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S T Bennett

Publications and source records attributed to S T Bennett.

At least 19 recordsLinked to original sources
PubMed2005

Cross-calibration of dual-energy X-ray densitometers for a large, multi-center genetic study of osteoporosis.

Osteoporosis is a common disease with a strong genetic component characterized by reduced bone mass and an increased risk of fragility fractures. Bone mineral density (BMD) is the most important determinant of osteoporotic fracture risk, but the genes responsible for BMD regulation and fracture are incompletely defined. To enable multi-center studies to examine the genetic influences on BMD there is a requirement to standardize measurements across different manufacturers of bone densitometers, different versions of machines and different normative ranges. This paper describes a method developed to allow near-identical subjects with low age-adjusted BMD (based on Z-scores) to be recruited in 17 centers using 27 different densitometers. Cross-calibration was based on measurements using a European spine phantom circulated to all centers and measured ten times on each individual machine. From theses values an individual exponential curve, based on nominal versus observed BMD, was derived for each machine. As expected, there were large and significant variations in nominal BMD values, not only between scanners from different manufacturers but also between different versions of scanners from the same manufacturer. Hologic scanners tended to underestimate the nominal BMD, while Lunar scanners overestimated the value. Norland scanners gave mixed values over estimating BMD at the lower nominal value (0.5 g/cm2) while underestimating the value at the higher value (1.5 g/cm2). The validity of the exponential equations was tested using hip and spine measurements on 991 non-proband women from a familial osteoporosis study (FAMOS). After cross-calibration there was a considerable reduction in variation between machines. This observation, coupled with the absence of a similar reduction in variation attributable to a linear regression on age, demonstrated the validity of the cross-calibration approach. Use of the cross-calibration curves along with a standard normative range (in the case of this study, the Hologic normative range) allowed age-specific Z-scores to be used as an inclusion criterion in this genetic study, a method that will be useful for other trials where age-specific BMD inclusion criteria are required.

Absorptiometry, Photon↗
PubMed2001

Genomewide search in familial Paget disease of bone shows evidence of genetic heterogeneity with candidate loci on chromosomes 2q36, 10p13, and 5q35.

Paget disease of bone (PDB) is a common disorder characterized by focal abnormalities of increased and disorganized bone turnover. Genetic factors are important in the pathogenesis of PDB, and previous studies have shown that the PDB-like bone dysplasia familial expansile osteolysis is caused by activating mutations in the TNFRSF11A gene that encodes receptor activator of nuclear factor kappa B (RANK); however, linkage studies, coupled with mutation screening, have excluded involvement of RANK in the vast majority of patients with PDB. To identify other candidate loci for PDB, we conducted a genomewide search in 319 individuals, from 62 kindreds with familial PDB, who were predominantly of British descent. The pattern of inheritance in the study group as a whole was consistent with autosomal dominant transmission of the disease. Parametric multipoint linkage analysis, under a model of heterogeneity, identified three chromosomal regions with LOD scores above the threshold for suggestive linkage. These were on chromosomes 2q36 (LOD score 2.7 at 218.24 cM), 5q35 (LOD score 3.0 at 189.63 cM), and 10p13 (LOD score 2.6 at 41.43 cM). For each of these loci, formal heterogeneity testing with HOMOG supported a model of linkage with heterogeneity, as opposed to no linkage or linkage with homogeneity. Two-point linkage analysis with a series of markers from the 5q35 region in another large kindred with autosomal dominant familial PDB also supported linkage to the candidate region with a maximum LOD score of 3.47 at D5S2034 (187.8 cM). These data indicate the presence of several susceptibility loci for PDB and identify a strong candidate locus for the disease, on chromosome 5q35.

Chromosome Mapping↗
PubMed2001

Toward developing a genome-wide microsatellite marker set for linkage analysis in the rhesus macaque (Macaca mulatta): identification of 76 polymorphic markers.

Linkage analysis can be problematic in humans because of the lack of large, multigenerational pedigrees and the difficulties in obtaining phenotypic data on all family members. In contrast, large, captive colonies of rhesus macaque are a potentially valuable resource for linkage studies because detailed phenotypic and genealogical data are kept, inbreeding is avoided, and DNA samples can usually be obtained. Microsatellite marker sets for genome-wide screening are available in a number of species, but not for the rhesus macaque. We tested primers to 400 human microsatellite markers from a genome-wide mapping set using DNA from nine unrelated female rhesus macaques. We found that 76 (19%) of the primers amplified a polymorphic product using the standard protocols for human DNA. The average heterozygosity of the markers in humans was 0.80, compared to 0.65 in the rhesus macaques. This study provides preliminary data, which could be used toward the development of a linkage mapping set in this species. There would be a need, however, to confirm the Mendelian inheritance of the markers.

Animals↗
PubMed2001

Evidence that insulin is imprinted in the human yolk sac.

Allelic variation in the size of the insulin (INS) variable number tandem repeat (VNTR) correlates with the expression of both INS in the pancreas and thymus and IGF2 (the gene downstream of INS) in the placenta. In addition, the shorter, class I alleles are associated with type 1 diabetes, whereas the longer, class III alleles are associated with type 2 diabetes, polycystic ovary syndrome (PCOS), and size at birth. Parent-of-origin effects have been reported for type 2 diabetes and PCOS, thus implicating a role for genomic imprinting in these phenotypes. In mice, Ins2 is imprinted and paternally expressed in the yolk sac. In humans, evidence for the imprinting of INS is circumstantial, with occasional monoallelic expression in the thymus. In the present study, we found evidence for the imprinted paternal expression of INS in the human yolk sac. Two other imprinted genes from the same cluster are also expressed monoallelically in the human yolk sac. IGF2 was expressed solely from the paternal allele, and H19 was expressed solely from the maternal allele. These data suggest not only further functional roles for the human yolk sac in early fetal growth, but also evidence for a potential causal link between the control of insulin expression during development and insulin/growth-related diseases in later life.

Alleles↗
PubMed2000

Evidence for a major gene for bone mineral density in idiopathic osteoporotic families.

Although there have been a number of studies indicating a heritable component for osteoporosis in middle to late adulthood, the etiology of osteoporosis in young people is uncertain. The present study aims to evaluate the extent to which genetic factors influence familial resemblance for bone mineral density (BMD) in families ascertained on the basis of young osteoporotic probands. The sample comprises eight families (74 total individuals) that were identified through a proband under the age of 35 years with a history of two or more fractures and a spinal bone density of at least 2.5 SDs below the mean for age and sex (Z score). Secondary causes of osteoporosis were excluded in the probands. In total, 27% (18/66) of the probands' relatives had osteoporosis and an additional 30% (20/66) had osteopenia. Classical segregation analysis was performed to evaluate the extent to which a genetic etiology could account for familial resemblance in these families. The results indicate a major gene of codominant inheritance for spinal BMD. Model-fitting comparisons revealed no support for environmental effects or for polygenic inheritance.

Adolescent↗
PubMed1999

INS VNTR allelic variation and dynamic insulin secretion in healthy adult non-diabetic Caucasian subjects.

AIMS: To elucidate the relationship between the human insulin gene INS VNTR regulatory polymorphism and insulin secretion. The polymorphism arises from tandem repetition of 14-15 bp oligonucleotides. In Caucasians, repeat number varies from 26 to over 200, with two main and discrete allele size classes: class I (26-63 repeats) and class III (141-209 repeats). Class I allele homozygosity is associated with elevated risk of developing Type 1 diabetes, while the class III allele has been associated with increased risk of Type 2 diabetes, polycystic ovary syndrome (PCOS) and with larger size at birth, which may influence development of adult disease. METHODS: Thirty-one healthy adult subjects with normal glucose tolerance, underwent an intravenous glucose tolerance test with one minute sampling. Seventeen subjects were homozygous for class I alleles (14 excluding individuals carrying alleles associated with parent-of-origin effects and heterogeneity in allele transmission) and 14 homozygous for class III alleles. The groups were well matched. RESULTS: No significant differences in amount or rate of insulin secretion, or beta cell function were detected between the two groups. There was a difference in pattern of pulsatile insulin secretion with more 9-minute oscillations in class I homozygotes (P<0.026). The after-load glucose concentration was also higher in subjects with class I alleles (P<0.03). CONCLUSIONS: These results warrant further analysis of possible association between allelic variation of the INS VNTR and the pulsatility of insulin secretion.

Adult↗
PubMed1998

Association of the INS VNTR with size at birth. ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood.

Size at birth is an important determinant of perinatal survival and has also been associated with the risk for cardiovascular disease and type 2 diabetes in adult life. Common genetic variation that regulates fetal growth could therefore influence perinatal survival and predispose to the development of adult disease. We have tested the insulin gene (INS) variable number of tandem repeats (VNTR) locus, which in Caucasians has two main allele sizes (class I and class III; ref. 3), as a functional candidate polymorphism for association with size at birth, as it has been shown to influence transcription of INS (refs 3-5). In a cohort of 758 term singletons (Avon Longitudinal Study of Pregnancy and Childhood; ALSPAC) followed longitudinally from birth to 2 years, we detected significant genetic associations with size at birth: class III homozygotes had larger mean head circumference (P=0.004) than class I homozygotes. These associations were amplified in babies who did not show postnatal realignment of growth (45%), and were also evident for length (P=0.015) and weight (P=0.009) at birth. The INS VNTR III/II genotype might have bestowed a perinatal survival during human history by conferring larger size at birth. Common genetic variation of this kind may contribute to reported associations between birth size and adult disease.

Birth Weight↗
PubMed1998

Divergence between genetic determinants of IGF2 transcription levels in leukocytes and of IDDM2-encoded susceptibility to type 1 diabetes.

The IDDM2 susceptibility locus in type 1 diabetes corresponds to a variable number of tandem repeats (VNTR) upstream of the insulin (INS) and insulin-like growth factor 2 (IGF2) genes. Large VNTR alleles (class III) are dominantly protective, whereas small alleles (class I) are predisposing. IGF2 has been considered a prime candidate for mediating IDDM2-encoded susceptibility because of its proximity to the VNTR, mitogenic properties and parental effects at IDDM2 suggest the involvement of an imprinted gene. IGF2 is imprinted with exclusive expression of the paternal gene. However, there is polymorphic relaxation of IGF2 imprinting in leukocytes. VNTR allelic variation affecting either the extent of relaxation or transcription independent of parental origin might explain the IDDM2 effect. To test this, we compared IGF2 expression between chromosomes with a class III or I allele in leukocytes and stimulated lymphocytes. No significant difference was detected between the two classes. Furthermore, the (+) allele of an ApaI polymorphism in the 3'-untranslated region of IGF2 was associated with significantly higher IGF2 messenger ribonucleic acid levels than the (-) allele, but was not associated with type 1 diabetes. The absence of transcriptional effects in leukocytes on IGF2 by the VNTR, which is the disease-predisposing locus, and the presence of a strong association between IGF2 levels and ApaI, which is not associated with the disease, argue against IGF2 expression in leukocytes as the mediator of IDDM2-encoded susceptibility. Taken together, these results support studies suggesting that INS expression in the thymus is a primary target of the IDDM2 susceptibility locus.

Alleles↗
PubMed1997

Linkage and association of insulin gene VNTR regulatory polymorphism with polycystic ovary syndrome.

BACKGROUND: Polycystic ovary syndrome (PCOS) is a common endocrine disorder affecting up to 10% of women of reproductive age. Women with anovulatory PCOS have hyperinsulinaemia, insulin resistance, and dyslipidaemia, and the syndrome is associated with greatly increased risks of non-insulin-dependent diabetes mellitus and cardiovascular disease and it often clusters in families. The VNTR (variable number of tandem repeats) locus upstream of the insulin gene (INS) regulates insulin expression. We have studied INS VNTR as a candidate genetic locus for susceptibility to PCOS. METHODS: We evaluated linkage of PCOS to the INS VNTR locus on chromosome 11p15.5 in 17 families with several cases, and looked for an association between VNTR and PCOS in two additional clinic populations. VNTR genotypes were designated I/I, I/III, and III/III and linkage disequilibrium mapping was used to test the primary role of the VNTR. FINDINGS: In a group of PCOS/male pattern baldness families, we obtained positive evidence for linkage to 11p15.5 (p = 0.002). The INS VNTR III/III genotype was associated with an increased risk of PCOS in two independent case-control studies (odds ratios 8.20 [p = 0.005] and 5.70 [p = 0.043]). Multilocus linkage disequilibrium mapping suggests that VNTR itself is the predisposing locus. INTERPRETATION: Mapping of susceptibility to PCOS to the INS VNTR implies that PCOS is due, in part, to an inherited alteration in insulin production. The data suggest a mechanistic link between type 2 diabetes and PCOS, which is a risk factor for diabetes later in life.

Alleles↗
PubMed1997

Insulin expression in human thymus is modulated by INS VNTR alleles at the IDDM2 locus.

Type 1 diabetes or insulin-dependent diabetes mellitus (IDDM) is due to autoimmune destruction of pancreatic beta-cells. Genetic susceptibility to IDDM is encoded by several loci, one of which (IDDM2) maps to a variable number of tandem repeats (VNTR) minisatellite, upstream of the insulin gene (INS). The short class I VNTR alleles (26-63 repeats) predispose to IDDM, while class III alleles (140-210 repeats) have a dominant protective effect. We have reported that, in human adult and fetal pancreas in vivo, class III alleles are associated with marginally lower INS mRNA levels than class I, suggesting transcriptional effects of the VNTR. These may be related to type 1 diabetes pathogenesis, as insulin is the only known beta-cell specific IDDM autoantigen. In search of a more plausible mechanism for the dominant effect of class III alleles, we analysed expression of insulin in human fetal thymus, a critical site for tolerance induction to self proteins. Insulin was detected in all thymus tissues examined and class III VNTR alleles were associated with 2- to 3-fold higher INS mRNA levels than class I. We therefore propose higher levels of thymic INS expression, facilitating immune tolerance induction, as a mechanism for the dominant protective effect of class III alleles.

Abortion, Therapeutic↗
PubMed1997

The insulin gene is transcribed in the human thymus and transcription levels correlated with allelic variation at the INS VNTR-IDDM2 susceptibility locus for type 1 diabetes.

Type 1, or insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease associated with loss of tolerance to several pancreatic islet cell molecules, including insulin, glutamic acid decarboxylase (GAD), ICA69 and the tyrosine phosphatase IA-2 (refs 1-3). Among several predisposing loci, IDDM2 maps to the insulin gene (INS) VNTR (variable number of tandem repeats) minisatellite on chromosome 11p15 (refs 4-9). Allelic variation at this VNTR locus correlates with steady-state levels of INS mRNA in pancreas and transfected rodent cell lines, but it is difficult to reconcile the association of lower INS mRNA levels in the pancreas with class III VNTRs that are dominantly protective from IDDM. We show that during fetal development and childhood, mRNAs for insulin and other islet cell autoantigens (GAD, ICA69, IA-2) are expressed at low levels in the human thymus. Critically, we also detect proinsulin and insulin protein. VNTR alleles correlate with differential INS mRNA expression in the thymus where, in contrast to the pancreas, protective class III VNTRs are associated with higher steady-state levels of INS mRNA expression. This finding provides a plausible explanation for the dominant protective effect of class III VNTRs, and suggests that diabetes susceptibility and resistance associated with IDDM2 may derive from the VNTR influence on INS transcription in the thymus. Higher levels of (pro)insulin in the thymus may promote negative selection (deletion) of insulin-specific T-lymphocytes which play a critical role in the pathogenesis of type-1 diabetes.

Aging↗
PubMed1997

Insulin VNTR allele-specific effect in type 1 diabetes depends on identity of untransmitted paternal allele. The IMDIAB Group.

The IDDM2 type 1 diabetes susceptibility locus was mapped to and identified as allelic variation at the insulin gene (INS) VNTR regulatory polymorphism. In Caucasians, INS VNTR alleles divide into two discrete size classes. Class I alleles (26 to 63 repeats) predispose in a recessive way to type 1 diabetes, while class III alleles (140 to more than 200 repeats) are dominantly protective. The protective effect may be explained by higher levels of class III VNTR-associated INS mRNA in thymus such that elevated levels of preproinsulin protein enhance immune tolerance to preproinsulin, a key autoantigen in type 1 diabetes pathogenesis. The mode of action of IDDM2 is complicated, however, by parent-of-origin effects and possible allelic heterogeneity within the two defined allele classes. We have now analysed transmission of specific VNTR alleles in 1,316 families and demonstrate that a particular class I allele does not predispose to disease when paternally inherited, suggestive of polymorphic imprinting. But this paternal effect is observed only when the father's untransmitted allele is a class III. This allelic interaction is reminiscent of epigenetic phenomena observed in plants (for example, paramutation; ref. 17) and in yeast (for example, trans-inactivation; ref. 18). If untransmitted chromosomes can have functional effects on the biological properties of transmitted chromosomes, the implications for human genetics and disease are potentially considerable.

Alleles↗
PubMed1996

Imprinted and genotype-specific expression of genes at the IDDM2 locus in pancreas and leucocytes.

One of the loci encoding susceptibility to insulin-dependent diabetes mellitus (IDDM) is IDDM2, mapped to a variable number of tandem repeats (VNTR) polymorphism situated 596 bp upstream of the insulin gene (INS). The shorter alleles (class I) predispose to IDDM, while the longer class III alleles are protective. Besides INS, it is possible that transcription levels of IGF2, the nearby gene encoding the insulin-like growth factor II, may be modulated by allelic forms of the VNTR. In an effort to define the pathophysiologic mechanism of the IDDM2 effect, we examined the effect, in cis, of VNTR genotype on steady-state mRNA levels of INS in samples of human fetal pancreas, and of IGF2 in leucocytes of diabetic children. Relative levels of mRNA transcripts derived from each chromosome carrying a defined VNTR allele were measured by RT-PCR, taking advantage of transcribed polymorphisms at the 3' untranslated region of each gene. In 10 samples of human fetal pancreas, INS transcripts from chromosomes carrying a class III VNTR were slightly but significantly (P = 0.015) lower than those from class I (13% lower, 95% confidence limits 3-21%). In 10 leucocyte samples, mRNA from both IGF2 alleles was seen, indicating relaxation of the parental imprinting of IGF2 in these cells. However, this relaxation was incomplete as maternal allele mRNA was systematically at a lower level than paternal. The paternal/maternal ratio varied widely among individual subjects. Two of the most extreme cases, demonstrating almost complete repression of the maternal allele, were identical twins, suggesting that this variable relaxation of imprinting is genotype-dependent. However, this genotype-dependence cannot be accounted for by the maternal VNTR, as the mean ratios of paternal/maternal IGF2 mRNA levels were not statistically different in individuals with a maternal VNTR of class I vs. class III (3.2 +/- 1.5 vs. 3.89 +/- 0.94). Thus, we present evidence that: (a) class III VNTR alleles are associated with lower INS mRNA in fetal pancreas than class I alleles. The biologic importance of this difference remains to be determined; and (b) the variable relaxation of IGF2 imprinting seen in human leucocytes is not dependent on the presence of a class I vs. a class III VNTR.

Alleles↗
PubMed1996

IDDM2-VNTR-encoded susceptibility to type 1 diabetes: dominant protection and parental transmission of alleles of the insulin gene-linked minisatellite locus.

IDDM2-encoded predisposition to type 1 diabetes has recently been mapped to the minisatellite or variable number of tandem repeat (VNTR) locus upstream of the insulin and insulin-like growth factor II genes on human chromosome 11p15.5. In a UK case-control study (n = 228 sporadic diabetics; n = 441 healthy controls), we show here that the genotype homozygous for VNTR class I alleles is predisposing to disease (RR = 2.68), and VNTR class III alleles are dominantly protective (RR = 0.37). In 722 diabetic families from the UK (n = 356), USA (n = 173), Denmark (n = 55) and Sardinia (n = 138), we have analysed the transmission of class I alleles to diabetic offspring from class I/III heterozygous parents. We confirm that in families from the USA, class I alleles are transmitted preferentially from fathers. However, in family data sets from the UK, Denmark and Sardinia, the reverse is true and maternal transmission is stronger. Furthermore, in the UK family data set, the difference between maternal and paternal transmissions is significant (P < 0.05). It is therefore unlikely that 'maternal imprinting' alone explains the parent-of-origin effects in IDDM2-encoded predisposition to type 1 diabetes, at least not in the UK. There is a relationship between VNTR class (allele length) and insulin gene expression, though some results from different studies are conflicting. In the human adult cadaveric pancreas, we confirm our preliminary results that class III alleles are associated with lower levels of insulin mRNA in vivo. Similar results have been obtained independently in human foetal pancreas samples. It is difficult to explain how these marginally lower levels of insulin expression could account for the observed VNTR class III-encoded protective effect. Perhaps the site of action of IDDM2, mediated by VNTR allelic variation, is not the pancreas but some other organ such as the thymus.

Adolescent↗