Factor V Leiden is associated with pre-eclampsia but not with fetal growth restriction: a genetic association study and meta-analysis.

BACKGROUND: Adverse pregnancy outcomes have been related to environmental and/or genetic factors. Of interest are genes associated with the clotting system as any perturbation in the balance of thrombotic and thrombolytic cascades could affect the placental circulation and hence the viability of the developing fetus. Several previous reports using relatively small numbers of cases and controls have suggested that there is a relationship between poor pregnancy outcomes and two polymorphisms, one in the factor V gene, the 1691G to A change (rs6025) located on chromosome 1q23 (factor V Leiden, FVL), and the other in the prothrombin gene, 20210G to A change (rs1799963) on chromosome 11p11-q12 (PT). These results, however, are conflicting. METHODS: We genotyped 6755 mother/infant pairs from the Avon Longitudinal Study of Parents and Children (ALSPAC) to determine whether maternal or fetal FVL or PT, either alone or in combination, are associated with fetal growth restriction (FGR) or pre-eclampsia (PE). We also added the present results to previous cohort studies using meta-analysis. RESULTS: Smoking, primiparity and lower body mass index (BMI) were all associated with FGR, but neither maternal nor fetal FVL or PT, singly or in combination, were associated with FGR in the ALSPAC cohort. Meta-analysis confirmed the lack of association between maternal FVL and FGR with a pooled odds ratio (OR) of 1.15 [95% confidence interval (CI) 0.95-1.39]. High BMI, primiparity, diabetes and chronic hypertension were all associated with pre-eclampsia. Combining ALSPAC results with previous studies in ameta-analysis indicated that maternal FVL is significantly associated with pre-eclampsia, with a pooled OR of 1.49 (95% CI 1.13-1.96). CONCLUSION: Neither maternal nor fetal FVL or PT, singly or in combination, are associated with FGR; this contradicts previous case-control studies and meta-analyses based on these studies. In a meta-analysis of all published cohort studies to date, maternal FVL appears to increase the risk of pre-eclampsia by almost 50%. This result is robust, homogeneous and does not appear to be affected by publication bias.

An investigation of FRAXA intermediate allele phenotype in a longitudinal sample.

The FRAXA trinucleotide repeat at Xq27.3 gives rise to fragile X syndrome when fully expanded, and both premature ovarian failure (POF) and fragile X tremor and ataxia syndrome (FXTAS) when in the premutation range. Reports of phenotypic effects extending into the intermediate repeat range are inconsistent but some studies suggest that these smaller expansions predispose to special educational needs (SEN). This study utilises the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort to investigate cognitive and behavioural variables that might be associated with FRAXA intermediate alleles. The current study failed to find any strong evidence of association of FRAXA intermediate alleles with SEN, behavioural problems or cognitive difficulties. However, our findings illustrate some of the difficulties encountered in identifying individuals with SEN. The power to identify specific components of cognitive and behavioural difficulties was reduced due to elective drop-out, which is characteristic of longitudinal studies. Our findings demonstrate the non-random loss of participants from this cohort and highlight problems that may arise when such data are used in genetic association studies.

An interaction between the IL-4Ralpha gene and infection is associated with atopic eczema in young children.

BACKGROUND: A gain of function mutation (Q551- > R) in the IL-4 receptor alpha-chain (IL-4Ralpha) has been found to be associated with atopy in some studies but not others. The different results may be explained by interactions between the IL-4Ralpha polymorphism and environmental factors. OBJECTIVES: To identify interactions between the R551 mutation and environmental factors that are associated with atopy. METHODS: DNA from the Children in Focus (CiF) cohort of the Avon Longitudinal Study of Parents and Children (ALSPAC) was genotyped by heteroduplex formation for the presence of the R551 polymorphism. The data were then analysed for associations with flexural eczema as an indicator of atopic eczema, skin prick tests to allergens and serum IgE levels, and for interactions with environmental factors. RESULTS: A significant (P = 0.02) positive association was seen between the R551 polymorphism and flexural eczema in children up to 6 months of age who had not been given antibiotics, but not in children who had been given antibiotics. This association was maintained as a trend until 30 to 42 months of age but was no longer statistically significant. There was no significant association between the R551 polymorphism and positive skin prick tests or levels of serum IgE at 61 months of age, consistent with the effect of the R551 polymorphism being restricted to early life. CONCLUSION: There is an association between the R551 polymorphism and flexural eczema in children at 6 months of age who have not had infection requiring treatment with antibiotics. Restriction of the R551 association with eczema to children who have not had antibiotics lends support to the 'hygiene hypothesis', which states that exposure to infection in childhood can protect against allergic disease.

Hyperphagic short stature and Prader--Willi syndrome: a comparison of behavioural phenotypes, genotypes and indices of stress.

BACKGROUND: The clinical features of hyperphagic short stature (HSS) include short stature secondary to growth hormone insufficiency, excessive appetite (hyperphagia) and mild learning disabilities. Affected children characteristically live in conditions of high psychosocial stress. Symptoms resolve when the child is removed from the stressful environment. Family studies indicate a genetic predisposition. AIMS: To compare the behavioural and stress profiles of HSS with those of Prader--Willi syndrome (PWS), and to test the hypothesis that the genetic locus that predisposes to HSS co-inherits with the PWS locus at 15q11--13. METHOD: Twenty-five children with HSS, mean age 9.1 (s.d. 3.8) years, 28% female, were compared with 30 children with PWS, mean age 8.8 (s.d. 2.8) years, 33% female. RESULTS: The clinical profiles were largely similar across the conditions, but no evidence was found in HSS of co-inheritance of the PWS critical region. CONCLUSIONS: Hyperphagic short stature is one of the very few behavioural diseases associated with a pathognomonic physiological abnormality. Investigations of the suggested genetic dysregulation, which is so sensitive to environmental influences, may well be of importance in a broader context.

Disruption of the bipartite imprinting center in a family with Angelman syndrome.

Imprinting in 15q11-q13 is controlled by a bipartite imprinting center (IC), which maps to the SNURF-SNRPN locus. Deletions of the exon 1 region impair the establishment or maintenance of the paternal imprint and can cause Prader-Willi syndrome (PWS). Deletions of a region 35 kb upstream of exon 1 impair maternal imprinting and can cause Angelman syndrome (AS). So far, in all affected sibs with an imprinting defect, an inherited IC deletion was identified. We report on two sibs with AS who do not have an IC deletion but instead have a 1-1.5 Mb inversion separating the two IC elements. The inversion is transmitted silently through the male germline but impairs maternal imprinting after transmission through the female germline. Our findings suggest that the close proximity and/or the correct orientation of the two IC elements are/is necessary for the establishment of a maternal imprint.

The association of aneuploidy and mild fetal pyelectasis in an unselected population: the results of a multicenter study.

INTRODUCTION: Mild pyelectasis is a common finding and there is some debate as to its association with aneuploidy. The results of a large, prospective, multicenter study of mild pyelectasis designed to determine the incidence and association with aneuploidy in an unselected population are reported. METHODS: A large multicenter, prospective observational study of unselected fetuses with mild pyelectasis identified between 16 and 26 weeks' gestation in routine ultrasound departments. RESULTS: There were 737 fetuses with mild pyelectasis of which 12 had an abnormal karyotype. Pyelectasis was isolated in three fetuses with Down syndrome, but in one the mother was older (36 years). CONCLUSION: These data confirm the fact that the presence of mild fetal pyelectasis increases the risk for aneuploidy, in particular trisomy 21. However, other risk factors should be considered before embarking on fetal karyotyping, as for most pregnancies complicated by isolated mild pyelectasis, risks of aneuploidy will remain small.

An assessment of screening strategies for fragile X syndrome in the UK.

BACKGROUND: Fragile X syndrome is an inherited form of learning disability that was defined in the late 1970s by cytogenetic detection of an associated fragile site on the X chromosome (Xq27.3). Cytogenetic estimates of the prevalence of fragile X syndrome were as high as 1 in 1039 males but have since been revised downwards. Fragile X syndrome is associated with few medical problems and the subtle physical features make clinical diagnosis difficult. The unusual pattern of inheritance, delineated in the 1980s, was explained once the fragile X syndrome gene (FMR1) had been identified in 1991. This gene contains a highly variable repeat of the nucleotide triplet, cytosine-guanine-guanine (CGG). Fragile X syndrome is caused by a large expansion of this CGG repeat (full mutation) that leads to silencing of the FMR1 gene so no gene product (FMRP) is made. This is the ultimate cause of the learning disability that, in males, is sufficient to preclude independent living. Family studies show that all individuals with a full mutation inherit it from a female (usually unaffected) who carries either a full mutation or a premutation, a smaller repeat expansion (approximately 55-200 repeats) that is unstable on female transmission. The chance of a premutation expanding to a full mutation is positively associated with the size of the repeat (approximately 95% by 90 repeats) but only for female transmissions. When a man transmits a premutation, it remains a premutation; his children are, therefore, unaffected by overt learning difficulties. The potential for population screening or systematic case-finding and extended family testing exists because every unaffected mother of an affected child has a detectable CGG repeat expansion. Reliable prenatal diagnosis is possible in males. OBJECTIVES: To assess the feasibility and acceptability of population screening by addressing the following questions in the context of existing services for families with fragile X syndrome. (1) Is there a suitable test for all fragile X genotypes? (2) What are the UK population distribution of FMR1 repeat sizes, and the prevalence of full and premutations in both sexes? (3) What reliable information, in terms of the chance of an affected child, is available to women with premutations between 55 and 200 repeats? (4) What is the effect of a premutation on the person who carries it? (5) What information is available to women with intermediate alleles of 41 to 54-60 repeats? (6) How many affected people are diagnosed? (7) Given the practice of offering extended family testing (cascade testing), what is the population prevalence of 'as-yet-undiagnosed' female carriers of a full or premutation? What proportion of women at risk can be reached by cascade testing? (8) What are the costs of fragile X syndrome to an affected person and their family and to the NHS and society? (9) What is the attitude of families to the benefits and costs of a diagnosis of fragile X syndrome, and to the prospect of population screening? (10) What data are available from existing population screening programmes? (11) What alternatives to population screening exist and are these feasible? METHODS: A key aspect of the review process was to assemble a team with extensive first-hand experience of all aspects of fragile X syndrome, including affected families and the services they use, and a wide knowledge of the relevant literature. They had followed the critical discussions at all the biennial international workshops on fragile X syndrome, including a special session at the 7th International Workshop in 1995 at which an earlier (and substantially different) draft of this report was discussed. The biomedical literature review of 2429 papers was based on MEDLINE searches, extending to PsycINFO and BIDS for the psychological aspects of [fragile X syndrome] screening. Questionnaire-based information was obtained from the UK Fragile X Society and data were collected directly from all the regional clinical genetics centres in 1995 and 1998. RESULTS: Unlike cytogenetic approaches, DNA analysis can reliably determine the FMR1 CGG repeat number and detect full mutations; however, a combination of polymerase chain reaction and Southern blotting tests is required, which limits high throughput. There are UK population-based data on FMR1 repeat sizes of up to 60 repeats but insufficient to provide a reliable estimate of the prevalence of premutations (approximately 60-200 repeats). The few data and estimates in the literature of women carriers of the premutation range from 1 in 246 to 1 in 550. Two UK DNA-based estimates of the prevalence of males with the full mutation are 1 in 4090 (Coventry) and 1 in 5530 (Wessex). There are reasonable family-based data for the risk of expansion to a full mutation for the larger premutations but in the 50-69 repeat range the estimates are less secure. (ABSTRACT TRUNCATED)

ALSPAC--the Avon Longitudinal Study of Parents and Children. I. Study methodology.

ALSPAC (The Avon Longitudinal Study of Parents and Children, formerly the Avon Longitudinal Study of Pregnancy and Childhood) was specifically designed to determine ways in which the individual's genotype combines with environmental pressures to influence health and development. To date, there are comprehensive data on approximately 10,000 children and their parents, from early pregnancy until the children are aged between 8 and 9. The study aims to continue to collect detailed data on the children as they go through puberty noting, in particular, changes in anthropometry, attitudes and behaviour, fitness and other cardiovascular risk factors, bone mineralisation, allergic symptoms and mental health. The study started early during pregnancy and collected very detailed data from the mother and her partner before the child was born. This not only provided accurate data on concurrent features, especially medication, symptoms, diet and lifestyle, attitudes and behaviour, social and environmental features, but was unbiased by parental knowledge of any problems that the child might develop. From the time of the child's birth many different aspects of the child's environment have been monitored and a wide range of phenotypic data collected. By virtue of being based in one geographic area, linkage to medical and educational records is relatively simple, and hands-on assessments of children and parents using local facilities has the advantage of high quality control. The comprehensiveness of the ALSPAC approach with a total population sample unselected by disease status, and the availability of parental genotypes, provides an adequate sample for statistical analysis and for avoiding spurious results. The study has an open policy in regard to collaboration within strict confidentiality rules.

Mapping of X chromosome inversion breakpoints [inv(X)(q11q28)] associated with FG syndrome: a second FG locus [FGS2]?

FG syndrome is an X-linked condition comprising mental retardation, congenital hypotonia, macrocephaly, distinctive facial changes, and constipation or anal malformations. In a linkage analysis, we mapped a major FG syndrome locus [FGS1] to Xq13, between loci DXS135 and DXS1066. The same data, however, clearly demonstrated genetic heterogeneity. Recently, we studied a French family in which an inversion [inv(X)(q12q28)] segregates with clinical symptoms of FG syndrome. This suggests that one of the breakpoints corresponds to a second FG syndrome locus [FGS2]. We report the results of fluorescence in situ hybridization analysis performed in this family using YACs and cosmids encompassing the Xq11q12 and Xq28 regions. Two YACs, one positive for the DXS1 locus at Xq11.2 and one positive for the color vision pigment genes and G6PD loci at Xq28, were found to cross the breakpoints, respectively. We postulate that a gene might be disrupted by one of the breakpoints.

A new human genetic resource: a DNA bank established as part of the Avon longitudinal study of pregnancy and childhood (ALSPAC).

We describe a unique human DNA resource forming part of the Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC), a longitudinal cohort study involving 14 000 children and their families living in a geographically defined area of England. The DNA bank will underpin the search for associations between genetic polymorphisms and common health outcomes. The opportunities to collect blood samples suitable for DNA extraction are necessarily limited, and the samples themselves have often been treated in different ways and have varied storage histories. With the need to maximise yields, the choice of DNA extraction method is critical to the success of the bank and we have investigated the suitability of various commercial and in-house methods of DNA extraction. Various steps have been taken to minimise errors in sample address and identification, including the use of a pipetting robot for dilution and transfer of samples between 96-well arrays to provide aliquots suitable for PCR. The robot has been programmed to cope with concentrated viscous DNA solutions.

Mutational spectrum in the cardioauditory syndrome of Jervell and Lange-Nielsen.

Jervell and Lange-Nielsen syndrome (JLNS) is an autosomal recessive syndrome characterised by profound congenital sensorineural deafness and prolongation of the QT interval on the electrocardiogram, representing abnormal ventricular repolarisation. In a study of ten British and Norwegian families with JLNS, we have identified all of the mutations in the KCNQ1 gene, including two that are novel. Of the nine mutations identified in this group of 10 families, five are nonsense or frameshift mutations. Truncation of the protein proximal to the recently identified C-terminal assembly domain is expected to preclude assembly of KCNQ1 monomers into tetramers and explains the recessive inheritance of JLNS. However, study of a frameshift mutation, with a dominant effect phenotypically, suggests the presence of another assembly domain nearer to the N-terminus.

Diagnosis of fragile-X syndrome: the experiences of parents.

In order to assess some aspects of the quality of care for families seeking the cause of their child(ren)s intellectual disability, a postal questionnaire was sent to parents of children with fragile-X syndrome, who were members of the UK Fragile-X Society. Although the interval taken to get a diagnosis ('lagtime') has fallen over time, other aspects of care could still be improved. Most families feel that having a diagnosis is an advantage, but many still find the diagnostic process distressing and feel unsupported. Not all families are referred for genetic counselling, and even those who are do not always understand or retain the information given. Most families feel that having a diagnosis is a benefit rather than a disadvantage.

Neural basis of an inherited speech and language disorder.

Investigation of the three-generation KE family, half of whose members are affected by a pronounced verbal dyspraxia, has led to identification of their core deficit as one involving sequential articulation and orofacial praxis. A positron emission tomography activation study revealed functional abnormalities in both cortical and subcortical motor-related areas of the frontal lobe, while quantitative analyses of magnetic resonance imaging scans revealed structural abnormalities in several of these same areas, particularly the caudate nucleus, which was found to be abnormally small bilaterally. A recent linkage study [Fisher, S., Vargha-Khadem, F., Watkins, K. E., Monaco, A. P. & Pembry, M. E. (1998) Nat. Genet. 18, 168-170] localized the abnormal gene (SPCH1) to a 5. 6-centiMorgan interval in the chromosomal band 7q31. The genetic mutation or deletion in this region has resulted in the abnormal development of several brain areas that appear to be critical for both orofacial movements and sequential articulation, leading to marked disruption of speech and expressive language.

Recurrence risks in offspring of adults with major heart defects: results from first cohort of British collaborative study.

BACKGROUND: Congenital heart defects are generally assumed to have a multifactorial aetiology. We have tested this hypothesis by studying adults with heart defects and their families. METHODS: We identified 1094 patients who survived surgery for major cardiac defects before 1970. We chose individuals with disturbance of situs or segmental connection, with atrioventricular septal defect or with tetralogy of Fallot. After exclusion and non-participation, 727 individuals were traced. Each was visited by an investigator and completed a detailed questionnaire. If possible, all "normal" offspring were examined by a paediatric cardiologist. FINDINGS: The 727 individuals had 393 live offspring. There were 71 miscarriages and five terminated pregnancies. Overall, we found recurrent heart defects in 16 liveborn offspring--a recurrence risk of 4.1%. This result differed significantly from sibling risk (2.1%; p=0.021). More congenital heart defects occurred in the offspring of affected women than in those of affected men (p=0.047); when all malformations (cardiac and non-cardiac) in the offspring were taken into account the excess was more significant (p=0.032). We found an excess of miscarriages in the offspring of affected women (p=0.001). In tetralogy of Fallot, heart defects occurred in seven (3.1%) of 223 offspring, 12 (2.2%) of 539 siblings, five (0.3%) of 1575 second-degree relatives, and eight (0.3%) of 2728 third-degree relatives. INTERPRETATION: Our findings do not support a polygenic basis for all heart defects. Atrioventricular septal defect seems to be a single-gene defect and tetralogy of Fallot a polygenic disorder with a small number of interacting genes. Our data suggest that isolated transposition of the great arteries is a sporadic defect.

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.

Radiological malformations of the ear in Pendred syndrome.

Pendred syndrome comprises the association of severe congenital sensorineural deafness with thyroid pathology. Although it is the commonest form of syndromic hearing loss, the primary genetic defect remains unknown. The variable clinical presentation allied to the difficulty in securing the diagnosis have resulted in relatively poor documentation of the radiological features of this syndrome. We now present data on 40 patients, all complying with strict diagnostic criteria for the disorder, and describe our experience of the prevalence of specific malformations of the inner ear as well as comparing the relative merits of computed tomography (CT) and magnetic resonance imaging (MRI) in the investigation of this inherited condition. Deficiency of the interscalar septum in the distal coils of the cochlea (Mondini deformity) was found to be a common but probably not a constant feature of Pendred syndrome. However, enlargement of the endolymphatic sac and duct in association with a large vestibular aqueduct was present in all 20 patients examined by MRI. We conclude that thin section high resolution MRI on a T2 protocol in the axial and sagittal planes is the imaging investigation of choice.