of novel members of the MTM gene family in Schizosaccharomyces pombe, Caenorhabditis elegans, zebrafish, Drosophila, mouse and man. This represents the largest family of DSPs described to date. Eight MTM-related genes were found in the human genome and we determined the chromosomal localization and expression pattern for most of them. A subclass of the myotubularin homologues lacks a functional PTP active site. Missense mutations found in XLMTM patients affect residues conserved in a Drosophila homologue. Comparison of the various genes allowed construction of a phylogenetic tree and reveals conserved residues which may be essential for function. These genes may be good candidates for other genetic diseases.

Amino Acid Sequence↗
PubMed1997

Cloning and characterization of an alternatively spliced gene in proximal Xq28 deleted in two patients with intersexual genitalia and myotubular myopathy.

We have identified a novel human gene that is entirely deleted in two boys with abnormal genital development and myotubular myopathy (MTM1). The gene, F18, is located in proximal Xq28, approximately 80 kb centromeric to the recently isolated MTM1 gene. Northern analysis of mRNA showed a ubiquitous pattern and suggested high levels of expression in skeletal muscle, brain, and heart. A transcript of 4.6 kb was detected in a range of tissues, and additional alternate forms of 3.8 and 2.6 kb were present in placenta and pancreas, respectively. The gene extends over 100 kb and is composed of at least seven exons, of which two are noncoding. Sequence analysis of a 4.6-kb cDNA contig revealed two overlapping open reading frames (ORFs) that encode putative proteins of 701 and 424 amino acids, respectively. Two alternative spliced transcripts affecting the large open reading frame were identified that, together with the Northern blot results, suggest that distinct proteins are derived from the gene. No significant homology to other known proteins was detected, but segments of the first ORF encode polyglutamine tracts and proline-rich domains, which are frequently observed in DNA-binding proteins. The F18 gene is a strong candidate for being implicated in the intersexual genitalia present in the two MTM1-deleted patients. The gene also serves as a candidate for other disorders that map to proximal Xq28.

Alternative Splicing↗
PubMed1997

Progressive familial intrahepatic cholestasis (PFIC): evidence for genetic heterogeneity by exclusion of linkage to chromosome 18q21-q22.

Progressive familial intrahepatic cholestasis (PFIC) is the second most common form of familial intrahepatic cholestasis. The genes for PFIC and for a milder form of the disease, benign recurrent intrahepatic cholestasis (BRIC), were recently mapped to a 19-cM region on chromosome 18q21-q22. The results suggest that PFIC and BRIC are allelic diseases. We have studied 11 Swedish patients from eight families with clinical and biochemical features consistent with PFIC. The families were genotyped for markers D18S69, D18S64, D18S55 and D18S68, spanning the PFIC candidate region. Unexpectedly, the segregation of haplotypes excluded the entire region in three families, and no indications for shared haplotypes were found in the patients of the six remaining families. A four-point linkage analysis of all families excluded linkage from D18S69 to D18S55 (Zmax < -5). Thus, our data strongly suggest the presence of a second, yet unknown, locus for PFIC. The results indicate that great care should be taken when using 18q markers for prenatal diagnosis and genetic counseling for the disease.

Cholestasis, Intrahepatic↗