Polymorphic admixture typing in human ethnic populations.

A panel of 257 RFLP loci was selected on the basis of high heterozygosity in Caucasian DNA surveys and equivalent spacing throughout the human genome. Probes from each locus were used in a Southern blot survey of allele frequency distribution for four human ethnic groups: Caucasian, African American, Asian (Chinese), and American Indian (Cheyenne). Nearly all RFLP loci were polymorphic in each group, albeit with a broad range of differing allele frequencies (delta). The distribution of frequency differences (delta values) was used for three purposes: (1) to provide estimates for genetic distance (differentiation) among these ethnic groups, (2) to revisit with a large data set the proportion of human genetic variation attributable to differentiation within ethnic groups, and (3) to identify loci with high delta values between recently admixed populations of use in mapping by admixture linkage disequilibrium (MALD). Although most markers display significant allele frequency differences between ethnic groups, the overall genetic distances between ethnic groups were small (.066-.098), and < 10% of the measured overall molecular genetic diversity in these human samples can be attributed to "racial" differentiation. The median delta values for pairwise comparisons between groups fell between .15 and .20, permitting identification of highly informative RFLP loci for MALD disease association studies.

Refined mapping of the gene causing familial Mediterranean fever, by linkage and homozygosity studies.

Familial Mediterranean fever (FMF) is an autosomal recessive disease characterized by attacks of fever and serosal inflammation; the biochemical basis is unknown. We recently reported linkage of the gene causing FMF (designated "MEF") to two markers on chromosome 16p. To map MEF more precisely, we have now tested nine 16p markers. Two-point and multipoint linkage analysis, as well as a study of recombinant haplotypes, placed MEF between D16S94 and D16S80, a genetic interval of about 9 cM. We also examined rates of homozygosity for markers in this region, among offspring of consanguineous marriages. For eight of nine markers, the rate of homozygosity among 26 affected inbred individuals was higher than that among their 20 unaffected sibs. Localizing MEF more precisely on the basis of homozygosity rates alone would be difficult, for two reasons: First, the high FMF carrier frequency increases the chance that inbred offspring could have the disease without being homozygous by descent at MEF. Second, several of the markers in this region are relatively nonpolymorphic, with a high rate of homozygosity, regardless of their chromosomal location.

Characterization of a class 3 tyrosine kinase.

In an effort to identify unique tyrosine kinases found in human leukemia cell lines, we utilized polymerase chain reaction (PCR) technology and degenerate oligonucleotide primers to produce a cDNA library of kinase catalytic domains found in the human monocytic cell line AML-193. This search yielded a member of the class 3 tyrosine kinases closely related to the murine kinase FD-22. Previous work has identified this kinase as JAK1. This class of tyrosine kinases is characterized by being ubiquitously expressed, lacking both a ligand-binding domain and a SH2 domain, while containing a second domain similar to a degenerate kinase domain. Our studies focused on the further characterization of this class 3 tyrosine kinase using Northern blot analysis to demonstrate an increase in steady-state mRNA by interferon-gamma in human monocytes. A human-hamster somatic cell hybrid panel and linkage mapping was used to assign JAK1 (aml-116) to human chromosome 1.

Organization of the human T cell receptor zeta/eta gene and its genetic linkage to the Fc gamma RII-Fc gamma RIII gene cluster.

The zeta-subunit is the most recently characterized stoichiometric human TCR component. In this study we describe the molecular organization of the human zeta-gene. The zeta transcript is generated as the spliced product of eight exons that are separated by distances of 0.7 kb to more than 8 kb. Ribonuclease protection studies revealed multiple transcription initiation sites distributed over a range of approximately 115 bases. A variable number tandem repeat restriction fragment polymorphism contained within the structural gene has allowed for the localization of zeta within the human genome. Additionally, a restriction fragment polymorphism within the Fc gamma RII-Fc gamma RIII gene cluster has allowed for its localization on the map of human chromosome 1q and for the establishment of its linkage to the zeta-gene locus. A region that is highly homologous on a nucleotide level with the eta-exon of the murine zeta-gene is localized to the 3' region of the human zeta-gene. Surprisingly, translation of this region into protein results in a structure that is markedly divergent from its murine counterpart. This finding has important implications regarding the potential role of eta in T cell function.

Population and pedigree studies reveal a lack of association between the dopamine D2 receptor gene and alcoholism.

Using the dopamine D2 receptor clone lambda hD2G1, Blum et al recently found that the D2/Taq I allele (A1) was present in 69% of 35 deceased alcoholics but in only 20% of an equal number of controls. To assess this association further, we evaluated the D2/Taq I polymorphism and a single-strand conformation polymorphism detected by polymerase chain reaction and nondenaturing gel electrophoresis (PCR-SSCP) of the 3' noncoding region of the D2 receptor gene. We studied 40 unrelated white alcoholics, 127 racially matched controls, and two white pedigrees. The Schedule for Affective Disorders and Schizophrenia-Lifetime Version (SADS-L) clinical diagnostic interviews were rated blindly by two clinicians. The SADS-L interviews and other data were then used to ascertain diagnoses according to the Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition (DSM-III-R) criteria. Alcoholics were subtyped according to age of onset, severity, presence of antisocial personality, and family history. No significant differences in either D2/Taq I or PCR-SSCP allele frequencies were observed between alcoholics, subpopulations of alcoholics, or controls. The PCR-SSCP polymorphism provided independent information against linkage at the D2 receptor locus. Several recombinants between the D2/Taq I locus and alcoholism were observed in two white families with an alcoholic parent who possessed the A1 allele. This study does not support a widespread or consistent association between the D2 receptor gene and alcoholism.