Carmela M. Castiglione

A global survey of haplotype frequencies and linkage disequilibrium at the DRD2 locus

Abstract A four-site haplotype system at the dopamine D2 receptor locus (DRD2) has been studied in a global sample of 28 distinct populations. The haplotype system spans about 25 kb, encompassing the coding region of the gene. The four individual markers include three TaqI restriction site polymorphisms (RSPs) – TaqI “A”, “B”, and “D” sites – and one dinucleotide short tandem repeat polymorphism (STRP). All four of the marker systems are polymorphic in all regions of the world and in most individual populations. The haplotype system shows the highest average heterozygosity in Africa, a slightly lower average heterozygosity in Europe, and the lowest average heterozygosities in East Asia and the Americas. Across all populations, 20 of the 48 possible haplotypes reached a frequency of at least 5% in at least one population sample. However, no single population had more than six haplotypes reaching that frequency. In general, African populations had more haplotypes present in each population and more haplotypes occurring at a frequency of at least 5% in that population. Permutation tests for significance of overall disequilibrium (all sites considered simultaneously) were highly significant (P<0.001) in all 28 populations. Except for three African samples, the pairwise disequilibrium between the outermost RSP markers, TaqI “B” and “A”, was highly significant with D’ values greater than 0.8; in two of those exceptions the RSP marker was not polymorphic. Except for those same two African populations, the 16-repeat allele at the STRP also showed highly significant disequilibrium with the TaqI “B” site in all populations, with D’ values usually greater than 0.7. Only four haplotypes account for more than 70% of all chromosomes in virtually all non-African populations, and two of those haplotypes account for more than 70% of all chromosomes in most East Asian and Amerindian populations. A new measure of the amount of overall disequilibrium shows least disequilibrium in African populations, somewhat more in European populations, and the greatest amount in East Asian and Amerindian populations. This pattern seems best explained by random genetic drift with low levels of recombination, a low mutation rate at the STRP, and essentially no recurrent mutation at the RSP sites, all in conjunction with an “Out of Africa” model for recent human evolution.

No association between alcoholism and multiple polymorphisms at the dopamine D2 receptor gene (DRD2) in three distinct Taiwanese populations

This study examined whether there is evidence for an association between alcoholism and the alleles of the TaqI A, TaqI B, and short tandem repeat polymorphisms (STRP), both individually and as haplotypes, at the dopamine D2 receptor gene (DRD2) in males of three populations from Taiwan. We studied 46 Chinese Han (21 alcoholics and 25 nonalcoholics), 42 Atayal (21 alcoholics and 21 nonalcoholics), and 40 Ami (20 alcoholics and 20 nonalcoholics). Alcoholism was diagnosed according to DSM-III-R criteria and all individuals in the alcoholic groups were severely affected. Significant linkage disequilibrium occurs for the three polymorphic sites in all three populations. No significant association was observed between any of the three polymorphisms at the DRD2 locus, tested individually and as haplotypes, and alcoholism in the three subject groups. We conclude that no association exists between genetic variation at the DRD2 locus and alcoholism in Chinese Han, Atayal, and Ami males.

Properties of monoamine oxidase in control and Lesch-Nyhan fibroblasts

Monoamine oxidase activity of the A type was measured in homogenates of cultured human skin fibroblasts. Twenty-four control lines had activities ranging over fifty-fold with an apparent bimodal distribution. Activity in fibroblasts from 20 patients with the Lesch-Nyhan syndrome fell in the low portion of the normal distribution with a mean activity about 50% that of the control mean (p<0.05). In a subgroup of control and Lesch-Nyhan lines with levels of enzyme activity from 0.9 to 179 pmol/min/mg protein, monoamine oxidase was similar with respect to apparent Km for tryptamine, thermal stability at 56 C, and sensitivity to clorgyline. Thus the lower mean levels of activity observed in the Lesch-Nyhan as compared to control fibroblasts were not associated with other altered properties of the enzyme. The bimodal distribution of enzyme activity suggests that a genetic polymorphism for monoamine oxidase may control levels of activity expressed in fibroblasts.

Monoamine oxidase and catechol-O-methyltransferase activities in cultured human skin fibroblasts.

Abstract Human fibroblasts obtained from normal male children and children with the Lesch-Nyhan syndrome were found to contain both the A and B forms of monoamine oxidase, with the A form predominating. Both forms of monoamine oxidase showed decreased activities in Lesch-Nyhan, as compared to normal cells; while catechol-O-methyltrans-ferase activities were similar. This study demonstrates the usefulness of fibroblasts cultured from human skin biopsies in analyses of alterations in catecholamine catabolism associated with inherited neurologic diseases.

Monoamine oxidase type a in fibroblasts from patients with bipolar depressive illness

No differences in levels of type A monoamine oxidase (MAO) were observed in cultured human skin fibroblasts from nine patients with bipolar depressive illness as compared to 18 age-, sex-, and race-matched controls. All cells were biopsied and cultured under parallel conditions. Fibroblasts from monozygotic twins (three sets) had levels of MAO activity that were highly concordant, indicating that levels measured in fibroblasts are genetically determined. Together these findings suggest that an inherited predisposition to bipolar depressive illness does not involve inherited variations in levels of type A MAO activity. Using a larger control population, a positive correlation was observed between age of donor and level of MAO activity. This finding demonstrates the need for age-matched control and patient groups when comparing levels of type A MAO in fibroblasts.

MONOAMINE OXIDASE ACTIVITY IN NORMAL and LESCH-NYHAN FIBROBLASTS

Monoamine oxidase (MAO) activity was studied in cultured skin fibroblasts from 10 Lesch‐Nyhan patients, a Lesch‐Nyhan variant and 11 controls matched for age. sex and race. Activity (predominantly type A) was measured in cell homogenates using tryptamine as the substrate. For each line activity varied with the conditions of culture. Activity increased 3‐10 fold as cultures went from logarithmic to stationary phase of growth. When cultures were confluent, activity was lowered by frequent feedings or the use of fresh medium and serum. Activity for each line remained fairly stable during successive passages, but rose 3‐8 fold as cultures became senescent. When comparing activity between control and Lesch‐Nyhan lines, cells were cultured under standardized conditions. The mean value of MAO activity in Lesch‐Nyhan lines was approximately one fourth of the mean activity in control lines (P < 0.012), In the control population, the distribution of activity appeared to be bimodal. Activities in the Lesch‐Nyhan lines fell completely within the lower portion of the control distribution. Cells from a Lesch‐Nyhan patient who lacked several of the neurologic symptoms of the disease (including self‐mutilation) had an MAO activity 6 fold greater than the control mean. although his hypoxanthine phosphoribosyltransferase activity was <3% of control levels.

Status of the search for a major genetic locus for affective disorder in the Old Order Amish.

SummaryWe have resumed the search for an autosomal linkage with affective disorder in the Old Order Amish and report the pairwise linkage results after screening 185 marked loci. No positive evidence of genetic linkage was found, and we estimate that roughly 23% of the autosomal genome has been excluded from linkage.

A linkage group of five DNA markers on human chromosome 10.

Five chromosome 10 DNA markers (D10S1, D10S3, D10S4, D10S5, and RBP3) were typed in five large pedigrees with multiple endocrine neoplasia type 2A (MEN-2A) and in five non-MEN-2A pedigrees. Linkage analyses showed that these loci and the locus for MEN-2A (MEN2A) are in one linkage group spanning at least 70 cM. The order of the marker loci is RBP3-D10S5-D10S3-D10S1-D10S4, with interlocus recombination frequencies of 7, 13-19, 19, and 19%, respectively, all on the same side of MEN2A. Analyses of sex-specific recombination frequencies indicated no significant differences between males and females for any of the map intervals studied. Previous localization of D10S5 and RBP3 to the proximal region of the long arm and the pericentric region, respectively, comparison of results with other studies, and our preliminary results with other chromosome 10 markers suggest that the D10S4 end of the map extends into the long arm. Our linkage map has been constructed using only two- and three-locus analyses. It will be possible to combine our results with those of other groups to construct a more detailed and accurate genetic map of chromosome 10.

Glucocorticoid receptor maps to the distal long arm of chromosome 5

Carte genetique du recepteur des glucocorticoides etudie par analyse de linkage avec des marqueurs RFLP dans 3 etudes familiales

The Locus for the Medium-Chain Acyl-CoA Dehydrogenase Gene on Chromosome 1 Is Highly Polymorphic

The gene for medium-chain acyl-CoA dehydrogenase (gene symbol ACADM; enzyme symbol MCAD) has been characterized for restriction fragment length polymorphisms (RFLPs) and mapped by linkage analysis to 4.2 cM from D1S2 and 11.7 cM from PGM1. The three RFLP systems described in detail show significant linkage disequilibrium but define four haplotypes with a PIC of 0.58. This makes ACADM informative for linkage mapping and for clinical genetic studies. By linkage studies, the orientation of these three loci relative to the centromere places ACADM most proximal. This is in direct conflict with the regional assignments of ACADM to 1p31 by in situ hybridization and of PGM1 to 1p22.1 by somatic cell studies. We suggest that this somatic cell localization of PGM1 may be incorrect.