Evidence for involvement of a second genetic locus on chromosome 11q in porphyrin metabolism

Chester porphyria is a distinct type of acute porphyria, which shows a biochemical overlap with acute intermittent and variegate porphyrias and has a dual enzyme deficiency of porphobilinogen deaminase (PBGD) and protoporphyrinogen oxidase. Linkage analysis in an extensive family with Chester porphyria was undertaken using multiple polymorphic markers. A maximum two point Lod score of 5.25 at 0.07 recombination (confidence interval 0.01 to 0.14) was observed with D11S351, which has been localised to 11q23.1. Multipoint linkage analysis confirmed the two point results and gave a maximum Lod score of 7.33 at a distance less than 1 cM proximal to D11S351. PBGD also maps to 11q but four recombinants could be identified from ten informative meioses in this family using a PBGD DNA polymorphism. Thus, a separate locus on 11q appears to be the basis of Chester porphyria.

Second-trimester unconjugated oestriol levels in maternal serum from chromosomally abnormal pregnancies using an optimized assay

Second-trimester unconjugated oestriol (UE3) levels were measured retrospectively in maternal serum from 78 chromosomally abnormal pregnancies and 390 matched controls using a radioimmunoassay kit (Amersham AMERLEX-M) optimized for use in the second trimester. Reduced levels of UE3 were found in a group of 49 Down's syndrome pregnancies with a median UE3 level of 0.79 multiples of the median (MOM) of the controls. Four trisomy 18 pregnancies had UE3 levels less than 0.7 MOM. There was a highly significant level of correlation between alpha-fetoprotein (AFP) and UE3 levels in the controls (r = 0.25, p < 0.01), the Down's syndrome pregnancies (r = 0.44, p < 0.01), and the other chromosome abnormalities (r = 0.61, p < 0.01). When used as an additional marker to AFP and human chorionic gonadotrophin in screening for Down's syndrome, UE3 does not appear to add to the sensitivity of such screening.

The angiotensin I converting enzyme gene and predisposition to high blood pressure

Phenotypic abnormalities of the renin-angiotensin system have been associated with the predisposition to high blood pressure. The angiotensin I converting enzyme (ACE) gene has been implicated as a candidate gene. We examined the distribution of common alleles of the ACE gene and measured circulating components of the renin-angiotensin system and urinary sodium excretion in 170 young Caucasian adults with contrasting genetic predisposition to high blood pressure. Predisposition was defined on the basis of personal and parental blood pressure levels by using the four corners sampling method. Young adults with greatest predisposition who had high blood pressure and two parents with high blood pressure did not show any significant difference in the distribution of the markers of the ACE gene, either as genotype or allele frequencies, when compared with young adults with least predisposition who had low blood pressure and two parents with low blood pressure. Offspring with urinary sodium excretion above the median (143.4 mmol per day) also showed no significant differences in the distribution of ACE alleles or genotype between groups. Different genotypes were associated with different average serum ACE concentrations (p < 0.0001), but plasma angiotensin II and aldosterone showed no significant variation with ACE genotype. These results suggest that in a group of Caucasians selected from the general population, the ACE gene is not associated with genetic predisposition to high blood pressure. In this population common ACE gene allelic markers would not be useful indexes of susceptibility to hypertension.

Identification of markers flanking the tuberous sclerosis locus on chromosome 9 (TSC1)

Analysis of a large tuberous sclerosis pedigree confirmed linkage to a locus on the long arm of chromosome 9, with recombination events placing the disease gene distal to gelsolin and proximal to dopamine beta-hydroxylase.

Scottish frequency of the common G985 mutation in the medium-chain acyl-CoA dehydrogenase (MCAD) gene and the role of MCAD deficiency in sudden infant death syndrome (SIDS)

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, is an autosomal recessive inborn error of metabolism associated with various clinical presentations, including sudden unexplained death in young children. We have determined the Scottish frequency of the common G985 mutation found in Caucasians and in samples from Scottish patients with sudden infant death syndrome (SIDS). The heterozygote frequency of the mutation was found to be 1 in 276 (95% confidence interval: 1/76-1/2279) in 552 healthy controls and 1 in 74 (95% confidence interval: 1/27-1/377) in 233 SIDS patients: a difference that was not statistically significant (Fisher's exact test; two-sided; p = 0.316). None of the SIDS samples was found to be homozygous for the G985 mutation.

Screening for molecular pathologies in Lesch-Nyhan syndrome

Heteroduplex detection by hydrolink gel electrophoresis was performed to screen for small mutations in 12 Lesch-Nyhan syndrome families with characterised molecular pathology which included nine point mutations, two small deletions, and a 1-bp insertion. This modified protocol for heteroduplex detection by hydrolink gel electrophoresis detected all 12 of these mutations and was utilised to rapidly determine the carrier status of females from affected families. On the basis of these results this approach appears to be a rapid and reliable screening method for point mutations in addition to small length mutations and for carrier detection in Lesch-Nyhan syndrome.

A YAC contig in Xp21 containing the adrenal hypoplasia congenita and glycerol kinase deficiency genes

The gene loci for adrenal hypoplasia congenita (AHC) and glycerol kinase deficiency (GK) map in Xp21 distal to Duchenne muscular dystrophy (DMD), and proximal to DXS28 (C7), by analysis of patient deletions. We have constructed a yeast artificial chromosome (YAC) contig encompassing a 1.2 Mb region extending distally from DMD, and containing DXS708 (JC-1), the distal junction clone of a patient with GK and DMD. A pulsed-field gel electrophoresis map of the YAC contig identified 3 potential CpG islands. Whole YAC hybridization identified cosmids both for construction of cosmid contigs, and isolation of single copy probes. Thirteen new single copy probes and DXS28 and DXS708 were hybridized on a panel of patients; the deletion mapping indicates that the YAC contig contains both GK and at least part of AHC, and together with the physical map defines a GK critical region of 50-250 kb. In one AHC patient with a cytogenetically detectable deletion we used the new probes to characterize a complex double deletion. Non-overlapping deletions observed in other unrelated AHC patients indicate that the AHC gene is large, extending over at least 200-500 kb. This mapping provides the basis for the identification of the AHC and GK genes.

Detection of seven point mutations in the porphobilinogen deaminase gene in patients with acute intermittent porphyria, by direct sequencing of in vitro amplified cDNA

Direct cDNA sequencing has been performed on asymmetrically amplified transcripts from the human porphobilinogen deaminase gene. Lymphocytes from 30 patients with acute intermittent porphyria were the source of mRNA; of the seven separate point mutations detected, three were silent, whereas four resulted in amino acid changes. Three of these changes involved highly conserved amino acids, and the remaining one a conserved charge. One of these mutations was predicted to cause structural alterations in the protein product. The application of this method to affected families allows the direct identification of these heterogeneous mutations, thus permitting the unequivocal detection of carriers.

Tightly linked polymorphic markers for fragile X syndrome and prenatal cytogenetic diagnostic experience

Linkage analysis using the polymorphic loci DXS369, DXS296, DXS297 and DXS306 was carried out on a cohort of 17 families segregating for fragile X syndrome. The observed recombination fractions at: DXS369 (Zmax = 3.02; theta = 0.06), DXS297 (Zmax = 2.92; theta = 0.0), DXS296 (Zmax = 3.82; theta = 0.0), DXA306 (Zmax = 4.55; theta = 0.05) confirm that these loci are tightly linked to FRAXA. Our experience in the cytogenetic analysis of 58 at risk pregnancies by chorionic villus or fetal blood sample examination documents a false negative rate in obligate carrier male pregnancies for CVS of 11% and for FBS of 3%.

Evidence for genetic heterogeneity in hereditary hydronephrosis caused by pelvi-ureteric junction obstruction, with one locus assigned to chromosome 6p

Hereditary hydronephrosis (MIM 143400) is an autosomal dominant trait that causes unilateral or bilateral pelvi-ureteric junction (PUJ) obstruction. Linkage analysis was undertaken in 5 families with hereditary PUJ obstruction using the major histocompatibility complex locus as a test marker. The data as a whole supported a hereditary hydronephrosis locus on 6p. Maximal lod scores were 3.090 at a recombination fraction of 0.1 with full penetrance, and 2.486 at a recombination fraction of 0.1 with a penetrance of 90%. However, analysis of two point lod scores using the HOMOG program revealed significant evidence for genetic heterogeneity with one locus on 6p in 4 of the families, and a different locus in one family. After exclusion of this unlinked family, two point analysis gave a maximal lod score of 3.9 at a recombination fraction of 0.05 with full penetrance, and 4.2 at a recombination fraction of 0.0 with 90% penetrance. These data support the assignment of one of the loci for hereditary hydronephrosis to chromosome 6p.

Genetic variation at fibrinogen loci and plasma fibrinogen levels

In view of the controversy regarding genetic variation at the fibrinogen loci and plasma fibrinogen levels, we have analysed DNA polymorphisms at the alpha (TaqI), beta (BclI and HaeIII), and gamma (KpnI/SacI) fibrinogen loci in 247 subjects whose plasma fibrinogen was determined by clotting and nephelometric assays. Strong linkage disequilibrium was found between the alpha/TaqI and gamma/KpnI/SacI markers and between the beta/BclI and beta/HaeIII markers. A lesser association was found between the alpha/TaqI and beta/BclI loci, beta/BclI and gamma/KpnI/SacI markers, alpha/TaqI and beta/HaeIII markers, and the gamma/KpnI/SacI and beta/HaeIII markers. This is consistent with the known physical order of these loci and suggests a relative excess of recombination in the alpha/gamma to beta interval. Plasma fibrinogen levels, by either assay method, when corrected or uncorrected for age, sex, and smoking habit, did not show any statistically significant associations with the four fibrinogen polymorphisms examined at the alpha, beta, and gamma fibrinogen loci either singly or when analysed as a haplotype.

Variation in the levels of pregnancy-specific beta-1-glycoprotein in maternal serum from chromosomally abnormal pregnancies

Human pregnancy-specific beta-1-glycoprotein (SP1) was assayed retrospectively in stored maternal serum (MS) samples from 82 chromosomally abnormal pregnancies and 377 matched controls. The median MSSP1 concentration in 48 Down's syndrome pregnancies was significantly elevated at 1.17 multiples of the control median (MOM), and significantly reduced (0.5 MOM) in a group of eight cases of unbalanced translocations. There was no significant difference in median SP1 concentrations in cases of trisomy 18, trisomy 13, balanced translocations, or sex chromosome abnormalities. A comparison with human chorionic gonadotrophin results in the same series of samples indicates that SP1 is a less sensitive predictor of Down's syndrome pregnancies.

Abnormalities of glucocorticoid metabolism and the renin???angiotensin system: a four-corners approach to the identification of genetic determinants of blood pressure

AIM

To assess the feasibility and utility of a new method to identify factors associated with increased predisposition to high blood pressure in young people.

SUBJECTS

Eight hundred and sixty-four people aged 16-24 years and their parents.

SETTING

Ladywell Medical Centre, Edinburgh, Scotland, UK.

METHOD

Blood pressure was measured in 864 young adults and in both of their parents. Four groups of approximately 50 offspring were selected from the corners of a scatter diagram, with offspring blood pressure scores on one axis and combined parental blood pressure scores on the other. Blood and urine samples were taken for biochemical and genetic analyses.

RESULTS

Two groups of offspring had parents with high blood pressure and two groups had parents with low blood pressure. When parental blood pressure was low, comparison of offspring with high and low blood pressure revealed significantly higher mean body mass index in offspring with high blood pressure, but no significant elevation of biochemical or hormonal variables. When parental blood pressure was high, comparison of offspring with high and low blood pressure also revealed a significant difference in body mass index, but in addition, offspring with high blood pressure and high parental blood pressure had higher levels of angiotensinogen, cortisol and 18-OH corticosterone. Restriction fragment length polymorphism analysis revealed that 27% of offspring at the greatest genetic risk (high personal and parental blood pressure) were homozygous for the larger allele of the glucocorticoid receptor gene compared with only 9% of those at lowest genetic risk (low personal and parental blood pressure).

CONCLUSION

The combined biochemical and genetic findings suggest that abnormalities of glucocorticoid metabolism and the renin-angiotensin system may help to explain genetic predisposition to high blood pressure. The new sampling method is practicable and could be applied to the investigation of other continuously distributed variables which show familial aggregation.

Regional chromosomal assignment of the human platelet phosphofructokinase gene to 10p15

A cDNA for human platelet 6-phosphofructokinase (PFKP) has been isolated from a human Raji cell line cDNA library. Using this cDNA as a probe, the gene for human PFKP, previously mapped to chromosome 10pter-p11.1, has been further localized to 10p15 by non-isotopic in situ hybridization.

Fibrinogen genotype and risk of peripheral atherosclerosis

There is conflicting evidence about the influence of fibrinogen genotype on plasma fibrinogen concentrations, and the relation between genotype and atherosclerotic disease has not been studied. In a population-based case-control study we aimed to find out whether certain fibrinogen genotypes are associated with an increased risk of peripheral atherosclerosis. 121 subjects with peripheral arterial disease and 126 healthy controls matched for age and sex were selected from a random population sample aged 55-74 years in the Edinburgh Artery Study. Mean fibrinogen concentrations were higher in cases than in controls (3.12 [95% confidence interval 2.99-3.26] vs 2.75 [2.64-2.85], p less than 0.001). A greater proportion of cases than controls were homozygous or heterozygous for an allele at the beta fibrinogen locus (4.2 kb allele, Bcl I digestion); the allele frequency was 0.197 in cases and 0.097 in controls (p less than 0.005). Extended haplotypes for 4.2 kb heterozygotes were also associated with an increased risk of peripheral arterial disease. However, haplotype had only a small effect on the association of plasma fibrinogen concentration with disease, and the relation of haplotype with disease was independent of age, sex, social class, smoking status, plasma fibrinogen, alcohol consumption, body mass index, and diabetes mellitus. We conclude that variation at the beta fibrinogen locus is associated with an increased risk of peripheral atherosclerosis. The influence is not mediated simply by way of increased fibrinogen concentrations but could be due to a structurally variant fibrinogen or linkage disequilibrium with a neighbouring gene.

The psychosocial sequelae of a second-trimester termination of pregnancy for fetal abnormality

A retrospective study to investigate the psychosocial sequelae of a second-trimester termination of pregnancy (TOP) for fetal abnormality (FA) is described. After appropriate consent was obtained, 84 women and 68 spouses were visited 2 years after the event and asked to complete an extensive questionnaire. Most couples reported a state of emotional turmoil after the TOP. There were differences in the way couples coped with this confusion of feelings. After 2 years about 20 per cent of the women still complained of regular bouts of crying, sadness, and irritability. Husbands reported increased listlessness, loss of concentration, and irritability for up to 12 months after the TOP. In the same period, there was increased marital disharmony in which 12 per cent of the couples separated for a while and one couple obtained a divorce. These problems could be attributed to a lack of synchrony in the grieving process. Confusing and conflicting feelings led to social isolation and lack of communication. Difficulties in coming to terms with the fetal loss were not found to be linked to the type of fetal abnormality or religious beliefs but were related to parental immaturity, inability to communicate needs, a deep-rooted lack of self-esteem before the pregnancy, lack of supporting relationships, and secondary infertility. Suggestions for improved management are given.

Genotype prediction in the fragile X syndrome

Fragile X positive, mentally retarded males have been shown to have an insertion or amplification of DNA sequences at, or close to, the site of expression of the fragile site. We show here the application of the detection of such changes to the diagnosis of affected males and female carriers and the identification of normal transmitting males. One fragile X negative male with the clinical features of the Martin-Bell syndrome also possesses an inserted/amplified DNA sequence. The implications of these results for screening for the fragile X syndrome are discussed.