Discovery of allelic variants of HOXA1 and HOXB1: genetic susceptibility to autism spectrum disorders.

BACKGROUND: Family studies have demonstrated that the autism spectrum disorders (ASDs) have a major genetic etiologic component, but expression and penetrance of the phenotype are variable. Mice with null mutations of Hoxa1 or Hoxb1, two genes critical to hindbrain development, have phenotypic features frequently observed in autism, but no naturally occurring variants of either gene have been identified in mammals. METHODS: By sequencing regions of genomic DNA of patients with autism spectrum disorders, we detected a substitution variant at HOXA1 and an insertion variant at HOXB1, both in coding regions of the genes. Fifty-seven individuals ascertained for a diagnosis of an ASD, along with 166 of their relatives, were typed for these variants. Two non-ASD populations were typed, and the frequency of the newly identified alleles was determined in all groups. The genotypes of the ASD families were tested for conformation to Hardy-Weinberg proportions and Mendelian expectations for gene transmission. RESULTS: The frequency of the variants was 10-25% in persons of European or African origin. In the ASD families, there was a significant deviation from the HOXA1 genotype ratios expected from Hardy-Weinberg proportions (P = 0.005). Among affected offspring, a significant deviation from Mendelian expectation in gene transmission (P = 0.011) was observed. No statistically significant effects were detected when the same analyses were applied to the HOXB1 locus, but there was evidence of an interaction between HOXA1, HOXB1, and gender in susceptibility to ASDs. CONCLUSIONS: The results support a role for HOXA1 in susceptibility to autism, and add to the existing body of evidence implicating early brain stem injury in the etiology of ASDs.

Ancestral and recombinant 16-locus HLA haplotypes in the Hutterites.

Prior studies in the Schmiedeleut Hutterites of South Dakota have demonstrated associations between human leukocyte antigen (HLA) haplotype matching and fetal loss (Ober et al. 1992) and mate preferences (Ober et al. 1997), as well as deficiencies of homozygotes for HLA haplotypes (Kostyu et al. 1993). These studies were based on the serologically-defined five-locus HLA-A, -C, -B, -DR, -DQ haplotype. To further elucidate the effects of specific major histocompatibility (MHC) loci or regions on fetal loss and mate choice, we genotyped a sample of Hutterites for 14 MHC loci by DNA or biochemical methods. Typing for additional loci in the HLA-A to HLA-DPB1 region increased the number of recognized Hutterite MHC haplotypes to 67, and further localized the site of crossover in 9 of 15 recombinant haplotypes. Hutterite MHC haplotype sequences are similar to those observed in outbred Caucasians, suggesting that the influence of HLA haplotypes on fetal loss and mating structure may be general.

Human leukocyte antigen matching and fetal loss: results of a 10 year prospective study.

The role that maternal and fetal human leukocyte antigen (HLA) genes play in pregnancy is unknown, but it has been suggested that fetuses whose HLA alleles do not differ from maternal alleles (i.e. histocompatible fetuses) are more likely to be aborted than fetuses with HLA alleles that differ from maternal alleles (i.e. histoincompatible fetuses). To elucidate the role of HLA compatibility in pregnancy, we tested the hypothesis that couples who match for HLA alleles or haplotypes would have reduced fertility because only these couples could produce histocompatible fetuses. We conducted a 10 year prospective study of HLA matching and pregnancy outcome in 111 Hutterite couples, providing information on 251 pregnancies. A logistic regression analysis was performed to determine the effects of HLA matching at HLA regions and loci on pregnancy outcome (fetal loss versus delivery). Significantly increased fetal loss rates were observed among couples matching for the entire 16-locus haplotype (P = 0.002). Among the individual loci, loss rates were increased among couples matching for HLA-B (P = 0.019), HLA-C (P = 0.033) and the complement component, C4 (P = 0.043). We interpret these results as evidence that matching for the entire 16-locus haplotype and/or alleles at an HLA-B-linked locus confers significant risk for fetal loss.

HLA and mate choice in humans.

Evidence from studies in rodents suggests that mate selection is influenced by major-histocompatibility-complex haplotypes, with preferences for dissimilar partners. This study was initiated to determine whether avoidance of a mate with the same HLA haplotype as one's own might be occurring in the Hutterites, a North American reproductive isolate of European ancestry, notable for their large sibships, communal lifestyle, and limited number of five-locus HLA haplotypes (HLA-A, -B, -C, -DR, and -DQ). HLA haplotypes were known for 411 Hutterite couples. The number of couples expected to match for a haplotype was calculated in two ways: first, from population genotype frequencies, with account being taken of the nonrandom mating pattern with respect to colony lineages, and, second, from computer simulations using conservative founder assumptions and the exact genealogy of the 411 couples. We observed fewer matches for HLA haplotypes between spouses than expected (first method, P = .005; second method, P = .020-.067). Among couples who did match for a haplotype, the matched haplotype was inherited from the mother in 29 cases and from the father in 50 cases (P = .018). These results are consistent with the conclusion that Hutterite mate choice is influenced by HLA haplotypes, with an avoidance of spouses with haplotypes that are the same as one's own.

Lean body mass in twins.

A study of 49 pairs of monozygous (MZ) twins and 38 pairs of same-sexed dizygous (DZ) twins showed that lean body mass (LBM), as determined by potassium 40 counting, is under genetic influence. Intrapair variances for LBM are much smaller than those for body fat, which suggests that LBM has a higher degree of heritability. There is a correlation between the magnitude of intrapair LBM differences and intrapair weight differences for both sets of twins, showing that environment is also an important influence. The effect of weight variation on LBM variation is greater for thin people than for those with appreciable burdens of body fat, an observation previously made on individuals who undergo a nutrition-induced weight change.

Analysis of HLA and disease susceptibility: chromosome 6 genes and sex influence long-QT phenotype.

The long-QT (LQT) syndrome is a genetically complex disorder that is characterized by syncope and fatal ventricular arrhythmias. LQT syndrome, as defined by a prolonged electrocardiographic QT interval, has a higher incidence in females than in males and does not exhibit Mendelian transmission patterns in all families. Among those families that are nearly consistent with Mendelian transmission, linkage between a locus for LQT syndrome and the H-ras-1 locus on the short arm of chromosome 11 has been reported in some families but not in others. Earlier analyses suggesting that LQT syndrome might be caused by a gene in the HLA region of chromosome 6 were not confirmed by standard linkage analyses. Here, we present an analysis of HLA haplotype sharing among affected pedigree members, showing an excess of haplotype sharing in a previously published Japanese pedigree and possibly also in 15 families of European descent. The haplotypes shared by affected individuals derive from both affected and unaffected parents. In an analysis of independent (unrelated) HLA haplotypes, we also found a nonrandom distribution of HLA-DR genes in LQT syndrome patients compared with controls, suggesting an association between the LQT phenotype and specific HLA-DR genes. Our data indicate that DR2 has a protective effect and, particularly in males, that DR7 may increase susceptibility to the LQT syndrome. Thus, LQT syndrome may be influenced by genes on chromosomes 11 and 6, possibly with a sex-specific effect. These results provide a model for an effect of HLA-region genes inherited from either parent on the expression of an illness that may be determined principally by alleles at loci not linked to HLA.

A genetic marker and family history study of the upstate New York multiple sclerosis cluster.

We report nine additional cases of new-onset multiple sclerosis (MS) among employees of an upstate New York manufacturing plant that uses zinc as a primary metal. These cases, identified during the decade 1980 to 1989, had clinical onset of the disease between 1979 and 1987. The new cases confirm the increased incidence of MS previously reported in the plant population for the 1970 to 1979 decade. The MS subjects in this occupationally based cluster do not seem different from other MS patients with regard to rates of familial MS or the frequencies of alleles for human leukocyte (HLA-DR) antigens or transferrin. The frequency distribution of alleles for transferrin (an iron- and zinc-binding protein) may differ in these and other MS subjects compared with controls.

Pathological changes of the mare endometrium and genotypes for transferrin and ELA.

Histological features of the endometrium, as assessed in biopsy samples, were related to Standardbred mare genotypes for transferrin, esterase (as a control) and equine leucocyte antigens (ELA). Pathological changes were found more frequently in each successively older age group of mares. Among mares aged 6-19 years, there were significant pathologic changes on first examination following an infertile breeding season for 46 of 90 (51%) of transferrin homozygotes and 50 of 146 (34%) of transferrin heterozygotes. The difference between the two groups was significant for the total data (chi 1(2) = 6.56, P = 0.010) and when the data were stratified for mare age at biopsy (chi 1(2) = 7.33, P = 0.0068). The effect of transferrin was similar in both trotters and pacers, especially for frequent genotypes commonly found in horses of both gaits. There was no effect of esterase and, in a smaller set of ELA-typed mares, no significant effect of ELA genotype on uterine biopsy category. Transferrin has a well-established microbiostatic and biocidal effect. Conceivably, heterozygotes for some combinations of transferrin variants could have a slower natural rate of endometrial deterioration than homozygotes.

Toronto-Rochester Depression study of 116 HLA-typed kindreds.

The Toronto-Rochester Depression study consisted of 116 pedigrees ascertained for multiple cases of major affective disorders. Among the 857 psychiatrically evaluated family members, of whom more than 85% were given a structured interview, 363 had major affective disorder by Research Diagnostic Criteria and 385 had no history of psychological aberration. HLA region genes were typed in 804 of these persons.

Analysis of the Toronto-Rochester Depression Study follow-up data confirms an HLA-region gene contribution to susceptibility to affective disorder.

Analysis of HLA haplotype distributions in relation to major affective disorder in affected sibling pairs and affected aunt or uncle and niece or nephew pairs confirmed that HLA-region genes do contribute to susceptibility to affective disorder. The data indicated that this effect may be greater in unipolar than in bipolar disorder, and more apparent in families with few affected members than in heavily loaded families. Nonrandom assortment of HLA haplotypes to affected and unaffected offspring in "low load" families occurred principally for the haplotype transmitted from the side of the family without affective disorder. We conclude that HLA-region genes contribute to but are not the only factor in susceptibility to major depression.

Multiple sclerosis and affective disorder. Family history, sex, and HLA-DR antigens.

To investigate a possible genetic cause underlying the clinical association between multiple sclerosis (MS) and affective disorder, we studied 56 patients with MS for psychiatric and genetic (family history, sex, and HLA-DR) characteristics. The 2:1 ratio of females to males expected for patients with MS was observed in this sample (40:16), but the excess of females occurred entirely among the 31 MS patients with major affective disorder (27 females and four males). Bipolar probands with MS had significantly more relatives with affective disorder or MS than did unipolar probands with MS. The HLA-DR antigen frequencies in patients with MS categorized by type and family history of affective disorder suggest that it may be possible to validate such clustering of patients. We concluded that sex and other genetic factors are related to the affective symptoms in MS and emphasize the importance of psychiatric evaluation of these patients.

Confirmation of the relationship of HLA (chromosome 6) genes to depression and manic depression. II. The Ontario follow-up and analysis of 117 kindreds.

HLA typing was conducted on 577 family members of 86 families having at least two first-degree family members with a lifetime history of major depression or bipolar disorder. The results were combined with a follow-up study of 10 Newfoundland kindreds and with the data obtained from our previous studies, giving a total cohort of 117 families of diverse ethnic and geographic origin. There was increased sharing of HLA haplotypes, as compared with random expectation, over all possible pairwise comparisons both in the follow-up studies (P less than 0.025) and in the total data (P less than 0.01). The increase in HLA haplotype sharing over random expectation was greater if comparisons within heavily loaded sibships (by prior convention, sibships with three or more affected siblings) were omitted from the analysis (P less than 0.002). There was also non-random transmission of HLA haplotypes in 50 families selected for a low-load, unaffected parent (P less than 0.005). Thus, we conclude that genes in the HLA region of chromosome 6 constitute one of the elements in the multifactorial etiology of affective disorder. This conclusion does not depend on any assumption concerning genetic heterogeneity or epistasis or on specific modes of transmission, penetrance values or linkage distances. In addition, the data suggest that chromosome 6 region genes may have a different effect in unipolar and bipolar illness.

Linkage between the loci for the Lp(a) lipoprotein (LP) and plasminogen (PLG).

A locus, LP, that determines quantitative variation of Lp(a) lipoprotein phenotypes is linked to the plasminogen (PLG) locus (peak lod score = 12.73). This linkage relationship assigns a locus with alleles that have an affect on risk for coronary artery disease to the long arm of chromosome 6.

Further studies of the plasma alpha 1 B-glycoprotein polymorphism: two new alleles and allele frequencies in Caucasians and in American blacks.

Two new alleles (A1 B*3 and A1 B*4) of human plasma alpha 1 B-glycoprotein (alpha 1 B) were reported. alpha 1 B phenotyping was done by using either a simple method of two-dimensional (2-D) agarose gel-horizontal polyacrylamide gel electrophoresis (PAGE) followed by protein staining or by one-dimensional horizontal PAGE and immunoblotting. Seven different alpha 1 B phenotypes (1-1, 1-2, 1-3, 1-4, 2-2, 2-3 and 3-3) were observed; phenotypes 1-3 and 1-4 were differentiated from each other only by the 2-D method. The respective frequencies Af A1 B*1, A1 B*2, A1 B*3 and A1 B*4 alleles in the studied populations were estimated as follows: American Blacks (New York) 0.732, 0.204, 0.064, 0; American Whites (New York) 0.947, 0.053; Czechs (Melník) 0.964, 0.034, 0, 0.002; Slovaks (Bratislava and Trencin) 0.977, 0.023, 0, 0. The population of American Blacks showed a much higher degree of alpha 1 B polymorphism (polymorphism information content = 0.37) than the Caucasian populations that have been studied.

Standardbred stallion gene transmission for twelve protein systems: evidence for selection in trotters.

The transmission ratios of alleles at 12 protein marker loci were computed individually for American Standardbred stallions in a genealogy of 5392 phenotyped horses. Over all loci there was significant gene transmission distortion for trotting stallions (p = 0.0019) but not for pacing stallions (p = 0.99). The transmission distortion was due to sire-specific effects (p = 0.0024) and not to increased transmission of one or the other allele of a given heterozygous genotype (p = 0.21). Individual-specific, non-random transmission of homologous chromosomes may provide a mechanism for selection to operate without requiring differential fitness for specific alleles or genotypes in the population as a whole.

ELA and fertility in American Standardbred horses.

We have analysed the effects of ELA alleles and sire-dam ELA incompatibility on two measures of fertility, gestation length and foaling rate, in American Standardbred horses. Using multivariate statistical methods, we corrected for the effects of confounding factors such as dam and sire age, parity, inbreeding, and sire-dam kinship. These analyses revealed substantial differences between Standardbred trotters and pacers in the effects of several confounding factors. There appear to be no ELA effects on gestation length in either trotters or pacers. However our results suggest that there may be ELA effects on foaling rate associated with specific dam alleles, with sire-dam incompatibility, and possibly with specific sire alleles, and that these effects differ between trotters and pacers.

The relationship of HLA to depression and manic depression. I. The Newfoundland follow-up.

This report constitutes the Newfoundland component of a large scale replication study to assess the relationship of HLA to affective disorders; the Ontario component will be published subsequently. In a collaborative study between the University of Toronto, Memorial University and the University of Rochester, first degree family members of Probands with major affective disorder in Newfoundland were assessed for the lifetime presence of psychiatric disorder; their blood was also typed for Human Leucocyte Antigens (HLA). Because of the high rate of refusal to participate, only 10 Newfoundland families could be assessed completely. While this number of families is too small to evaluate the role of HLA as a marker of susceptibility to affective disorder, the results will be added to those of the larger Ontario component. Some problems of conducting research in communities similar to those found in Newfoundland are briefly discussed in the context of characteristics of the Probands in the study group as compared with those of subjects who refused entry into the study.