Familial clustering of breast and prostate cancers and risk of postmenopausal breast cancer

BACKGROUND

Previous studies have suggested that cancers of the breast and prostate cluster in families and that the presence of both diseases in a family may be associated with increased risk of breast cancer.

PURPOSE

Our purpose was to evaluate whether 1) prostate cancer aggregates in families with postmenopausal breast cancer, 2) families with cancers of the breast and prostate are the same ones as families with cancers of the breast and ovary, and 3) a family history of prostate cancer is associated with increased risk of postmenopausal breast cancer.

METHODS

We analyzed data from a large prospective cohort study of Iowa women that were (at baseline) aged 55-69 years in 1986. At the third follow-up survey in 1992, self-reported data on family history of breast, ovarian, and prostate cancers in parents and siblings were provided by 30,883 women. Additional information was collected to ascertain whether the age-of-onset of breast cancer in mothers or sisters was before or after the age of 45 years. Cancer occurrence was documented using the State Health Registry of Iowa.

RESULTS

History of prostate cancer in their father or a brother was reported by 3384 (11.0%) of the women, and a total of 4090 women (13.2%) reported breast cancer in their mother or a sister. A positive family history of both cancers was reported by 556 women, significantly (two-sided P < .001) greater than the 457 women expected if the family histories were independent. The aggregation of breast, prostate, and ovarian cancers was reported by 22 participants, greater than the 2.7 expected (two-sided P < .0001). During 6 years of follow-up, 578 breast cancers were identified in the cohort at risk. Compared with women without a family history of either cancer, women with a family history of breast cancer had a relative risk (RR) of 1.37 (95% confidence interval [CI] = 1.06-1.79) if the affected relative had onset after the age of 45 years, and an RR of 1.71 (95% CI = 1.13-2.61) if the affected relative had onset at or before the age of 45. A family history of prostate cancer in the absence of a family history of breast cancer was associated with an RR of 1.19 (95% CI = .90-1.56). However, a family history of both breast and prostate cancers was associated with RRs of 2.06 (95% CI = 1.23-3.45) and 2.35 (95% CI = .97-5.67) for breast cancer onset in relatives of greater than 45 and less than or equal to 45 years, respectively.

CONCLUSIONS

These observations are concordant with recent reports that suggest a shared familial risk (inherited or environmental) for these hormone-dependent malignancies.

Examination of the effect of nongenetic risk factors on the familial risk of breast cancer among relatives of postmenopausal breast cancer patients

Relatives of postmenopausal breast cancer patients have a greater risk of breast cancer than do women with no family history of the disease. However, no study has previously examined the contribution of other breast cancer risk factors to risk in these relatives, thus precluding the ability to discern between shared environment or genes as the cause of familial aggregation. We conducted a nested case-control study of 251 index case families and 234 index control families. Incident breast cancer cases occurring in 1988-1989 and cancer-free controls were selected from a prospective cohort study. A pedigree development form was mailed to identify female relatives, who were then mailed a health history questionnaire. Index cases were significantly more likely than index controls to have at least one first-degree female relative with breast cancer [odds ratio = 1.62; 95% confidence interval = 1.03-2.54] after controlling for the total number of first-degree female relatives. After excluding the index cases and controls, logistic regression models were used to predict the odds of breast cancer in sisters (n = 72 cases). Sisters of index cases had slightly, although not statistically significant, elevated risk of both early-onset (age < 50 years; odds ratio = 1.34; 95% confidence interval = 0.54-3.30) and late-onset (age > or = 50 years; odds ratio = 1.56; 95% confidence interval = 0.87-2.79) breast cancer. Adjustment for nongenetic risk factors increased the odds ratio to 1.41 and 1.81, respectively. These data suggest that risk to sisters of postmenopausal breast cancer cases may be increased for both early- and late-onset breast cancer and this risk is apparently independent of measured risk factors.

Familial aggregation and heritability of waist-to-hip ratio in adult women: the Iowa Women's Health Study

The aim of this study was to assess evidence that genetic factors influence body fat distribution. First-degree relatives of 324 cancer-free females in a population-based prospective study of 41,837 women (99% white) between the ages of 55 and 69 at baseline in 1986 were studied. A total of 396 living sisters (mean age 65.7 years) and 446 living daughters (mean age 41.2 years) were identified through a mailed 'family tree' questionnaire sent to each participant. Family members were mailed a questionnaire to obtain self-reported measures of current height and weight. A paper tape measure and written instructions were enclosed to obtain waist and hip circumferences. The age-adjusted mother-daughters correlations for waist-to-hip ratio and body mass index (kg/m2) were 0.19 and 0.23, respectively (P < 0.05 using Fisher's z-transformation). The corresponding sister-sister correlations were 0.23 and 0.19, respectively (P < 0.05). The sister-sister correlations were not significantly different from the mother-daughter correlations. After adjustment for body mass index the mother-daughter correlation for waist-to-hip ratio increased to 0.20 and the sister-sister correlation increased to 0.26. These familial correlations suggest that genes and common environment may contribute 40 to 50% of the total variance of waist-to-hip ratio in white women in the Midwest.

Angiotensin I-converting enzyme (ACE): estimation of DNA haplotypes in unrelated individuals using denaturing gradient gel blots

The angiotensin I-converting enzyme (ACE) gene (17q23) is a candidate gene for essential hypertension and related diseases, but investigation of its role in human pathology is hampered by a lack of identified polymorphisms. Currently, a 287-bp insertion/deletion (I/D) RFLP in intron 16 represents the only one known. Additional polymorphisms for the ACE gene would make most families informative for linkage studies and would allow haplotypes to be assigned in association studies. To increase the information provided by the ACE gene, we used a sensitive screening technique, denaturing gradient gel electrophoresis (DGGE) blots, to identify polymorphisms and combined this with gene counting to identify haplotypes. Five independent polymorphisms, restriction fragment melting polymorphisms (RFMPs), were identified by four probes (encompassing half of the ACE cDNA) in digests produced by three restriction enzymes (DdeI, RsaI, and AluI). One RFMP has three alleles while the others have two alleles. In a sample of 67 unrelated control subjects, minor allele frequencies ranged from 0.12 to 0.49. A significant level of linkage disequilibrium was found for all pairs of markers. The four most informative RFMPs, taken in combination, define 24 potential haplotypes. Based on gene counting, 11 of the 24 are rare or nonexistent in this population, and the estimated heterozygosity of the remaining 13 haplotypes approaches 80%. Under these conditions for the ACE locus, phase-unknown genotypes could be assigned to haplotype pairs in unrelated subjects with reasonable certainty. Thus, using DGGE blot technique for identifying numerous DNA polymorphisms in a candidate locus, in combination with gene counting, one can often identify DNA haplotypes for both related and unrelated study subjects at a candidate locus. These markers in the ACE gene should be useful for clinical and epidemiologic studies of the role of ACE in human disease.

Leuprolide acetate for exhibitionism in Huntington's disease

We treated a patient with Huntington's disease and exhibitionism using leuprolide acetate (Lupron Depot, TAP Pharmaceuticals), a gonadotropin-releasing hormone agonist. The result was elimination of his deviant sexual behavior with few side effects. This regimen may be a safe and effective pharmacological treatment of the paraphilias. The occurrence of paraphilias in basal ganglia disorders is reviewed.

HLA-DQB1-associated susceptibility that distinguishes Hashimoto's thyroiditis from Graves' disease in type I diabetic patients

Insulin-dependent diabetes (IDDM) is frequently associated with autoimmune thyroid disease (ATD) within families. In these families, HLA polymorphism may modulate the susceptibility to each disease. Families with IDDM were further categorized as to the presence of ATD. IDDM-affected subjects from families without ATD were compared with subjects with ATD or with IDDM and ATD from IDDM/ATD families and with a control group. IDDM susceptibility in IDDM/ATD families was negatively associated with the presence of DQB1*0602 [relative risk (RR) = 0.038; P = 0.0001; corrected P (Pc) = 0.0005] and *0301 (RR = 0.3; P = 0.002; Pc = 0.01) and positively associated with the presence of DQB1*0201 (RR = 3.4; P = 0.0007; Pc = 0.0035) and *0302 (RR = 5; P = 0.0001; Pc = 0.0005), regardless of ATD. Compared with the IDDM-only group, the ATD-only group had an increased frequency of subjects with DQB1*0602 (RR = 0.14; P = 0.031), suggesting that the known IDDM-protective effect of this allele may be independent of susceptibility to ATD; however, this difference was not significant when the P value was correlated for the number of alleles tested. In these families, susceptibility to ATD was only associated with DQB1*0201 (RR = 5.71; P = 0.0043; Pc = 0.021). Among subjects with DQB1*0201, there was a weak negative association between the presence of DQB1*0302 on the second haplotype and Hashimoto's thyroiditis (RR = 0.237; P = 0.026; Pc > 0.05). We conclude that in IDDM/ATD families, IDDM-affected subjects are at risk for ATD, especially those carrying DQB1*0201. This risk may be influenced by the alleles carried on the second haplotype, with DQB1*0302 (or a closely linked gene) protecting from Hashimoto's thyroiditis and favoring Graves' disease.

Does body fat distribution promote familial aggregation of adult onset diabetes mellitus and postmenopausal breast cancer?

Noninsulin-dependent diabetes mellitus and postmenopausal breast cancer share a number of risk factors, including obesity, increased waist-to-hip ratio, and a positive family history. If risk for these diseases is mediated through a familial tendency for abdominal obesity, then one might expect to see familial clustering of both diseases. We analyzed data from a prospective cohort study of 41,837 Iowa women age 55-69 years. Diabetes was not associated with incidence of breast cancer [relative risk (RR) = 0.97]. The association between family history of breast cancer and breast cancer incidence, however, was slightly modified by individual history of diabetes: a positive family history of breast cancer in the absence of baseline diabetes was associated with a relative risk of 1.36 [95% confidence interval (CI) = 1.08-1.70], whereas the presence of both factors was associated with a RR of 1.87 (95% CI = 0.93-3.76). Adjustment for waist-to-hip ratio greatly diminished this difference. Conversely, a family history of breast cancer was associated with a RR of 5-year diabetes mortality of 1.94 (95% CI = 1.17-3.24) that persisted after stratification by tertile of waist-to-hip ratio. No clear association of family history of breast cancer and waist-to-hip ratio for self-reported diabetes incidence was evident. These data are indicative of a complex interrelation between waist-to-hip ratio, familial predisposition, diabetes, and breast cancer.

Frequent HLA class I and DP sequence mismatches in serologically (HLA-A, HLA-B, HLA-DR) and molecularly (HLA-DRB1, HLA-DQA1, HLA-DQB1) HLA-identical unrelated bone marrow transplant pairs

The rates of graft-versus-host disease (GVHD) and rejection are significantly higher among recipients of unrelated donor marrow (BM) than in recipients of marrow from HLA-identical siblings, even when donors and recipients are mixed lymphocyte culture (MLC) compatible and serologically and Dw identical. It has been hypothesized that phenotypically silent HLA class I and DP sequence mismatches might be associated with these differences, but little is known about their incidence. We have sequenced the HLA-A, HLA-B, HLA-C, HLA-DPA1, and HLA-DPB1 genes expressed by 12 unrelated marrow transplant pairs, 11 of whom were molecularly matched at DRB, DQA1, and DQB1 loci. Nine of these pairs were also HLA-A and HLA-B matched by serology. Six of these nine "HLA-identical" pairs were HLA-A (2 of 6), HLA-B (1 of 6), and HLA-C (6 of 6) mismatched at the sequence level. The mismatched class I alleles of all these pairs had strikingly different sequence motifs in the six specificity pockets of their antigen recognition site, and in five pairs they also had sequence differences at positions implicated in T-cell receptor (TCR) binding. Two of the three pairs who were serologically mismatched for one HLA-A or HLA-B antigen were also sequence mismatched at HLA-C. Finally, 10 of 11 pairs tested expressed different DP sequences. These data indicate that HLA class I, especially HLA-C, and DP sequence mismatches are frequent among unrelated subjects defined as HLA identical by current typing methods. We speculate that these sequence differences may explain, at least in part, the higher incidence of acute GVHD and rejection in unrelated BM transplantation as opposed to transplantation between HLA-identical siblings. Because of their high frequency, the role of HLA-A, HLA-B, HLA-C, and HLA-DP mismatches in transplantation outcome is now amenable to direct study.

Inflammatory and immune responses are impaired in mice deficient in intercellular adhesion molecule 1

Gene targeting was used to produce mice deficient in intercellular adhesion molecule 1 (ICAM-1) or CD54, an immunoglobulin-like cell adhesion molecule that binds beta 2 integrins. Homozygous deficient animals develop normally, are fertile, and have a moderate granulocytosis. The nature of the mutation, RNA analysis, and immunostaining are consistent with complete loss of surface expression of ICAM-1. Deficient mice exhibit prominent abnormalities of inflammatory responses including impaired neutrophil emigration in response to chemical peritonitis and decreased contact hypersensitivity to 2,4-dinitrofluorobenzene. Mutant cells provided negligible stimulation in the mixed lymphocyte reaction, although they proliferated normally as responder cells. These mutant animals will be extremely valuable for examining the role of ICAM-1 and its counterreceptors in inflammatory disease processes and atherosclerosis.

Cross-validation of protein structural class prediction using statistical clustering and neural networks

We present an approach to predicting protein structural class that uses amino acid composition and hydrophobic pattern frequency information as input to two types of neural networks: (1) a three-layer back-propagation network and (2) a learning vector quantization network. The results of these methods are compared to those obtained from a modified Euclidean statistical clustering algorithm. The protein sequence data used to drive these algorithms consist of the normalized frequency of up to 20 amino acid types and six hydrophobic amino acid patterns. From these frequency values the structural class predictions for each protein (all-alpha, all-beta, or alpha-beta classes) are derived. Examples consisting of 64 previously classified proteins were randomly divided into multiple training (56 proteins) and test (8 proteins) sets. The best performing algorithm on the test sets was the learning vector quantization network using 17 inputs, obtaining a prediction accuracy of 80.2%. The Matthews correlation coefficients are statistically significant for all algorithms and all structural classes. The differences between algorithms are in general not statistically significant. These results show that information exists in protein primary sequences that is easily obtainable and useful for the prediction of protein structural class by neural networks as well as by standard statistical clustering algorithms.

HLA class I sequence-based typing

HLA oligogenotyping has been used successfully to characterize most phenotypically undetectable variants of class II genes. Limitations inherent to the class I system have, however, complicated the application of this and other molecular approaches to HLA class I typing. We have previously shown that HLA class II polymorphism can be analyzed by a SBT approach. Here we present a class I-SBT strategy that provides complete sequence information for the two most polymorphic exons of the HLA-A, -B, and -C alleles. HLA class I SBT is based on direct sequencing of PCR-amplified HLA-A, -B, and -C cDNAs and requires a total of six cDNA -PCR-sequencing reactions (two per locus) and 13 different oligonucleotides. Each combination of oligonucleotides per reaction results in locus-specific sequence ladders and allows identification of both alleles in heterozygotes. Application of HLA-A, HLA-B, and HLA-C SBT to 26 homozygous and 32 serologically heterozygous samples has resulted in the identification of 24 novel class I nucleotide sequences encoding 17 new major histocompatibility complex class I products. An unexpected high degree of heterogeneity was found at the HLA-C locus with 14 novel sequences. Although there was a good correlation between the serologic phenotypes and SBT results, HLA-C SBT of most HLA-C serologically homozygous samples (heterozygous for HLA-A and/or -B) revealed heterozygozity (six of eight). SBT, the first molecular typing approach that has been generalized to both class I and class II genes, may be of special interest in applications demanding high sensitivity and specificity, such as in paternity testing or in the evaluation of the effects of sequence allelism in the outcome of unrelated bone marrow transplantation.

HLA-associated susceptibility to type 2 (non-insulin-dependent) diabetes mellitus: the Wadena City Health Study

Epidemiologic data suggest that a parental history of Type 2 (non-insulin-dependent) diabetes mellitus increases the risk of Type 1 (insulin-dependent) diabetes in siblings of a Type 1 diabetes proband. This increase in risk is consistent with a shared genetic susceptibility between Type 1 and Type 2 diabetes. We have previously reported evidence that HLA-DR4-linked factors may represent a homogeneous subset of diabetes susceptibility. First, HLA-DR4 frequency was higher in Type 1 diabetic study subjects with a Type 2 diabetic parent than in Type 1 diabetic subjects whose parents were not diabetic. Second, a DR4-haplotype was transmitted from the Type 2 diabetic parent to the Type 1 offspring more often than expected. These data are consistent with the hypothesis that families with a Type 2 diabetic parent and Type 1 diabetic child, heavily determined by HLA-DR4 linked factors, may represent a homogeneous subset of diabetes susceptibility. In this report, we further explore the relationship between the high-risk HLA antigen (HLA-DR4) in study subjects with differing glycaemic status (National Diabetes Data Group criteria). In this community-based study, we find evidence that HLA-DR4 is increased in study subjects with Type 2 diabetes and may be a marker for Type 2 diabetes susceptibility.

Homozygous parent affected sib pair method for detecting disease predisposing variants: application to insulin dependent diabetes mellitus

For complex genetic diseases involving incomplete penetrance, genetic heterogeneity, and multiple disease genes, it is often difficult to determine the molecular variant(s) responsible for the disease pathogenesis. Linkage and association studies may help identify genetic regions and molecular variants suspected of being directly responsible for disease predisposition or protection, but, especially for complex diseases, they are less useful for determining when a predisposing molecular variant has been identified. In this paper, we expand upon the simple concept that if a genetic factor predisposing to disease has been fully identified, then a parent homozygous for this factor should transmit either of his/her copies at random to any affected children. Closely linked markers are used to determine identity by descent values in affected sib pairs from a parent homozygous for a putative disease predisposing factor. The expected deviation of haplotype sharing from 50%, when not all haplotypes carrying this factor are in fact equally predisposing, has been algebraically determined for a single locus general disease model. Equations to determine expected sharing for multiple disease alleles or multiple disease locus models have been formulated. The recessive case is in practice limiting and therefore can be used to estimate the maximum proportion of putative susceptibility haplotypes which are in fact predisposing to disease when the mode of inheritance of a disease is unknown. This method has been applied to 27 DR3/DR3 parents and 50 DR4/DR4 parents who have at least 2 children affected with insulin dependent diabetes mellitus (IDDM). The transmission of both DR3 and DR4 haplotypes is statistically different from 50% (P < 0.05 and P < 0.001, respectively). An upper estimate for the proportion of DR3 haplotypes associated with a high IDDM susceptibility is 49%, and for DR4 haplotypes 38%. Our results show that the joint presence of non-Asp at DQ beta position 57 and Arg at DQ alpha position 52, which has been proposed as a strong IDDM predisposing factor, is insufficient to explain the HLA component of IDDM predisposition.

Familial clustering of colon, breast, uterine, and ovarian cancers as assessed by family history

The aggregation of colon, endometrial, ovarian, and possibly breast cancers in families has been described as a "cancer family syndrome" (now called Lynch syndrome II). To determine if the familial clustering of these malignancies was more common in women with cancer than without, we analyzed data from the Iowa Women's Health Study (IWHS), a population-based sample of 41,837 women aged 55-69 years. Self-reported information was collected on history of colon, uterine, ovarian, and breast cancers in female first-degree relatives. A family history of cancer of the breast (odds ratio [OR] = 1.4), colon (OR = 1.3), and uterus (OR = 1.3), but not ovary (OR = 1.2), was significantly more common among women with a personal history of any of these four cancers (all P < 0.05); the pattern of the ORs suggested strongly that the clustering tended to be site-specific. Age-adjusted relative risks (RR) of incident colon cancer over 5 years of follow-up (N = 237) were calculated with regard to family history. Colon cancer incidence was increased among women with a family history of breast (RR = 1.3), uterine (RR = 1.4), colon (RR = 1.5), and ovarian (RR = 1.3) cancers, although none of the risk estimates achieved statistical significance. RR was, however, significantly related to the number of different cancer sites reported among family members (Ptrend = 0.008). These data on a representative sample of postmenopausal women suggest that family histories of colon, breast, uterine, and ovarian cancers are associated with an increased risk of cancer at the same site, but provide little support for the hypothesis that Lynch syndrome II is a non-random occurrence.

Genetic analysis of atopy in three large kindreds: no evidence of linkage to D11S97

Both genetic and environmental influences have been implicated in the pathogenesis of atopic disease. A recent report suggested that a major gene providing susceptibility to atopy was transmitted in a pattern consistent with autosomal dominant inheritance and evidence was presented that places the disease locus near the D11S97 marker on human chromosome 11q. In this report, we present three large, highly characterized pedigrees in which atopy is transmitted in a pattern consistent with autosomal dominant inheritance. Genotypes at the D11S97 and HLA loci were evaluated using both lod score and sib pair methods of analysis. In these pedigrees, we reject close moderate linkage (up to 10 cM) of atopy with both D11S97 and HLA.

Familial clustering of insulin sensitivity

This study's objective was to determine whether there is familial clustering of insulin sensitivity (SI) or insulin-independent glucose uptake (SG), which would be evidence that they are genetically determined traits. Outpatients had a 3-h intravenous glucose tolerance test. Nondiabetic individuals (n = 183), ranging in age from 16 to 60 yr, were from 105 families that had 2 parents with non-insulin-dependent diabetes mellitus. Of these families, 62 contributed 1 offspring, 21 contributed 2, 13 contributed 3, 6 contributed 4, and 2 and 1 contributed 5 and 6, respectively. The minimal model of glucose disposal and the glucose and insulin values from the intravenous glucose tolerance tests were used to estimate SI and SG. The intraclass correlation coefficient was used to compare the within-family variability of SI and SG with the respective between-family distributions. The intraclass correlation coefficients were 0.26 (P = 0.008) for SI and 0.081 (P = 0.45) for SG. SI and SG were uncorrelated (r = -0.059, P = 0.42). The intraclass correlation of SI could not be explained by familial clustering of fasting insulin or ideal body weight. Finally, the 10 families with the lowest values of SI had a significantly higher within-sibship variability of SI than the other 33 families (P less than 0.001, F test). SI but not SG showed familial clustering, which is consistent with a polygenic determinant of SI. In addition, a large within-family variability of SI in some families is compatible with a major gene effect with a dominant mode of inheritance.(ABSTRACT TRUNCATED AT 250 WORDS)

Lung cancer detection and prevention: evidence for an interaction between smoking and genetic predisposition

The initiation and promotion of cancer is thought to result from a series of genetic mutations, some of which may be inherited. Our analysis of 337 lung cancer families suggested that, after allowing for an individual's pack-years of tobacco use, the pattern of disease was best explained by Mendelian codominant inheritance of an allele that produced earlier age of onset. Since lung cancer rarely occurs in the absence of exposure to tobacco, differences in the prevalence of smoking across generations could have a profound influence on the fit of genetic models. In the present study, families were partitioned into two groups, based on the birth cohort of the proband, i.e., born before World War I (age at death, greater than or equal to 60 years) or born after World War I (age at death, less than 60 years). This partition was chosen because the year 1915 signaled the start of the dramatic rise in tobacco use in the United States. In younger proband families, in which parents were more likely to smoke, Mendelian codominant inheritance provided the best fit to the data. In older proband families, for whom smoking among parents was less prevalent, the "no major gene" and "environmental" hypotheses were rejected; however, no Mendelian models could be distinguished. If the results on the families with the most homogeneous exposure to tobacco across generations (born after World War I) reflect the true underlying biology, then the influence of genetic factors in the pathogenesis of lung has been underestimated; the cumulative probability of lung cancer at age 80 for a noncarrier of the gene, at the average level of tobacco consumption, is close to zero, implying that virtually all lung cancer occurs among gene carriers. Identification of this putative genetic factor has profound implications for the detection and prevention of lung cancer.

Autosomal dominant spinocerebellar ataxia: locus heterogeneity in a Nebraska kindred

SCA1 is an adult-onset autosomal dominant ataxia that is genetically linked to loci on chromosome 6p. A highly informative GT-repeat marker, D6S89, has been closely linked to the SCA1 locus in five large kindreds. We have used this marker to perform linkage analysis in a smaller autosomal dominant ataxia family consisting of five generations designated as the Nebraska kindred. This kindred includes 33 affected (12 living) and 40 first-generation at-risk individuals. We examined eight affected individuals; all had gait and limb ataxia. We analyzed the D6S89 locus by the polymerase chain reaction. Based on the analysis of 31 individuals from this kindred, we statistically excluded linkage to D6S89 for moderate-to-tight linkage (less than 11% recombination). These data clearly demonstrate genetic heterogeneity among the autosomal dominant ataxias. In addition, we obtained linkage data for HLA-A and SCA1 in this kindred. Comparison of HLA-A with D6S89 shows the latter marker to be more powerful. Use of D6S89 and other highly polymorphic markers in this region will greatly facilitate genetic classification of ataxias and make presymptomatic diagnosis of SCA1 feasible.

HLA class II "typing": direct sequencing of DRB, DQB, and DQA genes

Routine clinical HLA class II typing is based largely on serological and cellular methods. These methods have many drawbacks that have led to the evaluation of molecular approaches to typing, including restriction fragment length polymorphism studies and oligotyping. We present here an alternative molecular approach, sequence-based typing (SBT), that allows direct determination of the sequences of all HLA class II polymorphic genes, thus providing the most detailed information currently possible in this regard. The data presented here using SBT are based on direct sequencing of polymerase chain reaction (PCR)-amplified DRB, DQB, and DQA cDNAs using a limited number of oligonucleotides. The oligonucleotides are designed to allow simultaneous determination of allelic sequences in any heterozygote as well as characterization of DRB isotypic complexity. Two types of amplification oligonucleotides (nonconserved and/or conserved) are used for DRB typing, which involves a maximum of four simultaneous cDNA/PCR/sequencing reactions. The first of these reactions only uses conserved oligonucleotides and is designed to detect all the different DRB transcripts present in any given heterozygote; the other three reactions use nonconserved oligonucleotides and are designed to ensure the unambiguous interpretation of the most complex DRB heterozygote combinations. Characterization of DQA1 and DQB1 sequences can be performed by using conserved oligonucleotides and only involves one reaction per locus. We have applied SBT to 43 homozygous cell lines and to 38 different heterozygote combinations that had previously been serologically typed. In all cases we were able to determine the allelic composition at DRB1, DRB3/4/5 and/or DQB1, and DQA1 loci of these cell lines and subjects; our results, analyzed by blind protocol, were consistent with the serological phenotypes. SBT can be extended to class I and class III genes and is automatable. We believe that this strategy deserves further evaluation as a possible HLA typing method.

Effect of cohort differences in smoking prevalence on models of lung cancer susceptibility

Data on 337 lung cancer families were analyzed to determine if known cohort differences in parental cigarette consumption influence parameters from a segregation analysis. Previous results suggested that, after allowing for an individual's pack-years of tobacco exposure, Mendelian codominant inheritance of an allele that produced an earlier age of onset provided a good fit to the data. In the present study, the data were split into two groups of families: probands age 60 and over (born before WWI) and probands younger than age 60. This partition of the data by age of the proband was done to separate families in which there were parents who were less likely to smoke from those with parents more likely to smoke--predicated on the known increase of smoking prevalence after World War I. For the younger proband families (those with parents more likely to smoke), only Mendelian codominant inheritance adequately fit the data. The hypotheses of no major type, environmental transmission, and Mendelian dominant or recessive inheritance were rejected. In contrast to our earlier findings, the estimate of population susceptibility increased from 28% in the total data to 60% in this subset. In the older proband families (those with parents less likely to smoke), the no major type and environmental hypotheses were rejected; further, none of the Mendelian models could be distinguished. Our results demonstrate that cohort differences, probably in exposure to tobacco, can confound parameters of a segregation analysis, and suggest that the genetic component of lung cancer may be greater than previously estimated. It further suggests that susceptibility to lung cancer occurs as a function of susceptibility to the effects of tobacco smoking.

Protocol for genetic testing in Huntington disease: three years of experience in Minnesota

Molecular genetic testing for Huntington disease (HD) by linkage analysis of DNA markers close to the HD gene has been possible since the mid-1980s. Because of ethical and practical concerns about this kind of testing, most groups performing the test in the past have operated under lengthy research protocols designed to assess the psychological morbidity of the presymptomatic diagnosis of a fatal disease. Our approach to HD testing is service-oriented, and our testing process has been designed to be flexible, to meet the varying needs of our patients. Between 1988 and 1990, 87 inquiries about the test have been received; 22 inquiries had family structures which were unsuitable for linkage analysis. Eleven of the 37 individuals who entered the testing program have not completed it. Of 19 patients who have received DNA results, seven received an increased risk of carrying the HD gene, and ten, a decreased risk. For two additional individuals, nonpaternity resulted in a negligible risk for HD. Several of those consulted, or their spouses, have had continuing outpatient counseling since completing the test; none have required hospitalization. Our short-term results indicate that molecular genetic testing for HD can be performed safely in a clinical setting using our protocol. As molecular genetic testing for HD and other diseases moves out of research centers and into clinics, clinicians must devise practical strategies for providing the medical, genetic, and psychological services needed for the growing number of individuals who will seek such testing.

Familial aggregation of nasopharyngeal carcinoma and other malignancies. A clinicopathologic description

Nasopharyngeal carcinoma (NPC) occurred in five members in three generations of a white American family of Scandinavian descent. Six other family members had malignancies including malignant melanoma, malignant lymphoma, squamous cell carcinoma of the tongue, adenocarcinoma of the colon, and asynchronous bilateral in situ and invasive ductal carcinomas of the breast. There was also a history of autoimmune disorders and exposure to smoke, fumes, and chemicals in some family members. Regression analysis revealed a significant covariate risk for exposure to smoking, alcohol ingestion, dust, salted or spicy foods, and poorly ventilated conditions. According to segregation analysis, the susceptibility to nasopharyngeal carcinoma and other malignancies in this family was transmitted as an autosomal codominant characteristic. A specific histocompatibility antigen (HLA) haplotype of A1-B37-DR6 was associated with a predisposition for NPC, but no linkage was identified. Laboratory studies in selected family members did not reveal significantly elevated levels of Epstein-Barr virus antibodies or serum carcinoembryonic antigen. No specific karyotypic abnormalities were identified with peripheral blood chromosome analysis. This family was an example of apparent autosomal codominant susceptibility to NPC and other malignancies. The relationship of malignancy to the HLA haplotype of A1-B37-DR6, autoimmune disorders, and cytogenetic abnormalities was intriguing but not defined clearly.