Effect of insulin resistance, apoE2 allele, and smoking on combined hyperlipidemia

Combined hyperlipidemia may result from the interaction of several metabolic and environmental factors. We explored to what extent fasting insulin concentration, apolipoprotein (apo) E2 frequency, and cigarette smoking explained the serum levels of triglyceride and high-density lipoprotein cholesterol (HDL-C) in patients with combined hyperlipidemia. Forty-nine untreated patients with combined hyperlipidemia were compared with 49 hypercholesterolemic patients who were matched for gender, age, and body mass index. All laboratory values were obtained after 9 weeks of standardized dietary intake and after an overnight fast. The patients with combined hyperlipidemia had a significantly higher (33 pmol/L, 50%) mean insulin concentration than matched hypercholesterolemic control subjects, indicating that the combined hyperlipidemic patients were more insulin resistant. However, the differences in the fasting insulin and triglyceride concentrations within the pairs were only slightly correlated (adjusted r = .29). The combined hyperlipidemic patients were also characterized by a higher frequency of apoE2 alleles (25% versus 6%) and smokers (41% versus 16%). In a matched multiple linear regression model, the differences in insulin concentration, apoE2 allele frequency, and smoking explained 12%, 8%, and 9%, respectively, of the mean paired difference in triglyceride concentration. The differences in insulin concentration or apoE2 allele frequency did not significantly explain the mean paired difference in HDL-C concentration, whereas smoking explained 17% of the difference. In conclusion, fasting insulin concentration, the presence of the apoE2 allele, and smoking may explain 30% of the hypertriglyceridemia and the low levels of HDL-C in nonobese patients with combined hyperlipidemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Variable expression of familial dysbetalipoproteinemia in apolipoprotein E*2 (Lys146-->Gln) Allele carriers

Genetic and biochemical studies were carried out in 96 relatives of six independently ascertained probands with familial dysbetalipoproteinemia (FD) carrying the APOE*2 (Lys146-->Gln) allele. Compared to noncarriers, the 40 heterozygous APOE*2 (Lys146-->Gln) allele carriers exhibited markedly increased mean levels of cholesterol and triglyceride in the very low density lipoproteins (VLDL) (1.89 +/- 0.37 vs 0.30 +/- 0.27 and 1.86 +/- 0.37 vs 0.68 +/- 0.27 mmol/liter, respectively) and plasma apolipoprotein (apo) E levels (28.1 +/- 1.6 vs 4.6 +/- 1.1 mg/dl), which is characteristic for FD. By means of a pedigree-based maximum likelihood method we calculated that carrier-status accounted for 57% and 71%, respectively, of the total variance of the ratio (VLDL + IDL)-cholesterol/plasma triglyceride and plasma apoE levels. APOE*2 (Lys146-->Gln) and APOE*3-Leiden allele carriers were found to differ significantly in: (a) plasma apoE levels, (b) in the amounts of triglycerides in the VLDL and VLDL + IDL fraction, and (c) in the amount of cholesterol in the VLDL and VLDL + IDL fraction relative to the amount of triglyceride in these fractions. In the APOE*2 (Lys146-->Gln) allele carriers the VLDL and VLDL + IDL fraction is relatively rich in triglycerides as compared with that in APOE*3-Leiden carriers. We hypothesize that these two rare mutations of apoE both lead to dominantly inherited forms of FD along different underlying metabolic defects.

Linkage of autosomal dominant hearing loss to the short arm of chromosome 1 in two families

BACKGROUND

At least half of the cases of profound deafness of early onset are caused by genetic factors, but few of the genetic defects have been identified. This is particularly true of the most common hereditary forms of deafness, which occur in the absence of any associated syndrome.

METHODS

We studied a large Indonesian family in which hearing loss was inherited in an autosomal dominant pattern. The hearing loss first affects the high frequencies during the teens or 20s and becomes profound within 10 years. To locate the responsible gene, we performed genetic-linkage analysis, using microsatellite markers distributed over the entire genome. We then performed linkage analyses in an American family and a Dutch family with similar patterns of hereditary hearing loss.

RESULTS

In the extended Indonesian family, a gene linked to deafness mapped to chromosome 1p, with a multipoint lod score of more than 7. In the American family, deafness was linked to the same locus on chromosome 1p, with a multipoint lod score of more than 5. In the Dutch family, however, this locus was ruled out. The flanking markers D1S255 and D1S211 defined a region of 6 cM on chromosome 1p that is likely to contain the gene associated with deafness in the first two families.

CONCLUSIONS

In some families with early-onset autosomal dominant hearing loss, the responsible gene is on chromosome 1p.

Familial hemiplegic migraine in The Netherlands. Dutch Migraine Genetics Research Group

In this article we describe two Dutch families with familial hemiplegic migraine (FHM). In one family FHM co-segregated with cerebellar ataxia. We discuss the relevance of the genetics of FHM for the research into the genetics of 'normal' migraine with or without aura.

Genetic heterogeneity of familial hemiplegic migraine

Familial hemiplegic migraine (FHM) is a distinctive form of migraine with an autosomal dominant mode of inheritance. The migraine-like attacks are associated with transient hemiparesis. A locus for FHM has recently been assigned to chromosome 19 by linkage mapping. In the present study, five unrelated pedigrees with multiple members suffering from hemiplegic migraine were investigated. In two of the pedigrees additional symptoms, cerebellar ataxia and benign neonatal convulsions, respectively, were observed in affected members. Three pedigrees showed linkage to loci D19S391, D19S221, and D19S226 at chromosome 19p13. Haplotyping suggested a location of a FHM gene between D19S391 and D19S221. In the two remaining families, evidence against linkage was found. These results confirm the localization of a gene for familial hemiplegic migraine to the short arm of chromosome 19, but locus heterogeneity not corresponding to the observed clinical heterogeneity is likely to exist.

The apolipoprotein C2-linked (Acl) gene: a new gene within the mouse apolipoprotein e-c1-c2 gene cluster

The apolipoprotein E, C1, and C2 genes are contained within a gene cluster in man. Previously, we have shown that this gene cluster has a similar structure in mouse. During the characterization of the mouse Apoc2 gene, evolutionarily conserved and transcribed sequences were found 5' of the Apoc2 gene. In this study, we have shown that these 5' sequences represent a novel gene within the gene cluster designated the apolipoprotein C2-linked gene (Acl). The Acl gene is located 2 kb 5' to the Apoc2 gene. The transcriptional orientation is identical to that of the other genes within the Apoe-c1-c2 gene cluster. We have sequenced the mouse Acl gene at the cDNA and the genomic levels. The gene is composed of three exons spanning a region of approximately 3.6 kb. The Acl gene is expressed in the liver as a transcript 473 bp in size and encodes a putative protein of 124 amino acid residues.

Pure hereditary spastic paraparesis: an exclusion map covering more than 40% of the autosomal genome

Pure hereditary spastic paraparesis (HSP) is an upper motor neuron syndrome clinically characterized by slowly progressive weakness and spasticity of the legs. To determine the chromosomal location of the genetic defect, a five-generational Dutch family with autosomal dominant pure HSP was subjected to linkage studies. Analysis was carried out on 48 members spanning three generations, of whom 23 individuals are definitely affected. By screening the genome with a total of 167 microsatellite markers distributed over all autosomes, an exclusion map for HSP was constructed. Depending on the actual size of the human genome, our exclusion map covered between 40% and 65% of its autosomal length. Loci on chromosomes 1, 8, 13, 14, and 18 showed slightly positive lod scores. The areas around these loci were investigated more closely, but no conclusive evidence for, or against, linkage could be obtained.

Facioscapulohumeral muscular dystrophy in early childhood

OBJECTIVE

To determine the occurrence and the clinical and genetic variability of early-onset facioscapulohumeral muscular dystrophy (FSHD).

DESIGN

Patients were derived from a large series of patients who participated in a genetic study of FSHD in the Netherlands.

PATIENTS

A group of 96 patients of 17 families with autosomal dominant FSHD, nine sporadic cases of FSHD, and 35 children at risk for having the FSHD gene was searched for the presence of early-onset cases. Criteria for early-onset FSHD were (1) signs or symptoms of facial weakness before the age of 5 years and (2) signs or symptoms of shoulder girdle weakness before the age of 10 years.

RESULTS

Six early-onset cases (four familial, two sporadic) were identified. Four of five cases showed an abnormal DNA fragment with the probe p13E-11, which has been shown to detect DNA rearrangements in FSHD patients. The clinical symptoms in these early-onset cases showed great variability with respect to rate of progression of muscle weakness, the association of hearing loss and retinopathy, and the expression of the disorder in parents and siblings.

CONCLUSIONS

Infantile FSHD has been suggested to be a separate form of the disease, often accompanied by sensorineural hearing loss and retinal telangiectasia. Our findings, as well as the fact that both hearing loss and retinal vasculopathy have been recently shown to be part of FSHD, suggest that early-onset FSHD is not a separate entity, but part of a wide clinical spectrum of FSHD.

Diet-induced hyperlipoproteinemia and atherosclerosis in apolipoprotein E3-Leiden transgenic mice

Apolipoprotein E3-Leiden (APOE*3-Leiden) transgenic mice have been used to study the effect of different cholesterol-containing diets on the remnant lipoprotein levels and composition and on the possible concurrent development of atherosclerotic plaques. On high fat/cholesterol (HFC) diet, the high expressing lines 2 and 181 developed severe hypercholesterolemia (up to 40 and 60 mmol/liter, respectively), whereas triglyceride levels remained almost normal when compared with regular mouse diet. The addition of cholate increased the hypercholesterolemic effect of this diet. In lines 2 and 181, serum levels of apo E3-Leiden also increased dramatically upon cholesterol feeding (up to 107 and 300 mg/dl, respectively). In these high expressing APOE*3-Leiden transgenic mice, the increase in both serum cholesterol and apo E3-Leiden occurred mainly in the VLDL/LDL-sized fractions, whereas a considerable increase in large, apo E-rich HDL particles also occurred. In contrast to the high expressing lines, the low expressing line 195 reacted only mildly upon HFC diet. On HFC diets, the high expresser APOE*3-Leiden mice developed atherosclerotic lesions in the aortic arch, the descending aorta, and the carotid arteries, varying from fatty streaks containing foam cells to severe atherosclerotic plaques containing cholesterol crystals, fibrosis, and necrotic calcified tissue. Quantitative evaluation revealed that the atherogenesis is positively correlated with the serum level of cholesterol-rich VLDL/LDL particles. In conclusion, with APOE*3-Leiden transgenic mice, factors can be studied that influence the metabolism of remnant VLDL and the development of atherosclerosis.

Lipoprotein profiles in a family with two mutants of apolipoprotein E: possible association with hypertriglyceridaemia but not with dysbetalipoproteinaemia

1. The plasma lipoprotein profiles of eight members of a Dutch pedigree spanning three generations where two rare apolipoprotein E mutants, APOE*3(Cys-112-->Arg; Arg-251-->Gly) and APOE*2(Val-236-->Glu), segregate were analysed to determine whether the APOE mutants were associated with dyslipidaemia. 2. The proband, a 51-year-old Caucasian male, was a carrier of APOE*3(Cys-112-->Arg; Arg-251-->Gly) and his spouse was a carrier of APOE*2(Val-236-->Glu). Four other family members were carriers of one or both of the mutant APOE genes. 3. The plasma cholesterol and triacylglycerol concentrations were markedly elevated in the proband and were classified as type IV hyperlipoproteinaemia. The plasma triacylglycerol concentration was moderately increased in a sister, who was a carrier of APOE*3(Cys-112-->Arg; Arg-251-->Gly), and in the son, who was a compound heterozygote for both mutant APOE alleles. Normal plasma lipid levels were observed in all other family members. In the plasma samples of the proband and his family members beta-very-low-density lipoprotein was not detectable and the molar ratio of very-low-density lipoprotein-cholesterol to very-low-density lipoprotein-triacylglycerol was less than 0.9. The concentration of intermediate-density lipoprotein was within normal limits. 4. None of the family members carrying APOE*3-(Cys-112-->Arg; Arg-251-->Gly) and/or APOE*2(Val-236-->Glu) exhibited lipoprotein abnormalities characteristic of familial dysbetalipoproteinaemia, although three family members carrying APOE*3-(Cys-112-->Arg; Arg-251-->Gly) showed hypertriglyceridaemia.

Dominant congenital benign spinal muscular atrophy

The affected members of the family described in this article exhibit congenital nonprogressive atrophy and weakness of lower limb muscles in association with contractures. Clinical and laboratory findings support a dominant lower motor neuron disorder. DNA analysis excluded linkage of the disease with SMA markers on the long arm of chromosome 5. The condition must be differentiated from congenital and infantile SMA, from "arthrogryposis multiplex congenita, distal type," and from non hereditary types of congenital arthrogryposis.

Genetic heterogeneity of apolipoprotein E and its influence on plasma lipid and lipoprotein levels

Apolipoprotein E (apoE) is one of the major protein constituents of chylomicron and very-low-density lipoprotein (VLDL) remnants and plays a central role as a ligand in the receptor-mediated uptake of these particles by the liver. Including the most common variant, apoE3, 30 apoE variants have been characterized. At present, 14 apoE variants have been found to be associated with familial dysbetalipoproteinemia, a genetic lipid disorder characterized by elevated plasma cholesterol and triglyceride levels and an increased risk for atherosclerosis. Seven apoE variants were found to be associated with other forms of hyperlipoproteinemia. This report presents an overview of all currently known apoE variants and their effects on lipoprotein metabolism.

Pulsed-field gel electrophoresis of the D4F104S1 locus reveals the size and the parental origin of the facioscapulohumeral muscular dystrophy (FSHD)-associated deletions

Recently, probe p13E-11 (D4F104S1) was shown to identify de novo DNA rearrangements, which are associated with the development of facioscapulohumeral muscular dystrophy (FSHD). These rearrangements are likely to become instrumental in cloning the FSHD gene itself. Analysis by pulsed-field gel electrophoresis demonstrates that p13E-11 recognizes two highly polymorphic loci, with HindIII restriction fragments ranging in size from about 30 to 320 kb. Haplotype analysis unambiguously assigned one of the two loci to chromosome 4q35. The detection of identical NotI or NruI fragments with both CEB8 (D4F35S1) and p13E-11 demonstrated that the DNA rearrangements are deletions that are restricted to the HindIII fragments detectable by p13E-11. In two cases, the sizes of the deletion could be established and were found to be 25 and 85 kb in length, respectively. So far, we have been able to define the parental origin of the mutation in seven different patients and have found that in five cases the maternal allele was involved.

Inefficient degradation of triglyceride-rich lipoprotein by HepG2 cells is due to a retarded transport to the lysosomal compartment

Binding studies at 37 degrees C showed that lipoprotein lipase-treated very low density lipoproteins (LPL-VLDL) and very low density lipoproteins (VLDL), once taken up via the low density lipoprotein (LDL) receptor, are poorly degraded by HepG2 cells as compared with LDL. Determination of the initial endocytotic rate for LPL-VLDL and VLDL as compared to LDL shows that LPL-VLDL and VLDL are internalized at a similar rate as LDL. Incubation of cells with labeled LDL, LPL-VLDL, and VLDL at 18 degrees C for 4.5 h resulted in the accumulation of these particles in the early endosomes, without subsequent transport to the lysosomes and degradation. After washing the cells and a temperature shift to 37 degrees C, the labeled LDL present in the early endosomes is transported to the lysosomal compartment almost completely within 15 min. Strikingly, for LPL-VLDL and for VLDL, only about 50% or less of the label was moved to the lysosomal compartment within 45 min. However, once present in the lysosomes, VLDL and LPL-VLDL are degraded about 1.6-fold more rapidly than LDL. Retroendocytosis accounts for less than 10% of the internalized LDL, whereas a higher rate of retroendocytosis, up to 20 and 40%, respectively, was observed for LPL-VLDL and VLDL. To evaluate the effect of the inefficient transport of VLDL and LPL-VLDL to the lysosomal compartment on cellular cholesterol homeostasis, acyl-CoA:cholesterol acyltransferase (ACAT) activity was measured. Incubation with 30 micrograms/ml of LDL induced a 2.5-fold increase in ACAT activity, whereas the incubation with similar amounts of both VLDL and LPL-VLDL failed to stimulate this enzyme. We conclude that both a slower transport to the lysosomal compartment and a higher rate of retroendocytosis, possibly as the consequence of the longer residence time in the early endosomes, are responsible for the poor degradation of VLDL and LPL-VLDL by HepG2 cells.

An acceptor splice site mutation in intron 16 of the low density lipoprotein receptor gene leads to an elongated, internalization defective receptor

In this report, we describe the characterization of a mutation in the low density lipoprotein (LDL) receptor gene of a true homozygous familial hypercholesterolemic (FH) patient. The combined use of denaturing gradient gel electrophoresis (DGGE) and DNA sequence analysis revealed a unique A to G transition in the penultimate 3'-nucleotide of intron 16 of the LDL receptor gene, which disrupts the acceptor splice site. cDNA sequence analysis indicated that a cryptic splice site was activated in intron 16, upstream from the original splice site, leading to the inclusion of 62 nucleotides and a reading frame-shift. The resulting new translation product contains a stretch of 154 amino acids at the carboxy-terminal that have no resemblance to the normal receptor protein. To elucidate the biological effects of the mutation, the structural and functional properties of the mutated LDL receptor protein were studied. Immunoprecipitation of the newly synthesized LDL receptors showed that an aberrant precursor form of the LDL receptor protein was synthesized, about 10 kDa larger than normal, which is not further processed to the mature form. Some 50% of the normal LDL binding activity was found on the cell surface of the patient's fibroblasts, whereas internalization and degradation of LDL were abolished.

FSHD associated DNA rearrangements are due to deletions of integral copies of a 3.2 kb tandemly repeated unit

Facioscapulohumeral muscular dystrophy (FSHD) is a neuromuscular disorder characterized by progressive weakness of the facial, shoulder and upper arm muscles. The disease is associated with DNA rearrangements which are detectable using probe p13E-11 (D4F104S1) in DNA digested with EcoRI or other restriction enzymes. We have cloned and characterized the rearranged EcoRI fragment of four unrelated FSHD patients. Restriction fragment mapping and DNA sequence analysis showed that the proximal and distal parts of the EcoRI fragment, which flank a region of tandemly repeated 3.2 kb units, are identical in normal and rearranged EcoRI fragments. These results strongly support the hypothesis that the FSHD associated rearrangements are due to deletions of integral copies of the 3.2 kb repeated unit. Since these repeated units are likely to form part of the FSHD transcription unit, the variation in repeat unit number might affect the function of the gene product. Hence, our data confine the FSHD gene region and thus provide a starting point for cloning the FSHD gene.

A parent-twin study of plasma levels of histidine-rich glycoprotein (HRG)

Histidine-rich glycoprotein (HRG) is a non-enzymatic glycoprotein that acts as a modulator of several plasma proteins involved in coagulation and fibrinolysis. The contributions of genetic and environmental influences to inter-individual variation in plasma levels of HRG were studied in 160 Dutch families consisting of adolescent twin pairs and their parents. Results showed that 69% of the variance in plasma HRG concentrations could be accounted for by genetic factors. Heritability was the same in males and females and in parents and their offspring. There was no association between HRG levels of husband and wife and no evidence was found for the influence of shared family environment on the resemblance between relatives.

The mouse apolipoprotein C1 gene: structure and expression

We have isolated and characterized cDNA and genomic clones containing the mouse apolipoprotein C1 (Apoc1) gene. The Apoc1 gene is part of the Apoe-c1-c2 gene cluster and is located 3.4 kb 3' of the Apoe gene. The mouse Apoc1 gene spans a region of approximately 3.3 kb and consists of four exons. The exon-intron structure is similar to those of human and baboon genes, although in mouse introns 2 and 3 are smaller. Significant sequence homology is found between man and mouse in the promoter and exonic regions (80 and 67%, respectively). Northern blotting and primer extension analysis of mouse RNA showed that a major transcript 409 bp in size is expressed primarily in fetal and adult liver. The mouse Apoc1 cDNA contains an open reading frame encoding a protein of 88 amino acids, including a signal peptide of 26 amino acid residues. Comparisons of the deduced amino acid sequence of mouse apoC1 with the human, baboon, rat, and dog sequences showed discrete regions with a high degree of conservation. The delineation of the sequence and structural organization of the mouse Apoc1 gene is an essential step in enhancing the use of mouse models to study the function of apoC1 in the lipoprotein metabolism.

Physical mapping and YAC-cloning connects four genetically distinct 4qter loci (D4S163, D4S139, D4F35S1 and D4F104S1) in the FSHD gene-region

We have constructed a long-range restriction map of the region on chromosome 4q that contains the gene for facioscapulohumeral muscular dystrophy (FSHD). This region contains the linkage group cen ... D4S163-D4S139-D4F35S1-D4F104S1-FSHD ... 4qter, which spans a genetic distance of about 5 cM. Pulse field gel electrophoresis (PFGE) mapping indicated that these loci span a region not more than 1 Mb. STSs were developed for several of these loci, which served to isolate four overlapping yeast artificial chromosomes (YACs). These YACs confirmed the PFGE map and have allowed us to generate a more detailed restriction map using cosmid contig mapping. The physical distances were smaller than was expected on the basis of the genetic map. Two potential HTF islands have been detected within the cloned region. One HTF island maps about 100 kb centromeric from the tandem repeats involved in the FSHD mutation, whereas the other maps within these tandem repeats.

Fine mapping of the FSHD gene region orientates the rearranged fragment detected by the probe p13E-11

We have produced a fine restriction map around the locus D4F104S1 (previously designated D4S810); a probe to this locus, p13E-11, identifies a polymorphic EcoRI fragment containing 3.2kb tandem repeats and detects DNA rearrangements associated with facioscapulohumeral muscular dystrophy (FSHD). We developed an STS (D4F106S1) which maps 2kb proximal to D4F104S1, and used this to isolate a 470kb YAC (y25C2E) from the ICI YAC library and a 930kb YAC (y956A11) from the CEPH megabase library. Both YACs contain the loci D4S139, D4F35S1 and D4F104S1. A cosmid library was produced from YAC y25C2E and two cosmid contigs constructed; a 115kb contig encompassing D4S139, and one of 135kb linking D4F35S1 and D4F104S1 and extending distal to the EcoRI fragment detected by p13E-11. A fine restriction map of both these contigs has been generated, allowing the orientation of the EcoRI fragment rearranged in FSHD to be determined. YAC y956A11 was used to confirm the integrity of y25C2E and the map of this region. 9B6A, a probe to the homeobox region of the tandem repeat D4Z4, identified a cross-hybridising sequence proximal to D4F104S1, however, p13E-11 does not detect this additional locus. CpG islands were identified between D4S139 and D4F35S1 and within each copy of the tandem repeat. The probe 9B6A detected each copy of the repeat motif, suggesting there is homeobox present in every copy of the 3.2kb repeat.

The human skeletal muscle adenine nucleotide translocator gene maps to chromosome 4q35 in the region of the facioscapulohumeral muscular dystrophy locus

Facioscapulohumeral muscular dystrophy (FSHD) is a relatively common autosomal dominant neuromuscular disorder. The gene for FSHD has recently been assigned to chromosome 4q35. Although abnormal mitochondrial and biochemical changes have been observed in FSHD, the molecular defect is unknown. In addition to the FSHD gene, the human muscle adenine nucleotide translocator gene (ANT1) is located on chromosome 4. Interestingly, biochemical studies recently showed a possible defect of ANT1. In order to evaluate the potential role of ANT1 in the etiology of FSHD, the human ANT1 gene was isolated by cosmid cloning and localized to 4q35, in the region containing the FSHD gene. However, in situ hybridization and physical mapping of somatic cell hybrids localized the ANT1 gene proximal to the FSHD gene. In addition, a polymorphic CA-repeat 5 kb upstream of the ANT1 gene was used as a marker in FSHD and Centre d'Etude du Polymorphisme Humain families to perform linkage analysis. These data together exclude ANT1 as the primary candidate gene for FSHD. The most likely order of the loci on chromosome 4q35 is cen-ANT1-D4S171-F11-D4S187-D4S163-D4S139-+ ++FSHD-tel.

Molecular genetics of facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant neuromuscular disorder. The disease affects specific muscles of the face, shoulder-girdle and upper arm. The biochemical defect underlying FSHD is unknown and there are no specific tests that are diagnostic of FSHD. Genetic linkage studies have mapped the FSHD gene to chromosome 4q35. A DNA marker (p13E-11; D4F104S1, formerly D4S810) has been isolated which recognizes two highly polymorphic loci detectable by EcoRI or HindIII; one locus maps to chromosome 4q35 and shows fragments between about 50 and 320 kb. In FSHD patients deletions occur within this EcoRI/HindIII fragment, yielding fragments that are usually smaller than 28 kb. Characterization of the polymorphic fragments demonstrates that they consist of a 3.2 kb tandem repeat; their number can range between approximately 12 and 96 within the 4q35-specific fragments. In FSHD patients, an integral number of these tandem repeats are deleted, leaving at maximum eight copies.

PCR-based microsatellite polymorphisms in the detection of loss of heterozygosity in fresh and archival tumour tissue

PCR-based microsatellite polymorphisms have proved their power in genetic linkage analysis and other identification methods, due to their high information content and even distribution over the chromosomes. In the present study we applied microsatellite polymorphisms to detect loss of heterozygosity in fresh (snap-frozen) and in archival ovarian tumour tissue. Clear allele losses were found in fresh and paraffin embedded tumour samples. Conventional Southern analysis of flanking markers on the same tumour DNA samples confirmed the observed losses detected by microsatellite polymorphisms. Titration experiments suggest that loss of heterozygosity remains detectable in tumour samples despite 60% contamination with normal DNA. This technique provides a fast and reproducible alternative to conventional Southern blotting in the detection of loss of heterozygosity, with the crucial additional advantages of minimal sample requirements, making archival material available for genetic investigation.