Segregation and linkage analyses of dopamine-beta-hydroxylase activity.

Dopamine-beta-hydroxylase (DBH) activity in serum was measured by spectrophotometric methods in 95 persons of a large family (HGAR 2), along with 27 polymorphic markers from blood, urine and saliva. The distribution of DBH activity, after appropriate transformation and age adjustment, showed a significantly better fit to a mixture of two normal distributions than a single normal distribution. Pedigree segregation analyses showed evidence of a possible major gene governing low levels of DBH activity, segregating in this family in a recessive fashion. Linkage analyses between that major locus and the 27 polymorphic markers showed no significant lod scores favoring linkage. The highest lod score obtained was 0.81 with Lp at zero recombination fraction. In addition, published data on DBH activity measured by radiochemical assays on 22 families with 161 members were reanalyzed as a quantitative trait, with appropriate correction for ascertainment bias. The results were similar to that of HGAR 2, corroborating the existence of a major locus for DBH activity.     

Segregation and linkage analyses of 72 leprosy pedigrees

Data on 72 families with multiple cases of leprosy were analyzed for a susceptibility gene linked to the HLA loci. We conducted segregation analysis with the program POINTER and identity of HLA types by descent analysis to determine the most likely mode of inheritance. We then conducted linkage analysis with the program LINKAS, first assuming linkage equilibrium and then allowing for linkage disequilibrium and etiological heterogeneity. Segregation results suggest a recessive mode of inheritance, especially for the tuberculoid forms of leprosy. The linkage results, limited to tuberculoid forms and assuming a recessive model, suggest a hypothesis of loose linkage with no unlinked locus. When an additive model is assumed, the best fit is obtained with a hypothesis of complete linkage (theta = 0.0) with heterogeneity. We currently favor the additive model as the more plausible one.     

Segregation and linkage analysis.

Computer programs are available in the software package SAGE to perform a variety of segregation and linkage analyses used by human geneticists. These methods are designed specifically to uncover major gene segregation in pedigree data coming from non-inbred populations. With the aid of a closely linked polymorphic marker, they can detect a locus that contributes as little as 10% to the variation of a quantitative trait in a pedigree sample of several hundred individuals.     

Estimation of segregation and linkage parameters in simulated data. I. Segregation analyses with different ascertainment schemes.

We report the results of a simulation study designed to assess the capability of segregation analysis to detect Mendelian transmission and to estimate genetic model parameters for complex qualitative traits, characterized by heritability in the range 0.20-0.45 and low heterozygote penetrance. The pedigree analysis package, PAP, was used to perform the analyses. For all data sets, models of no transmission could be rejected. In most cases, models of Mendelian transmission could not be rejected; however, several samples approached significance levels. When Mendelian transmission was assumed, reasonably good parameter estimates were obtained, although heterozygote penetrances were often overestimated. Different sampling schemes were imposed on the simulated data in order to examine the extent of information loss with the reduction in sample size. One of these strategies (a sequential sampling scheme) appears to have resulted in critical loss of information in some cases.     

Segregation and linkage analyses in two complex populations derived from the citrus rootstock Cleopatra mandarin. Inheritance of seed reproductive traits

Two complex populations derived from the salt-tolerant citrus rootstock Cleopatra mandarin were used to investigate (1) the genomic regions affected by segregation distortion and (2) gene segregation heterogeneity and their causes and to obtain (3) a Citrus reshni linkage map to genetically analyze (4) the duration of the juvenility period and the seed embryony type. Both populations differed in the extent and origin of segregation distortion. The population derived from the cross between C. reshni and Poncirus trifoliata (R?×?Pr) showed 75?% of codominant markers with distorted segregation. The origin of this distortion was prezygotic in most cases. Meanwhile, 100?% of codominant markers in the self-pollinated population [F₂(R?×?Pr)] showed genotypic distortion, and the origin of such distortion was mostly postzygotic, with the heterozygote being the most frequent genotype in all cases. In the R?×?Pr population, where two pollinator varieties were used, allele segregation was significantly heterogeneous not only in P. trifoliata (28.6?% of markers) but also in C. reshni (19.5?%). The results on segregation heterogeneity in the F₂(R?×?Pr) suggest the presence at linkage group 4c of a postfertilization system of balanced lethal factors that reduces homozygosis in self-compatible hybrids. Four low to medium contributing quantitative trait loci (QTLs) were detected for the duration of juvenility period by both Kruskal?CWallis and interval mapping methodologies. For seed embryony type, three QTLs were detected by both methodologies, with the previously reported Apo2 being the QTL contributing the most. CR14,290 and TAA15 are good markers for early selection of polyembryonic rootstocks in progenies derived from C. reshni, Citrus aurantium, and Citrus volkameriana.     

Segregation and linkage analyses in families of patients with bipolar,unipolar, and schizoaffective mood disorders.

Hypotheses of single major locus transmission (autosomal and X chromosome) of major affective disorder (i.e., bipolar, unipolar, and schizoaffective) are tested using the Elston-Stewart likelihood method of pedigree segregation analysis. The sample consists of families of varying size ascertained through patients treated at the National Institute of Mental Health in Bethesda, Maryland. We test hypotheses on subsamples of families according to: (1) diagnosis of proband (75 bipolar I, 22 bipolar II, 18 unipolar, and six schizoaffective); (2) extreme value of a biological trait in the proband ("low" monoamine oxidase, "low" cerebrospinal fluid serotonin metabolite 5-HIAA); and (3) positive response to lithium in the proband. We cannot find evidence for single major locus transmission of major affective disorder from segregation analysis in any subsample of family even when the diagnostic classification of ill phenotypes is widened to include possible affective "spectrum" diagnoses. In addition, linkage studies of 21 autosomal markers do not provide evidence for single major locus transmission of illness. The maximum lod score, found for 30 families at the MNS locus, was 1.39 at 20% recombination.     

Confirmation of linkage in von Hippel-Lindau disease

Von Hippel-Lindau (VHL) disease was initially reported to be linked to the RAF1 oncogene (3p25). We have ascertained and sampled two large multigenerational VHL families for linkage studies, in order to confirm the localization of the VHL gene as a prelude to fine mapping studies. The probes used in the analysis were p627 (RAF1) and pHeA12 (thyroid hormone receptor B) (3p24.1-3p22). VHL was analyzed as an autosomal dominant trait with age-dependent penetrance. The maximum lod score combining both families was z(theta) = 2.16 at theta = 0.0 for RAF1 and z(theta) = 2.20 at theta = 0.05 for thyroid hormone receptor B. Multipoint analysis using the RAF1 and thyroid hormone receptor B loci resulted in a peak lod score of 3.1 confirming linkage of VHL to this region of chromosome 3. However, the position of VHL relative to the two loci could not be established with certainty.     

Proteomic identification of a role for the von Hippel Lindau tumour suppressor in changes in the expression of mitochondrial proteins and septin 2 in renal cell carcinoma

The von Hippel Lindau (VHL) tumour suppressor gene, VHL, plays a central role in development of sporadic conventional renal cell carcinomas (RCCs). Studying VHL function may, therefore, increase understanding of the pathogenesis of RCC and identify markers/therapeutic targets. Comparison of 2-DE protein profiles of VHL-defective RCC cells (UMRC2) transfected with control vector or wild-type VHL showed differences in 30 proteins, including several novel changes. One of the findings confirmed by Western blotting was up-regulation of the mitochondrial protein ubiquinol cytochrome c reductase complex core protein 2 following VHL transfection, a change that was also observed in two other cell line backgrounds. A marked decrease in expression of this and several other mitochondrial proteins was demonstrated in RCC tissues and using VHL-transfectants, several were shown to exhibit VHL-dependent regulation. Thus, VHL may contribute to the decreased mitochondrial function seen in RCC. A form of septin 2 down-regulated following VHL transfection was also identified. Septin 2 was up-regulated in 12/16 RCCs, while alteration of the form present was also observed in 1/3 tumours analysed. Thus, increased expression of septin 2 is a common event in RCC and protein modification may also alter septin 2 function in a subset of tumours.     

Segregation,linkage, and diversity of allozymes in knobcone pine

Summary Female gametophytes of knobcone pine were used to study genetic variation at 58 loci in 26 enzyme systems. Mendelian segregation and linkage were tested at 21 loci. Got1, Pgi2, Mnr3, Adh2, and Lap2 were linearly arrayed in a single linkage group. Est and Acp3, and Flest and Lap1, formed two independent linkage groups. Although Mendelian segregation was the rule, several cases of segregation distortion were observed. Pooled over trees, Lap1 and Aap1 showed significant distortion. Of 11 cases of distortion observed for individual trees, 10 showed an excess of common alleles. Pooled over both loci and trees, giving a total sample of 17,183 gametes, the common alleles were significantly overrepresented by 1.1%, and heterogeneity was highly significant. Our results, and others in the literature, suggest that segregation distortion may affect the genetic structure of conifer populations.