Mitochondrial DNA variant 11719G is a marker for the mtDNA haplogroup cluster HV

Based on sequencing data and results obtained from applying a tailored mismatch polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis, we report that the G allele of the mitochondrial DNA (mtDNA) polymorphism at nucleotide position 11719 is associated with the European mtDNA haplogroup cluster HV, and that 11719A is therefore the ancestral allele.

A new mitochondrial tRNA(Met) gene mutation in a patient with dystrophic muscle and exercise intolerance

A 30-year-old woman with a novel heteroplasmic U4409C mtDNA mutation in the tRNA(Met) gene presented with growth retardation, muscle weakness, severe exercise intolerance, and lactic acidosis. Muscle biopsy showed unusually severe dystrophic features. The mutation was not present in maternal relatives or 25 healthy subjects. Single-fiber PCR-RFLP analysis of mtDNA showed higher proportion of the mutation in COX-negative than in COX-positive muscle fibers.

A spectrum of mutations in the second gene for autosomal dominant polycystic kidney disease (PKD2)

Recently the second gene for autosomal dominant polycystic kidney disease (ADPKD), located on chromosome 4q21-q22, has been cloned and characterized. The gene encodes an integral membrane protein, polycystin-2, that shows amino acid similarity to the PKD1 gene product and to the family of voltage-activated calcium (and sodium) channels. We have systematically screened the gene for mutations by single-strand conformation-polymorphism analysis in 35 families with the second type of ADPKD and have identified 20 mutations. So far, most mutations found seem to be unique and occur throughout the gene, without any evidence of clustering. In addition to small deletions, insertions, and substitutions leading to premature translation stops, one amino acid substitution and five possible splice-site mutations have been found. These findings suggest that the first step toward cyst formation in PKD2 patients is the loss of one functional copy of polycystin-2.

Genetic heterogeneity of migraine with and without aura in Danes cannot be explained by mutation in mtDNA nucleotide pair 11084

INTRODUCTION

Migraine is a genetic heterogeneous disorder. The 11084 A to G base substitution is in the gene for the ND4 subunit of the respiratory complex I, and leads to a Thr to Ala amino acid replacement. This mutation had been found in 25% of Japanese migraineurs, while tension-type headache sufferers and non-migraineurs did not have it.

MATERIAL AND METHODS

We investigated the importance of this mutation in Danish migraineurs without aura, migraineurs with aura and non-migraineurs from the general population.

RESULTS

We did not detect this mutation in Danes.

CONCLUSION

Our result excludes a significant role of this mutation in the etiology of migraine in Denmark, and its absence in non-migraineurs supports that this mutation is rare in non-Japanese populations.

Quantification, by solid-phase minisequencing, of the telomeric and centromeric copies of the survival motor neuron gene in families with spinal muscular atrophy

In an analysis of 30 families affected by spinal muscular atrophy (SMA) we have used the solid-phase minisequencing method to determine the ratio between the number of telomeric and centromeric copies of the survival motor neuron gene (SMN and cBCD541 respectively) on normal and SMA chromosomes. This has enabled us to establish haplotypes with regard to SMN and cBCD541, and estimate their frequencies, on both types of chromosomes. Six predominant haplotypes were identified, three for normal chromosomes and three for SMA chromosomes, characterized by having 0, 1, or 2 copies, respectively, of cBCD541. We found evidence for the presence of patients homozygous for a deletion of SMN and with only one copy of cBCD541, but found none deleted for all copies of this gene. Several asymptomatic carriers of SMA with only a single copy of SMN and no copy of cBCD541 were identified. We could not confirm the hypothesis that the presence of more copies of cBCD541 is correlated to a less severe course of the disease. The frequencies of haplotypes characterized by having 0, 1, or 2 copies, respectively, of cBCD541 were found to differ significantly between normal and SMA chromosomes. This distribution can be explained by an underrepresentation of the haplotype completely lacking SMN genes, which is expected to cause early embryonic death in homozygotes. This first report of a direct haplotype analysis of SMN and cBCD541 should help clarify the role of cBCD541 in the pathogenesis of SMA.

[Hereditary optic nerve atrophy. A clinical-genealogical status over Danish families with Leber disease]

An update on Leber's hereditary optic neuropathy (LHON) in Denmark disclosed 32 families with at least one live affected member, or recent disease onset (Table 1). Mitochondrial DNA analysis in the 30 families available for blood sampling identified the pathogenic mutation in all of them: ND4/11778 (26 families), ND1/3460 (three families), and ND6/14484 (one family). A previous distinct male dominance (sex ratio 4.6:1 in 157 ND4-patients with onset before 1968) seems to level (sex ratio 2.6:1 in 69 ND4-patients with onset in 1968 or later). Among possible explanations, we discuss improved diagnostic abilities and possible changes in women's alcohol consumption and smoking habits.

Leber's hereditary optic neuropathy associated with a disorder indistinguishable from multiple sclerosis in a male harbouring the mitochondrial DNA 11778 mutation

This report describes a multiple sclerosis (MS)-like disorder in a male patient with Leber's hereditary optic neuropathy (LHON) harbouring the mitochondrial DNA 11778 base pair mutation. Given the population frequencies of MS and LHON, coincidental occurrence is unlikely. Hypothetically the mitochondrial mutation underlying LHON may contribute to presumably immunologically mediated involvement of other myelinated axons in the central nervous system in susceptible individuals, producing a disorder indistinguishable from MS. We recommend that investigation for oligoclonal bands in CSF, evoked potentials and MR brain scan in these patients be supplemented with mitochondrial DNA analysis.

[Genetic testing in occupational environmental context]

Individuals with an increased risk of occupationally and nonoccupationally induced adverse health effects may be identified by genetic monitoring and genetic screening. Genetic monitoring of induced genetic changes is performed by measurements of chromosomal aberrations or DNA-lesions. Genetic screening includes detection of inherited traits by measurements of enzyme activities in blood, the presence of a specific gene or a specific mutation. Inherited serum alpha-1-antitrypsin deficiency increases the risk of developing a chronic obstructive pulmonary disease. The risk is exacerbated by occupational exposure to dust. The available methods used for genetic screening of individual susceptibility to occupational exposures are not sufficiently validated for routine use. This is especially relevant concerning the population validity referring to how well the markers depict an event in a population. Legal and ethical aspects of preemployment genetic testing are currently discussed in Denmark.

A new human mtDNA polymorphism: tRNA(Gln)/4336 (T-->C)

We report the observation of a polymorphism in the human mitochondrial tRNA(Gln) gene. This polymorphism is detectable by both NlaIII and Sau961, whose recognition sequences overlap at the polymorphic base pair.

Juvenile Kearns-Sayre syndrome initially misdiagnosed as a psychosomatic disorder

We have investigated a 15 year old girl with progressive external ophthalmoplegia, including bilateral ptosis and retinal rod and cone cell dysfunction with atypical retinal pigmentation, complicated by cerebellar ataxia, partial cardiac conduction block, and diabetes mellitus. In infancy she had a severe crisis of bone marrow depression, and as a child she suffered from hypersensitivity to light, increasing fatigue, and vertigo, signs that were initially though to be psychosomatic. Histological examination showed mitochondrial myopathy, and subsequent mitochondrial DNA (mtDNA) analysis showed a deletion of approximately 5500 base pairs in 35 to 40% of her muscle mtDNA. We therefore conclude that this patient has developed the Kearns-Sayre syndrome after a Pearson syndrome-like crisis in her first year of life.

Chromosome 4 localization of a second gene for autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetically heterogeneous disorder. A gene defect located on the short arm of chromosome 16 is responsible for the disease in roughly 86% of affected European families. Using highly polymorphic microsatellite DNA markers, we have assigned a second gene for ADPKD to chromosome 4. In eight families with clear evidence against linkage to chromosome 16 markers, linkage analysis with the markers D4S231 and D4S423, demonstrated a multipoint lod score of 22.42.

Mutation-specific PCR: a rapid and inexpensive diagnostic method, as exemplified by mitochondrial DNA analysis in Leber's hereditary optic neuropathy

Mitochondrial DNA analyses were carried out on 30 individuals with clinically documented or suspected Leber's hereditary optic neuropathy (LHON). Three methods based on the polymerase chain reaction (PCR) were compared, all three aiming at detecting the G/C to A/T mutation of base pair 11,778 causing LHON. Two methods included restriction analysis with either Sfa NI or Mae III, while the third one relied on allele-specific amplification (ASA), using a mutation-specific primer. The results were completely consistent, showing the presence of the mutation in 18 and its absence in 12 cases. From these results it is concluded, that mutation-specific PCR is the diagnostic method of choice, because it obviates the need for subsequent restriction analysis, thus being faster and more cost-efficient. The general applicability of ASA makes this strategy universally useful for detection of specific mutations in the diagnostic analysis of genetic disease, and for typing of genetic polymorphisms or other sequence variations due to single-base differences.

Screening for the two most frequent mutations in Leber's hereditary optic neuropathy by duplex PCR based on allele-specific amplification

This report describes a rapid and inexpensive assay, which allows detection, in whole blood and by PCR alone, of the two most frequent mitochondrial DNA mutations causing Leber's hereditary optic neuropathy. The assay is based on allele-specific amplification, using primers with the mutation-specific base in the 3' position, and a deliberately introduced G-->C substitution of base no. four from the 3' end, which prevents amplification of the wild-type allele.

Mutation detection in Leber's hereditary optic neuropathy by PCR with allele-specific priming

An assay was designed that allows detection, by PCR alone, of the mutation of base pair no. 11,778 in human mitochondrial DNA, causing Leber's hereditary optic neuropathy. This was obtained by using a 20-mer primer with the mutation-specific base in the 3'-position, plus a deliberately introduced C/C-mismatch at base no. four from the 3'-end. The latter mismatch was necessary, and sufficient, to prevent amplification of the normal allele.

[Leber's hereditary optic atrophy. A hereditary disease caused by mitochondrial DNA mutation]

Leber's hereditary optic neuropathy is a genetic disorder characterized by sudden bilateral loss of vision. It is transmitted exclusively through females (matroclinous inheritance) due to a mutation in mitochondrial DNA (mtDNA), most frequently a GC----AT substitution of base pair no. 11778 ('The Wallace mutation'). All children of homoplasmic female carriers inherit the disease gene. Penetrance is incomplete, but high in males. Genetic heterogeneity has been reported, as has heteroplasmy. The nature of the mutation and the degree of heteroplasmy have prognostic value, and genetic counselling as well as clinical evaluation should therefore include mtDNA analysis. Diagnostic mtDNA analysis is illustrated for three Danish patients, one of whom is without known affected relatives. All three were homoplasmic for the Wallace mutation. Neither prophylaxis nor therapy, by medication are possible as yet. Loss of vision may be prevented, or delayed, if at-risk individuals refrain from smoking and consumption of certain foodstuffs.

Exclusion mapping of 12 X-linked disease loci and 10 DNA probes from the long arm of the X-chromosome

Specific chromosome rearrangements associated with disease entities are invaluable resources for physical mapping. A deletion on the X chromosome of a male leads to the nullisomy for X-linked genes, resulting in the onset of genetic diseases and/or the absence of the DNA probe detectable sequences. This permits the localization of these loci within the deleted area. On the other hand, the region for some other X-linked loci can be excluded from the deleted area according to the absence of the characteristic symptoms of the disease and/or the presence of the hybridization signals. An interstitial deletion on the long arm of the X chromosome of a male has been characterized by high resolution banding. The karyotype of the proband is 46,Y,del(X)(pter----q21.1::q21.33----qter). The regions for 12 X-linked disease loci as well as 10 DNA probes are excluded from the deleted area, and localized either proximally or distally to the deletion. The results also reveal a controversy in the present linkage data concerning the assignment of these loci.

A deletion panel of the long arm of the X chromosome: subregional localization of 22 DNA probes

Two males and two females with different but overlapping deletions on the proximal long arm of the X chromosomes have been investigated. Their karyotypes, which have been well characterized by high resolution banding techniques, are 46,Y,del(X)(pter----q21.1::q21.33----qter); 46,Y,del(X)(pter----q21.2::q21.31----qter); 46,X,del(X)(pter----q21.31::q24.3----qter) and 46,X,del(X)(pter----q21.1:). A deletion panel, which makes it possible to subdivide the long arm of the X chromosome into seven subregions, has been established using the genomic DNA from the four families, and applied to the fine subregional localization of the loci for 22 DNA probes. Based on the results obtained, the possible location of the loci in question has been narrowed down considerably, in some cases to an area of only 5% of the previously assigned region; hybridization to Southern blots of a panel with well-characterized chromosome deletions is thus a powerful means of localizing DNA probes, especially with respect to the X probes.

Autosomal dominant polycystic kidney disease in the 1980's

Since it is one of the commonest hereditary diseases, causing serious illness in adulthood, autosomal dominant polycystic kidney disease (ADPKD) is a problem for both the affected families and for the health economy of the society. The current management of ADPKD is reviewed with emphasis on the development of predictive DNA analyses, the recently discovered genetic heterogeneity, and ethical perspectives. Insurance aspects are discussed, and the need for access to selective reproductive prevention as well as for improvement of conventional therapeutic measures is stressed.

Assignment of the locus order DXS28-DXS67-DMD as a spin-off from diagnostic DNA marker analysis in a family with Duchenne muscular dystrophy

During diagnostic segregation analysis for seven DNA markers, linked to and flanking the locus for Duchenne muscular dystrophy (DMD), a family was identified in which a boy with a recombinant X chromosome had inherited his maternal grandmother's alleles at the loci DXS43 (D2/Pvu II) and DXS28 (C7/Eco RV), and his maternal grandfather's alleles at DXS67 (B24/Msp I) and DXS84 (754/Pst I). Combined with earlier data this finding strongly suggests the locus order DXS28-DXS67-DMD. Another recombination event, identified in the same family, supports the previously established order DMD-DXS84-OTC. The diagnostic importance of flanking markers, and the likelihood of false diagnostic conclusions due to possible double crossovers, with and without demonstrable neighbouring single crossover events, are discussed.

H-Y antigen. A hazard to the female?

In recent years a male-specific but species non-specific mammalian cell surface antigen, the H-Y antigen, has been demonstrated on somatic cells as well as on sperm. This raises some questions regarding unforeseen risks of certain medical procedures, notably blood transfusion. It is stressed that especially the possible bearing of immunization against H-Y antigen on female fertility should be considered, and it is suggested that transfusion of blood cells from males into females should be avoided. Furthermore it is suggested that the risk for contamination of non-oral viral vaccines with host cell H-Y antigen is considered, and it is proposed that as a preventive measure with viruses should be grown in female cell cultures.

Nomenclature of GM2-gangliosidoses

As a supplement to the recently proposed systematic nomenclature for the genotypes and phenotypes of GM2-gangliosidoses (O'Brien 1978b), it is suggested that guidelines be adopted for the use of eponyms and type designations in connection with this group of sphingolipidoses. The biochemical genetics of the lysosomal beta-hexosaminidase system in man are briefly reviewed, and recommendations are proposed for the use of eponyms and type designations based upon a locus-oriented framework.