The DYT1 gene on human chromosome 9q34 appears to be responsible for most cases of early onset primary torsion dystonia (PTD) both in Ashkenazi Jewish (AJ) and in non-Jewish patients. Previous haplotype analysis in a 2 cM region surrounding the DYT1 gene showed that a single founder mutation (DYT1AJ) was responsible for most cases of early onset PTD in the North American AJ population and refined the most likely location of the gene to a 150 kb interval between the marker loci D9S2161 and D9S63.

Recently, the majority of cases of early onset PTD in both AJ and non-Jewish patients were found to carry a unique 3-bp (GAG) deletion in the coding region of the DYT1 gene. This deletion appears to have arisen more than once, suggesting independent mutational events.

In this study, we analysed the haplotypes surrounding DYT1 in 9 AJ and 15 non-Jewish British patients carrying the GAG deletion in the DYT1 gene. We found that all AJ British patients carried the same haplotype as the North American Jews, sustaining the theory that the current British AJ community descends from the same small group of individuals as the North American Jewry. Furthermore, in the non-Jewish British patients, only a limited number of distinct founder mutations was observed. This supports the hypothesis that the GAG deletion in the DYT1 gene is not a very frequent mutation, and that it has arisen only a limited number of times throughout the centuries.

A group of 13 Moroccan patients with MPS I and their families, including three siblings and twin siblings, was screened for mutations of the α-L-iduronidase gene using fluorescence-assisted mismatch analysis (FAMA) and cycle sequencing of PCR products. The P533R mutation, which is rare in Europeans, was identified in 92% of mutant alleles (24/26). This is the highest frequency of this mutation detected in patients with Hurler syndrome. None of the patients carried the W402X or Q70X alleles, the most common MPS I mutations in Europeans. These results suggest that the P533R mutation constitutes the genetic lesion which results in MPS I in people of Moroccan descent and provides yet more evidence for the uneven geographical distribution of mutations in MPS I.

We applied a complex segregation analysis to 46 pedigrees with a total of 121 nuclear families and 660 individuals, to verify hypotheses regarding the inheritance of OFC and linkage with markers on chromosomes 6 and 2. The POINTER program for segregation analysis strongly rejected the hypothesis of no familial transmission of OFC in these families. When the hypothesis of a two-locus model was tested with COMDS, the analysis showed the presence of at least two loci and the model assuming a dominant major gene and a recessive modifier locus was statistically accepted. Given the fitted two-locus model, we tested for a possible linkage between the major OFC locus and the two markers studied. For D6S259, the estimate of the recombination fraction was θ=0.098, corresponding to a LOD score around 2.1. On the contrary, the data analysis concerning the D2S378 marker showed an estimate of the recombination fraction not significantly different from the independence hypothesis.

The population genetics of the HLA class II loci was studied with reference to variation in the frequency of (a) alleles at a locus and (b) amino acids at specific sites. Variation was surveyed at 4 loci (DRB1, DQA1, DQB1, and DPB1) in 22 populations from the Twelfth International Histocompatibility Workshop (Saint-Malo, 1996). Allele and amino acid variation was measured by computing heterozygosity and the effective number of alleles. Substantial variations in polymorphism were observed among the various populations and loci studied. In the majority of the populations, DRB1 has the highest heterozygosity and effective number of alleles. As previously shown, the Amerindian populations have lower levels of allelic diversity when compared to other populations. At the amino acid level, DRB1 antigen recognition sites (ARS) have the highest heterozygosities and effective number of alleles. For the other loci (DPB1, DQA1, and DQB1) for which there is no crystal structure and for which ARS sites were inferred from DRB1, non-ARS sites were often among the sites with highest levels of variation. It is possible that these putative non-ARS sites do play a role in antigen presentation.

The homozygosity test for neutrality was applied to allele and amino acid data. Of the four HLA class II loci studied, only DPB1 failed to show evidence of balancing selection. DQB1 and DQA1 depart significantly from neutrality in the largest number of populations. Genetic distances between populations were computed based on frequency of alleles and amino acids at ARS sites.

This study traces the evolutionary pathways of the apolipoprotein B gene in the low risk Chinese and high risk Asian Indians in relation to coronary artery disease (CAD). Haplotypes were constructed from six apoB polymorphisms sp24/27, Ag(c/g), Ag(a1/d), XbaI, Ag(h/i) and, Ag(t/z). These were genotyped from 474 Chinese (253 healthy, 221 CAD patients) and 248 Asian Indians (164 healthy, 84 CAD patients). The maximum parsimony method was used to construct a cladogram for each ethnic group. Three haplotypes in the Chinese and one in the Indians were found exclusively in CAD patients. These haplotypes were sp27ca1X-ht, sp24ga1X-iz and sp24ca1X+it in Chinese, and sp24cdX-it in Indians. Those in the Chinese all occurred as terminal haplotypes and represented the most recent mutations. Evolutionary pathways for both ethnic groups were similar for majority of the haplotypes except for the presence of an additional third branch in the Indians arising from the ancestral haplotype. However, this third branch does not appear to contribute to the susceptibility of the Indians to CAD.

Human paternal population history was studied in 9 populations [three Native American, three Asian, two Caucasian and one African-derived sample(s)] using sequence and short tandem repeat haplotype diversity within the non-pseudoautosegmal region of the Y chromosome. Complete coding and additional flanking sequences (949 base pairs) of the RPS4Y locus were determined in 59 individuals from three of the populations, revealing a nucleotide diversity of 0.0147%, consistent with previous estimates from Y chromosome resequencing studies. One RPS4Y sequence variant, 711C>T, was polymorphic in Asian and Native American populations, but not in African and Caucasian population samples. The RPS4Y 711C>T variant, a second unique sequence variant at DYS287 and nine Y chromosome short tandem repeat (YSTR) loci were used to analyze the evolution of Y chromosome lineages. Three unambiguous lineages were defined in Asian, Native American and Jamaican populations using sequence variants at RPS4Y and DYS287. These lineages were independently supported by the haplotypes defined solely by YSTR alleles, demonstrating the haplotypes constructed from YSTRs can evaluate population diversity, admixture and phylogeny.

In the paper by Goldstein et al. (Genomics, 1995), the authors carried out a simulation study to investigate the relative efficiencies of a no interference linkage analysis to an analysis with certain models that allow for interference. They showed that, for completely informative and independent recombination data, the analysis with the no interference model was inefficient, in the present of interference. In practice, the assumption of completely informative markers is unrealistic with data from human pedigrees. We report the results of a study investigating whether this conclusion still holds for gametes arising within pedigrees. We consider the same two mapping problems as Goldstein et al.: exclusion mapping and gene ordering. The results obtained were consistent with their findings, although the efficiency gains for analyses using the chi-square model were not as great in some cases. This is not unexpected with less than fully informative data. These results point to the need for research of developing new statistical and computational methods to incorporate interference into multipoint linkage mapping using pedigree data. This would make efficient use of available, but sometimes scarce data, especially in disease gene mapping.