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Biomedical subjects

M Farrall

Publications and source records attributed to M Farrall.

At least 37 records · Page 2Linked to original sources
PubMed1996

Angiotensinogen in human essential hypertension.

The candidacy of angiotensinogen for a role in the genetic basis of hypertension is supported by the observation that plasma angiotensinogen levels track with raised blood pressure through families. In addition, transgenic mice with overexpression of a rat angiotensinogen gene develop hypertension, and knockout mice with a disrupted gene and absent angiotensinogen production develop low blood pressure. There are now two studies in populations of white European origin and one in African Caribbeans providing support for a role of the angiotensinogen gene locus in human essential hypertension.

Angiotensinogen↗
PubMed1995

An extension of the Maximum Lod Score method to X-linked loci.

The Maximum Lod Score method for affected relative-pair analysis, introduced by Risch, is a powerful method for detecting linkage between an autosomal marker locus and disease. In order to use the method to detect linkage to markers on the X-chromosome, some modification is necessary. Here we extend the method to be applicable to X-chromosomal data, and derive genetic restrictions on the haplotype-sharing probabilities analogous to the 'possible triangle' restrictions described by Holmans for the autosomal case. Size criteria are derived using asymptotic theory and simulation, and the power is calculated for a number of possible underlying models. The method is applied to data from 284 type 1 diabetic families and evidence is found for the presence of one or more diabetogenic loci on the X-chromosome.

Alleles↗
PubMed1995

Linkage of the angiotensinogen gene locus to human essential hypertension in African Caribbeans.

The renin-angiotensin system regulates blood pressure and sodium balance. The angiotensinogen gene which encodes the key substrate within this system has been linked to essential hypertension in White Europeans. It has been suggested that people of West African ancestry may have a different genetic basis for hypertension. In this study we have tested whether there is linkage of the angiotensinogen gene to essential hypertension in African Caribbeans from St. Vincent and the Grenadines. DNA from 63 affected sibling pairs with hypertension was tested for linkage by analyzing whether there was excess allele sharing among siblings genotyped using an angiotensinogen dinucleotide repeat sequence. There was significant support for linkage (T = 3.07, P = 0.001) and association of this locus to hypertension (chi 2 = 50.2, 12 degrees of freedom, P << 0.001). A DNA polymorphism which alters methionine to threonine at position 235 (M235T) within the angiotensinogen peptide has been associated previously with hypertension. However, we found no association of this variant with hypertension in this study. These findings provide support for linkage and association of the angiotensinogen locus to hypertension in African Caribbeans and suggest some similarities in the genetic basis of essential hypertension in populations of different ethnicity.

Adult↗
PubMed1995

Two-locus maximum lod score analysis of a multifactorial trait: joint consideration of IDDM2 and IDDM4 with IDDM1 in type 1 diabetes.

To investigate the genetic component of multifactorial diseases such as type 1 (insulin-dependent) diabetes mellitus (IDDM), models involving the joint action of several disease loci are important. These models can give increased power to detect an effect and a greater understanding of etiological mechanisms. Here, we present an extension of the maximum lod score method of N. Risch, which allows the simultaneous detection and modeling of two unlinked disease loci. Genetic constraints on the identical-by-descent sharing probabilities, analogous to the "triangle" restrictions in the single-locus method, are derived, and the size and power of the test statistics are investigated. The method is applied to affected-sib-pair data, and the joint effects of IDDM1 (HLA) and IDDM2 (the INS VNTR) and of IDDM1 and IDDM4 (FGF3-linked) are assessed with relation to the development of IDDM. In the presence of genetic heterogeneity, there is seen to be a significant advantage in analyzing more than one locus simultaneously. Analysis of these families indicates that the effects at IDDM1 and IDDM2 are well described by a multiplicative genetic model, while those at IDDM1 and IDDM4 follow a heterogeneity model.

Diabetes Mellitus, Type 1↗
PubMed1995

Absence of genetic linkage between polymorphisms of the insulin receptor gene and essential hypertension.

This study evaluated whether hypertensive siblings had excess sharing of RsaI and SstI alleles of the insulin receptor gene compared with a random population. Thirty families consisting of 60 affected individuals with established hypertension were genotyped for the RsaI and SstI restriction fragment length polymorphisms and the resulting genotype data was analysed using the affected pedigree member method of linkage analysis. The hypertensive siblings were found to have increased sharing of INSR alleles; however, this linkage could not be confirmed using a maximum LOD score method. Thus, the results from this study do not support a role for the INSR gene in the genesis of essential hypertension in the population studied.

Aged↗
PubMed1995

Segregation and linkage analysis of serum angiotensin I-converting enzyme levels: evidence for two quantitative-trait loci.

Human serum angiotensin I-converting enzyme (ACE) levels vary substantially between individuals and are highly heritable. Segregation analysis in European families has shown that more than half of the total variability in ACE levels is influenced by quantitative-trait loci (QTL). One of these QTLs is located within or close to the ACE locus itself. Combined segregation/linkage analysis in a series of African Caribbean families from Jamaica shows that the ACE insertion-deletion polymorphism is in moderate linkage disequilibrium with an ACE-linked QTL. Linkage analysis with a highly informative polymorphism at the neighboring growth-hormone gene (GH) shows surprisingly little support for linkage (LOD score [Z] = 0.12). An extended analysis with a two-QTL model, where an ACE-linked QTL interacts additively with an unlinked QTL, significantly improves both the fit of the model (P = .002) and the support for linkage between the ACe-linked QTL interacts additively with an unlinked QTL, significantly improves both the fit of the model (P = .002) and the support for linkage between the ACe-linked QTL and GH polymorphism (Z = 5.0). We conclude that two QTLs jointly influence serum ACE levels in this population. One QTL is located within or close to the ACE locus and explains 27% of the total variability; the second QTL is unlinked to the ACE locus and explains 52% of the variability. The identification of the molecular mechanisms underlying both QTLs is necessary in order to interpret the role of ACE in cardiovascular disease.

Analysis of Variance↗
PubMed1994

Linkage of the angiotensinogen gene to essential hypertension.

BACKGROUND: The renin-angiotensin system is a powerful pressor system with a major influence on salt and water homeostasis. Angiotensinogen (also called renin substrate) is a key component of this system; it is cleaved by renin to yield angiotensin I, which is then cleaved by angiotensin-converting enzyme to yield angiotensin II. The observation that plasma angiotensinogen levels correlate with blood pressure and track through families suggests that angiotensinogen may have a role in essential hypertension. We therefore investigated whether there is linkage between the angiotensinogen gene on chromosome 1q42-43 and essential hypertension. METHODS: Samples of DNA from 63 white European families in which two or more members had essential hypertension were tested for linkage of the angiotensinogen gene to this disorder. Affected cousins, nephews, nieces, and half-siblings were included when possible. To test for linkage, we used as a marker a dinucleotide-repeat sequence flanking this gene, and we employed the affected-pedigree-member method of linkage analysis. Two molecular variants of the angiotensinogen gene, one encoding threonine instead of methionine at position 235 (M235T) and the other encoding methionine rather than threonine at position 174 (T174M), were also tested for possible association with essential hypertension. RESULTS: We found significant linkage (t = 5.00, P < 0.001) and association (chi-square = 53.3, P < 0.001) of the angiotensinogen-gene locus to essential hypertension in the 63 multiplex families. This linkage was consistently maintained in the subgroup of subjects with diastolic pressure above 100 mm Hg and in the subgroups classified according to sex. It has been proposed previously that T174M and M235T are associated with essential hypertension. However, we found no association in our population between either polymorphism and this disorder. CONCLUSIONS: This study provides strong and consistent support for the linkage to essential hypertension of regions within or close to the angiotensinogen gene. Precisely how mutations in this region may result in hypertension remains to be determined.

Aged↗
PubMed1994

Autosomal dominant cerebellar ataxia with dementia: evidence for a fourth disease locus.

The autosomal dominant cerebellar ataxias have proved particularly difficult to classify due to the lack of phenotypic concordance both within and between families. Genetic heterogeneity has been established, and disease loci for spinal cerebellar ataxia have been assigned to chromosomes 6 (SCA1), 12 (SCA2) and 14 (Machado Joseph disease (MJD)). Genetic analysis performed on a large Thai kindred with autosomal dominant cerebellar ataxia, in which frontal lobe signs and dementia are commonly observed in affected family members, exclude linkage to the SCA1, SCA2 and MJD loci. This demonstrates that mutation in at least one further locus can cause spinal cerebellar ataxia, indicating the need for caution in the use of markers for predictive testing or prenatal diagnosis these disorders.

Chromosome Mapping↗
PubMed1994

Linkage analysis of 62 X-chromosomal loci excludes the X chromosome in an Icelandic family showing apparent X-linked recessive inheritance of neural tube defects.

We report here the findings of a linkage analysis, involving numerous markers from the human X chromosome, in an attempt to localise a putative gene causing apparent X-linked spina bifida and anencephaly (SBA) in a large Icelandic pedigree. Two-point linkage analysis was performed using markers from 62 informative loci in this family. Although small positive lod scores were found at a number of these loci, none reached the significance level for linkage. Haplotypes were extensively analysed and found to exclude linkage to the X chromosome.

Adult↗
PubMed1994

Genetic linkage to the type VII collagen gene (COL7A1) in 26 families with generalised recessive dystrophic epidermolysis bullosa and anchoring fibril abnormalities.

To strengthen the evidence for genetic linkage to COL7A1, we have studied 26 generalised recessive dystrophic epidermolysis bullosa (EB) families of British, Italian, Irish, and South African origin. We chose two linkage markers, a COL7A1 PvuII intragenic polymorphism and a highly informative anonymous microsatellite marker, D3S1100, which maps close to the COL7A1 locus at 3p21.1-3. Diagnosis was established by family history, clinical examination, immunofluorescence, and ultrastructural studies. The PvuII marker was informative in 16 families with a maximum lod score (Zmax) of 3.51 at recombination fraction (theta) = 0. The D3S1100 microsatellite was informative in 24 out of 25 families with Zmax = 6.8 at theta = 0.05 (Z = 4.94 at theta = 0) and no obligatory recombination events. These data strongly suggest that COL7A1 mutations cause EB in these families and, combined with previous studies, indicate locus homogeneity. The importance of anchoring fibrils for dermal-epidermal adhesion is further underlined. D3S1100 may later prove useful in prenatal diagnosis of this disease, if used in combination with other markers.

Base Sequence↗
PubMed1994

Complex segregation analysis provides evidence for a major gene acting on serum triglyceride levels in 55 British families with familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCHL) was first described as an autosomal dominant inherited trait with primary action on triglyceride levels and secondary effects on cholesterol metabolism. This conclusion has since been questioned by several groups despite subsequent supportive biochemical and metabolic studies. To reexplore the genetics of FCHL, we assembled 55 families from the United Kingdom comprising 559 persons ascertained through probands with both hypercholesterolemia and hypertriglyceridemia. The results of univariate complex segregation analysis were consistent with a major gene acting on triglyceride and explaining two thirds of the genetic variability and 20% of the phenotypic variance in triglyceride levels. Univariate analysis did not identify a major genetic component acting on cholesterol levels. Bivariate segregation analysis rejected a major gene model. We also reexamined the original FCHL pedigrees collected by Goldstein et al and obtained results similar to those in the UK families. The prospects for mapping putative major genes determining triglyceride levels in FCHL patients by linkage analysis are discussed.

Family Health↗
PubMed1993

Genetic recombination events which position the Friedreich ataxia locus proximal to the D9S15/D9S5 linkage group on chromosome 9q.

The absence of recombination between the mutation causing Friedreich ataxia and the two loci which originally assigned the disease locus to chromosome 9 has slowed attempts to isolate and characterize the genetic defect underlying this neurodegenerative disorder. A proximity of less than 1 cM to the linkage group has been proved by the generation of high maximal lod score (Z) to each of the two tightly linked markers D9S15 (Z = 96.69; recombination fraction [theta] = .01) and D9S5 (Z = 98.22; theta = .01). We report here recombination events which indicate that the FRDA locus is located centromeric to the D9S15/D9S5 linkage group, with the most probable order being cen-FRDA-D9S5-D9S15-qter. However, orientation of the markers with respect to the centromere, critical to the positional cloning strategy, remains to be resolved definitively.

Adolescent↗
PubMed1992

Gene targeting for somatic cell manipulation: rapid analysis of reduced chromosome hybrids by Alu-PCR fingerprinting and chromosome painting.

The techniques of reverse genetics rely heavily on parasexual methods for manipulating the human genome. However, the application of somatic cell genetics is severely limited by the availability of suitable endogenous selectable markers in the genome. We have addressed this problem by targeting a universally selectable marker into a predetermined region of the genome, using a stringent selection for homologous recombination. Correct gene targeting to human chromosome 7q11 was screened for by Southern blotting and confirmed by fluorescent in situ hybridization. Reduced chromosome 7 hybrids were generated by chromosome mediated gene transfer and selection for the neo gene. The resultant transgenomes were characterized by a combination of L1 fingerprinting, locus specific marker analysis, Alu-PCR and chromosome 'painting'. Alu-PCR and L1 'fingerprints' are complementary and mutually consistent. Chromosome 'painting' reflects and extends the results obtained for specific marker co-transfer. Thus Alu-PCR 'fingerprinting' and 'painting' combine to rapidly provide an accurate picture of transgenome content and complexity. Gene targeting, chromosome tagging and subsequent isolation can be applied to any region of the genome for which a molecular probe is available.

Animals↗
PubMed1992

Familial recurrence-pattern analysis of cleft lip with or without cleft palate.

Cleft lip with or without cleft palate (CL/P) is a common congenital malformation with an incidence in European white populations of about 1/1,000. The familial clustering of CL/P has been extensively characterized, and epidemiological studies have proposed monogenic models (with reduced penetrance), multifactorial/threshold models, and mixed major-gene/multifactorial models to explain its inheritance. The recognition of an association between two RFLPs at the transforming growth factor alpha (TGFA) locus and CL/P supports a major-gene component to the etiology of CL/P. Risch has shown that the recurrence risk ratio lambda R (risk to relatives, vs. population prevalence) is a useful pointer to the mode of inheritance. Here we further develop the use of lambda R to analyze recurrence-risk data for CL/P. Recurrence risks for first-, second-, and third-degree relatives equate well with oligogenic models with as few as four loci. A monogenic/additive model is strongly rejected. The limited available twin data are also consistent with this model. A "major gene" interacting epistatically with an oligogenic background is shown to be a plausible alternative. Power calculations for a linkage study to map the CL/P major-risk locus suggest that a sample of 50 affected sib pairs will be adequate, but linkage to minor-risk loci will require very much larger samples.

Chromosome Mapping↗