A brief note on the resemblance between relatives in the presence of population stratification

Population stratification occurs when a study population is comprised of several sub-populations, and can result in increased false positive findings in genomewide-association studies. Recently published work shows that sub-population-specific positive assortative mating at the genotypic level results in population stratification. We show that if the allele frequency of a single nucleotide polymorphism responsible for a trait varies between sub-populations and there is no dominance variance, then the heritability of the trait increases, primarily due to an increase in the additive genetic variance of the trait.

Cystic fibrosis mutations for p.F508del compound heterozygotes predict sweat chloride levels and pancreatic sufficiency

Cystic fibrosis (CF) is a monogenetic disease with a complex phenotype. Over 1500 mutations in the CFTR gene have been identified; however, the p.F508del mutation is most common. There has been limited correlation between the CFTR mutation genotype and the disease phenotypes. We evaluated the non-p.F508del mutation of 108 p.F508del compound heterozygotes using the biological classification method, Grantham and Sorting Intolerant from Tolerant (SIFT) scores to assess whether these scoring systems correlated with sweat chloride levels, pancreatic sufficiency, predicted FEV(1) , and risk of infection with Pseudomonas aeruginosa in the last year. Mutations predicted to be 'mild' by the biological classification method are associated with more normal sweat chloride levels (p < 0.001), pancreatic sufficiency (p < 0.001) and decreased risk of infection with Pseudomonas in the last year (p = 0.014). Lower Grantham scores are associated with more normal sweat chloride levels (p < 0.001), and pancreatic sufficiency (p = 0.014). Higher SIFT scores are associated with more normal sweat chloride levels (p < 0.001) and pancreatic sufficiency (p = 0.011). There was no association between pulmonary function measured by predicted FEV(1) and the biological classification (p = 0.98), Grantham (p = 0.28) or SIFT scores (p = 0.62), which suggests the pulmonary disease related to CF may involve other modifier genes and environmental factors.

Increased risk for recurrent major depression in DYT1 dystonia mutation carriers

BACKGROUND

Prior studies suggest that dystonia is comorbid with affective disorders. This comorbidity could be a reaction to a chronic debilitating disorder or expression of a predisposing gene. The authors took advantage of the identification of a gene for dystonia, DYT1, to test these alternative explanations.

METHODS

The authors administered a standardized psychiatric interview to members of families with an identified DYT1 mutation. The authors classified family members into three groups: mutation carriers with dystonia (manifesting carriers; n = 96), mutation carriers without dystonia (non-manifesting carriers; n = 60), and noncarriers (n = 65).

RESULTS

The risk for recurrent major depressive disorder was increased in both non-manifesting carriers (RR = 4.95, CI = 1.72 to 14.29) and manifesting carriers (RR = 3.62, CI = 1.00 to 10.53) compared with noncarriers. Mutation carriers also had earlier age at onset of recurrent major depressive disorder than noncarriers. The severity of motor signs was not associated with the likelihood of recurrent depression. Mutation carriers did not have an increased risk for other affective disorders, such as single major depression or bipolar disorder.

CONCLUSIONS

Early-onset recurrent major depression is associated with the DYT1 GAG mutation and this association is independent of motor manifestations of dystonia. These findings suggest that early-onset recurrent depression is a clinical expression of the DYT1 gene mutation.

Twin concordance and sibling recurrence rates in multiple sclerosis

Size and ascertainment constraints often limit twin studies to concordance comparisons between identical and fraternal twins. Here we report the final results of a longitudinal, population-based study of twins with multiple sclerosis (MS) in Canada. Bias was demonstrably minimized, and an estimated 75% of all Canadian MS twin pairs were ascertained, giving a sample sufficiently large (n = 370) to permit additional informative comparisons. Twinning was not found to affect prevalence, and twins with MS did not differ from nontwins for DR15 allele frequency nor for MS risk to their siblings. Probandwise concordance rates of 25.3% (SE +/- 4.4) for monozygotic (MZ), 5.4% (+/-2.8) for dizygotic (DZ), and 2.9% (+/-0.6) for their nontwin siblings were found. MZ twin concordance was in excess of DZ twin concordance. The excess concordance in MZ was derived primarily from like-sexed female pairs with a probandwise concordance rate of 34 of 100 (34 +/- 5.7%) compared with 3 of 79 (3.8 +/- 2.8%) for female DZ pairs. We did not demonstrate an MZ/DZ difference in males, although the sample size was small. We observed a 2-fold increase in risk to DZ twins over nontwin siblings of twins, but the difference was not significant.

Myoclonus dystonia: possible association with obsessive-compulsive disorder and alcohol dependence

BACKGROUND

Inherited myoclonus-dystonia (M-D) is a disorder that is characterized primarily by myoclonic jerks and is often accompanied by dystonia. In addition to motor features, psychiatric disease is reported in some families.

METHODS

To determine whether the same genetic etiology underlies both neurologic and psychiatric signs, the authors studied psychiatric symptoms in nonmanifesting carriers (NMC), noncarriers (NC), and manifesting carriers (MC) in three families demonstrating linkage of M-D to the 7q21 locus. Interviewers administered the computerized version of the Composite International Diagnostic Interview. Algorithms for the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition diagnosis of obsessive-compulsive disorder (OCD), generalized anxiety disorder, major affective disorder, alcohol abuse, alcohol dependence, drug abuse, and drug dependence were used. Rates of disorders among the MC, NMC, and NC were compared.

RESULTS

Of 55 participating individuals, 16 were MC, 11 were NMC, and 28 were NC. The rate of OCD was greater in carriers (5/27) compared with NC (0/28) (p = 0.023). It was also greater in the symptomatic gene carriers (4/16) compared with the asymptomatic group (1/11) (p = 0.022). Alcohol dependence was increased in the symptomatic carriers (7/16) (p = 0.027), but not in the carrier group overall (7/27).

CONCLUSION

OCD may be associated with the DYT11 M-D gene; however, a larger sample is necessary to confirm this finding. Alcohol dependence is highly associated with expressing symptoms of M-D. This may be explained by self-medication with alcohol to improve motor symptoms of M-D.

Searching for genetic determinants in the new millennium

Human genetics is now at a critical juncture. The molecular methods used successfully to identify the genes underlying rare mendelian syndromes are failing to find the numerous genes causing more common, familial, non-mendelian diseases. With the human genome sequence nearing completion, new opportunities are being presented for unravelling the complex genetic basis of non-mendelian disorders based on large-scale genome-wide studies. Considerable debate has arisen regarding the best approach to take. In this review I discuss these issues, together with suggestions for optimal post-genome strategies.

The DYT1 phenotype and guidelines for diagnostic testing

OBJECTIVE

To develop diagnostic testing guidelines for the DYT1 GAG deletion in the Ashkenazi Jewish (AJ) and non-Jewish (NJ) primary torsion dystonia (PTD) populations and to determine the range of dystonic features in affected DYT1 deletion carriers.

METHODS

The authors screened 267 individuals with PTD; 170 were clinically ascertained for diagnosis and treatment, 87 were affected family members ascertained for genetic studies, and 10 were clinically and genetically ascertained and included in both groups. We used published primers and PCR amplification across the critical DYT1 region to determine GAG deletion status. Features of dystonia in clinically ascertained (affected) DYT1 GAG deletion carriers and noncarriers were compared to determine a classification scheme that optimized prediction of carriers. The authors assessed the range of clinical features in the genetically ascertained (affected) DYT1 deletion carriers and tested for differences between AJ and NJ patients.

RESULTS

The optimal algorithm for classification of clinically ascertained carriers was disease onset before age 24 years in a limb (misclassification, 16.5%; sensitivity, 95%; specificity, 80%). Although application of this classification scheme provided good separation in the AJ group (sensitivity, 96%; specificity, 88%), as well as in the group overall, it was less specific in discriminating NJ carriers from noncarriers (sensitivity, 94%; specificity, 69%). Using age 26 years as the cut-off and any site at onset gave a sensitivity of 100%, but specificity decreased to 54% (63% in AJ and 43% in NJ). Among genetically ascertained carriers, onset up to age 44 years occurred, although the great majority displayed early limb onset. There were no significant differences between AJ and NJ genetically ascertained carriers, except that a higher proportion of NJ carriers had onset in a leg, rather than an arm, and widespread disease.

CONCLUSIONS

Diagnostic DYT1 testing in conjunction with genetic counseling is recommended for patients with PTD with onset before age 26 years, as this single criterion detected 100% of clinically ascertained carriers, with specificities of 43% to 63%. Testing patients with onset after age 26 years also may be warranted in those having an affected relative with early onset, as the only carriers we observed with onset at age 26 or later were genetically ascertained relatives of individuals whose symptoms started before age 26 years.

Postnatal experiences and genetic effects on squirrel monkey social affinities and emotional distress

Most nonhuman primate research on risk factors underlying vulnerability to stress has focused on early psychosocial experiences in various species of macaques. To test for genetic and experiential effects on emotional vulnerability in randomly bred squirrel monkeys, here we combined a paternal half-sibling analysis with three postnatal rearing protocols that altered aspects of maternal availability. In one condition offspring were periodically removed from natal groups, whereas differences in maternal availability were produced in two other conditions by manipulating the effort required of lactating mothers to successfully locate food. After completion of these protocols at 21 weeks of age, social affinities, maternal separation induced peep-calls, and plasma levels of cortisol were assessed from 29 to 37 weeks of age. Significant postnatal rearing effects and the lowest heritabilities were detected in peak elevations of cortisol measured 1 day after the removal of mothers from otherwise undisturbed groups. Individual differences in cortisol 3-7 days later revealed negligible postnatal rearing effects and the highest heritabilities (h(2) approximately. 70), as offspring sired by certain fathers failed to return to the preseparation level found in undisturbed natal groups. Paternal half-siblings that responded with long lasting increases in cortisol spent more time near their mother in undisturbed groups and exhibited long-lasting increases in separation induced peep-calls. These findings concur with human twin studies that suggest genetic and experiential factors contribute to individual differences in vulnerability to emotional distress.

Search for the PARK3 founder haplotype in a large cohort of patients with Parkinson's disease from northern Germany

A founder haplotype on chromosome 2p for autosomal dominant Parkinson's disease (PD) has been postulated for two families of Northern European descent, and a new mutation in the alpha-synuclein gene (Ala30Pro) has been found in a German PD family. We evaluated 85 German PD patients and 85 ethnically matched controls for shared markers on chromosome 2p and for the new alpha-synuclein mutation. We found no evidence for linkage disequilibrium, suggesting that the putative founder mutation on chromosome 2p is not a common cause of PD in the local population. Furthermore, no patient carried the Ala30Pro change, supporting earlier findings that mutations in the alpha-synuclein gene are extremely rare.

Search for a founder mutation in idiopathic focal dystonia from Northern Germany

Both the discovery of the DYT1 gene on chromosome 9q34 in autosomal dominant early-onset torsion dystonia and the detection of linkage for one form of adult-onset focal dystonia to chromosome 18p (DYT7) in a family from northern Germany provide the opportunity to further investigate genetic factors in the focal dystonias. Additionally, reports of linkage disequilibrium between several chromosome 18 markers and focal dystonia, both in sporadic patients from northern Germany and in members of affected families from central Europe suggest the existence of a founder mutation underlying focal dystonia in this population. To evaluate the role of these loci in focal dystonia, we tested 85 patients from northern Germany who had primary focal dystonia, both for the GAG deletion in the DYT1 gene on chromosome 9q34 and for linkage disequilibrium at the chromosome 18p markers D18S1105, D18S1098, D18S481, and D18S54. None of these patients had the GAG deletion in the DYT1 gene. Furthermore, Hardy-Weinberg analysis of markers on 18p in our patient population and in 85 control subjects from the same region did not support linkage disequilibrium. Taken together, these results suggest that most cases of focal dystonia in patients of northern German or central European origin are due neither to the GAG deletion in DYT1 nor to a proposed founder mutation on chromosome 18p but must be caused by other genetic or environmental factors.

Canadian collaborative project on genetic susceptibility to MS, phase 2: rationale and method. Canadian Collaborative Study Group

BACKGROUND

Results from the Canadian Collaborative Project on Genetic Susceptibility to Multiple Sclerosis (MS)-Phase 1 (CCPGSMS-Phase 1) together with other family data published since 1982 have led to the following conclusions about the etiology of MS: (i) genetic and non-genetic (environmental) factors are involved in the etiology of MS on a population basis; (ii) the familial aggregation of MS is genetic; (iii) maternal factors do not influence the risk for siblings to develop MS; and (iv) MS appears to be oligogenic. The present paper describes the rationale and methodology for the CCPGSMS-Phase 2.

METHOD

The CCPGSMS-Phase 2 is a nation-wide collaborative effort involving all the 15 Canadian MS clinics. A series of structured questionnaires is administered to MS index cases, spouse controls and mothers of index cases and spouse controls (if available) by trained interviewers. Blood samples are taken for molecular genetic studies. This national effort is coordinated by the MS Clinics in Vancouver and London.

RESULTS

The CCPGSMS-Phase 2 is in progress so specific results are not available. The study is designed to (i) increase the database for genetic epidemiological/molecular genetic research and (ii) gather population-based data to further our understanding of the non-genetic factors in the etiology of MS.

CONCLUSIONS

It is anticipated that the results from this study will impact on the eventual prevention, cure and treatment of MS.

De novo mutations (GAG deletion) in the DYT1 gene in two non-Jewish patients with early-onset dystonia

The DYT1 gene recently has been cloned and shown to contain a three nucleotide (GAG) deletion responsible for most cases of autosomal dominant early-onset torsion dystonia. This deletion results in the loss of one of a pair of glutamic acids in a conserved region of a novel ATP-binding protein (torsinA). Previous haplotype analysis revealed that this same deletion had arisen at least two different times in history, suggesting independent mutational events. This deletion is the only sequence change found thus far to be associated uniquely with the disease status, regardless of ethnic origin. Here we describe two patients with typical early-onset torsion dystonia of Swiss-Mennonite and non-Jewish Russian origin, respectively, that both carry this same mutation as a de novo GAG deletion. This finding proves that this 3 bp deletion in the DYT1 gene is indeed a mutation that causes early-onset torsion dystonia. The DYT1 mutation is one of the rare examples of the same recurrent mutation causing a dominantly inherited condition. The sequence surrounding the GAG deletion contains an imperfect 24 bp tandem repeat, suggesting a possible mechanism for the high frequency of this mutation.

Effect of age at onset and parental disease status on sibling risks for MS

MS is believed to be a complex trait determined by genetic and nongenetic factors. Data suggest that MS susceptibility and age at onset are each, at least to some extent, under genetic control. The present study carefully examined five covariates (sex of the index case, sex of the sibling, birth cohort of the sibling [< or = 1919, 1920 to 1939, > or = 1940], age of MS onset in the index patient (< or = 20 years, 21 to 30 years, 31 to 40 years, > 40 years), and MS disease status of the parents [i.e., MS present in one parent or no parent with MS]) that may influence the familial risk of MS in a large cohort of 1,896 MS patients and 8,878 of their first-degree relatives. Of these, sex of the sibling, parental MS status, and index patient onset age were the important factors influencing MS risks to siblings. The results of this study are (1) the index-patient-onset-age effect suggests that individuals with a greater genetic loading (i.e., a greater contribution of susceptibility alleles) have an earlier age at onset and (2) genetic loading is substantially increased in individuals with an affected parent. These data are important both for genetic counseling and gene identification studies.

Idiopathic torsion dystonia linked to chromosome 8 in two Mennonite families

The DYT1 locus on chromosome 9q34 is responsible for most childhood limb-onset idiopathic torsion dystonia (ITD). Linkage to DYT1 has been excluded in families with adult-onset, and predominantly cranial-cervical, ITD. We mapped a locus (DYT6) associated with prominent cranial-cervical ITD in two large Mennonite families to chromosome 8. An identical haplotype spanning 40-cM segregates with ITD in these families, suggesting a shared mutation from the recent past.

The early-onset torsion dystonia gene (DYT1) encodes an ATP-binding protein

Early-onset torsion dystonia is a movement disorder, characterized by twisting muscle contractures, that begins in childhood. Symptoms are believed to result from altered neuronal communication in the basal ganglia. This study identifies the DYT1 gene on human chromosome 9q34 as being responsible for this dominant disease. Almost all cases of early-onset dystonia have a unique 3-bp deletion that appears to have arisen idependently in different ethnic populations. This deletion results in loss of one of a pair of glutamic-acid residues in a conserved region of a novel ATP-binding protein, termed torsinA. This protein has homologues in nematode, rat, mouse and humans, with some resemblance to the family of heat-shock proteins and Clp proteases.

Secondary dystonia and the DYTI gene

Early-onset (< 28 years) primary dystonia in most Ashkenazi Jews is due to a single founder mutation in the DYT1 gene on chromosome 9q34, as determined by very strong linkage disequilibrium with a haplotype of 9q34 alleles at surrounding marker loci. The role of this mutation in individuals with secondary causes for dystonia has never been tested, although environmental insults, such as neuroleptic exposure or perinatal asphyxia, are proposed to precipitate dystonia in genetically predisposed individuals. We assessed 9q34 haplotypes in 40 Ashkenazi patients with secondary dystonia; 25 had early onset of symptoms, including 15 with exposure to neuroleptic medication or perinatal asphyxia. Of the 25 patients with early onset, 9 were considered phenocopies of DYT1 having normal examinations except for dystonia, normal radiographic and other laboratory studies, and onset in a limb or the neck. Only one individual whose dystonia developed in the setting of a measles infection carried the associated haplotype. Our findings indicate that clinical diagnostic criteria that include historical information to detect tardive dystonia and perinatal asphyxia discriminate primary dystonia due to the DYT1 founder mutation. We found no evidence that the DYT1 founder mutation contributes to secondary dystonia.

Exclusion of the DYT1 locus in familial torticollis

Clinical-genetic studies of idiopathic torsion dystonia (ITD) indicate that the DYT1 gene on chromosome 9q34 is responsible for most childhood limb-onset disease. The genetic basis of adult-onset ITD is less well studied. In most multiplex adult-onset ITD families, dystonia is limited to the cervical, cranial, or brachial muscles; in a few rare families, dystonia also involves the legs and trunk. Previous linkage studies have excluded the DYT1 locus in these atypical families. We studied two large non-Jewish families with adult-onset ITD limited to the cervical and brachial muscles and excluded the DYT1-containing region. This study further restricts the role of DYT1 to childhood limb-onset ITD and suggests that other genes are responsible for focal adult-onset ITD.

A novel MHC class I-like gene is mutated in patients with hereditary haemochromatosis

Hereditary haemochromatosis (HH), which affects some 1 in 400 and has an estimated carrier frequency of 1 in 10 individuals of Northern European descent, results in multi-organ dysfunction caused by increased iron deposition, and is treatable if detected early. Using linkage-disequilibrium and full haplotype analysis, we have identified a 250-kilobase region more than 3 megabases telomeric of the major histocompatibility complex (MHC) that is identical-by-descent in 85% of patient chromosomes. Within this region, we have identified a gene related to the MHC class I family, termed HLA-H, containing two missense alterations. One of these is predicted to inactivate this class of proteins and was found homozygous in 83% of 178 patients. A role of this gene in haemochromatosis is supported by the frequency and nature of the major mutation and prior studies implicating MHC class I-like proteins in iron metabolism.

Evidence for genetic basis of multiple sclerosis. The Canadian Collaborative Study Group

BACKGROUND Increased familial risks in multiple sclerosis (MS) range from 300-fold for monozygotic twins to 20-40-fold for biological first-degree relatives, suggesting a genetic influence. Yet if one identical twin has MS the other usually will not. One way of sorting out the contributions of genes and environment is to study half-sibs. METHODS In a Canadian population-based sample of 16 000 MS cases seen at 14 regional MS clinics one half-sib (or more) was reported by 939 index cases. By interview we elicited information on family structure and an illness in half-sibs and any full brothers or sisters. FINDINGS The age-adjusted MS rate in the 1839 half-sibs of these index cases was 1.32 percent compared with 3.46 percent for the 1395 full sibs of the same cases (p<0.001; likelihood ratio test). There were no significant differences in risk for maternal versus paternal half-sibs (1.42 percent vs 1.19 percent) or for those raised together versus those raised apart from the index case (1.17 percent vs 1.47 percent). INTERPRETATION Besides demonstrating the power and the feasibility of using half-sib studies to throw light on the aetiology of complex disorders, our findings show that a shared environment does not account for familial risk in MS and that maternal effects (such as intrauterine and perinatal factors, breastfeeding, and genomic imprinting) have no demonstrable effect on familial risk. Halving the number of potentially contributory genes (by comparing full-sib and half-sib rates) lowers the risk of MS by a factor of 2.62, an observation consistent with a polygenic hypothesis.

The genetic attributable risk of breast and ovarian cancer

BACKGROUND

The age-specific proportion of breast and ovarian cancer in the general population that is likely to be due to a breast/ovarian cancer susceptibility gene(s) is estimated. In addition, the age-specific penetrance of ovarian cancer for women predicted to be carriers of a susceptibility gene is calculated using population-based data.

METHODS

Data are from the Cancer and Steroid Hormone Study, a population-based, case-control study conducted by the Centers for Disease Control, which includes 4730 breast cancer cases aged 20 to 54 years. Information regarding the occurrence of breast and ovarian cancer was collected for mothers and sisters of the cases during an in-home interview. The probability of being a breast cancer susceptibility gene carrier was calculated for each of the breast cancer cases using information on the family history of breast cancer. The calculated risk of ovarian cancer in the first-degree relatives of breast cancer cases with a high probability of being a gene carrier is compared with that seen in first-degree relatives of breast cancer cases with a low probability of being a gene carrier and used to calculate the proportion of ovarian cancer cases that are likely to be due to a breast/ovarian susceptibility gene(s) as well as the age-specific risk of developing ovarian cancer for gene carriers.

RESULTS

Approximately 10% of ovarian cancer cases and 7% of breast cancer cases in the general population are estimated to be carriers of a breast/ovarian cancer susceptibility gene; these women are found primarily in families characterized by multiple cases of the early onset of breast cancer. The proportion of breast cancer cases predicted to be attributable to the gene decreases markedly with age; approximately 33% of cases age 20-29 years compared with approximately 2% of cases age 70-79 years. The proportion of ovarian cancer cases predicted to be due to the susceptibility gene ranges from 14% among patients diagnosed in their 30s to 7% among those diagnosed in their 50s. Carriers are predicted to have at least 15 times the age-specific risk of ovarian cancer of noncarriers. Among women predicted to carry the gene, the cumulative risk of developing ovarian cancer by the age of 59 years is approximately 10%.

CONCLUSIONS

The estimates provided may prove helpful to clinicians until such time as large-scale population-based screening for breast and ovarian cancer susceptibility genes is possible.

Mapping quantitative trait loci with extreme discordant sib pairs: sampling considerations

Elsewhere we have proposed the use of extreme discordant sib pairs (EDSPs) for mapping quantitative trait loci in humans. Here we present sample sizes necessary to achieve a given level of power with this study design, as well as the number of sibs that need to be screened to obtain the required sample. Further, we present simple formulas for adjusting sample sizes to account for variable significance levels and power, as well as the density and informativeness of linkage markers in a multipoint sib-pair analysis. We conclude that with EDSPs, the most powerful study design, the smallest genetic effect detectable with a realistic sample size is approximately 10% of the variance of the trait.

A genetic basis for familial aggregation in multiple sclerosis. Canadian Collaborative Study Group

Genetic-environmental interactions probably underlie spontaneous human autoimmune disorders, a category of complex traits thought to include multiple sclerosis (MS). The geographical distribution and familial aggregation of this disease have often been ascribed to the role of infectious agents, but there is no consensus. Increased family risks range from 300-fold for monozygotic twins to 20-40-fold for biological first-degree relatives over the general population prevalence of 0.1% (ref. 6). We screened a population-based sample of 15,000 individuals with MS by using standardized, personally administered questionnaires to identify adopted index cases and/or those who had adopted relatives. The frequency of MS among first-degree non-biological relatives living with the index case was no greater than expected from Canadian population prevalence data and significantly less than for biological relatives. These findings indicate that familial aggregation of MS is genetically determined: no effect of shared environment was detectable.

Dystonia in Ashkenazi Jews: clinical characterization of a founder mutation

A gene (DYT1) for idiopathic torsion dystonia maps to chromosome 9q34 in Ashkenazi Jewish families with early onset of symptoms. Further, there is linkage disequilibrium between DYT1 and a particular haplotype of alleles at 9q34 loci in this population. This implies that a large proportion of early-onset idiopathic torsion dystonia in Ashkenazi Jews is due to a founder mutation in DYT1. To characterize the phenotypic range of this mutation, we studied 174 Ashkenazi Jewish individuals affected with idiopathic torsion dystonia. We used GT(n) markers on chromosome 9q34 (D9S62, D9S63, and ASS) and classified individuals as having ("carriers"), not having ("noncarriers"), or being ambiguous with respect to a DYT1-associated haplotype. We assessed clinical features and found marked clinical differences between haplotype carriers and noncarriers. There were 90 carriers, 70 noncarriers, and 14 ambiguous individuals. The mean age at onset of symptoms was significantly lower in carriers than in noncarriers (12.5 +/- 8.2 vs 36.5 +/- 16.4 years). In 94% of carriers, symptoms began in a limb (arm or leg equally); rarely the disorder started in the neck (3.3%) or larynx (2.2%). In contrast, the neck, larynx, and other cranial muscles were the sites of onset in 79% of noncarriers; onset in the arms occurred in 21% and onset in the legs never occurred. Limb onset, leg involvement in the course of disease, and age at onset distinguished haplotype carriers from noncarriers with 90% accuracy. In conclusion, there are clinical differences between Ashkenazi Jewish individuals with idiopathic torsion dystonia who do or do not have a unique DYT1 mutation, as determined by a DYT1-associated haplotype of 9q34 alleles.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective effect of apolipoprotein E type 2 allele for late onset Alzheimer disease

Gene dosage of the apolipoprotein E (APOE) epsilon 4 allele is a major risk factor for familial Alzheimer disease (AD) of late onset (after age 60). Here we studied a large series of 115 AD case subjects and 243 controls as well as 150 affected and 197 unaffected members of 66 AD families. Our data demonstrate a protective effect of the epsilon 2 allele, in addition to the dose effect of the epsilon 4 allele in sporadic AD. Although a substantial proportion (65%) of AD is attributable to the presence of epsilon 4 alleles, risk of AD is lowest in subjects with the epsilon 2/epsilon 3 genotype, with an additional 23% of AD attributable to the absence of an epsilon 2 allele. The opposite actions of the epsilon 2 and epsilon 4 alleles further support the direct involvement of APOE in the pathogenesis of AD.

Comorbidity and co-transmission of alcoholism, anxiety and depression

This paper applies data from a family study of depression to assess patterns of comorbidity and co-transmission of alcoholism, anxiety disorder, and major depression. We found that all three disorders were strongly transmissible; however, alcoholism demonstrated the greatest degree of familial aggregation. The pairwise associations among depression, anxiety and alcoholism indicated that the traits are co-transmitted in families, especially depression and anxiety. Individual associations between traits (or comorbidity) were entirely explained by transmitted (perhaps genetic) agents, because the correlations between traits due to random environment were not significant. These findings have important implications for treatment, psychiatric nosology, and aetiological investigations of these conditions.

Linkage mapping of dopa-responsive dystonia (DRD) to chromosome 14q

Dopa-responsive dystonia (DRD) is an autosomal-dominant neurological disorder which appears to result from a genetically determined deficiency of striatal dopamine. Pathological evidence suggests that this may be due to the establishment of a reduced number of dopaminergic nerve terminals in the striatum, or to an excessive reduction (pruning) of these terminals in early development. We have mapped the DRD gene to chromosome 14 by linkage analysis in 3 families with a maximum 2-point lod score of 4.67 at 8.6 centiMorgans from D14S63; maximum multipoint lod scores > 6 were obtained for the intervals D14S47-D14S52 and D14S52-D14S63. The flanking loci D14S47 and D14S63 define a region of about 22 cM as containing the DRD gene.

On the probability of matching DNA fingerprints

Forensic scientists commonly assume that DNA fingerprint patterns are infrequent in the general population and that genotypes are independent across loci. To test these assumptions, the number of matching DNA patterns in two large databases from the Federal Bureau of Investigation (FBI) and from Lifecodes was determined. No deviation from independence across loci in either database was apparent. For the Lifecodes database, the probability of a three-locus match ranges from 1 in 6,233 in Caucasians to 1 in 119,889 in Blacks. When considering all trios of five loci in the FBI database, there was only a single match observed out of more than 7.6 million comparisons. If independence is assumed, the probability of a five-locus match ranged from 1.32 x 10(-12) in Southeast Hispanics to 5.59 x 10(-14) in Blacks, implying that the minimum number of possible patterns for each ethnic group is several orders of magnitude greater than their corresponding population sizes in the United States. The most common five-locus pattern can have a frequency no greater than about 10(-6). Hence, individual five-locus DNA profiles are extremely uncommon, if not unique.

Sensitivity of chromosomal mosaicism detection by different tissue culture methods

In the field of prenatal cytogenetic diagnosis, two tissue culture methodologies are currently in use: the flask method, which examines mixed populations of cells, and the in situ method, which examines distinct colonies of cells. These two methods provide inherently different levels of sensitivity which can be made comparable by adjusting the number of cells examined depending on the methodology used and the number of colonies formed per ml of specimen. Assuming that there are 2 colonies per ml of amniotic fluid in a 20 ml specimen, in order to detect 10, 20, and 30 per cent mosaicism with 95 per cent confidence, 29, 14, and 9 colonies should be examined respectively by the in situ method. Similarly, 50, 17, and 10 cells must be analysed by the flask method.

Age at onset as an indicator of familial risk of breast cancer

The familial risk of breast cancer was investigated in a large population-based, case-control study conducted by the Centers for Disease Control. The data set included 4,730 histologically confirmed breast cancer cases aged 20-54 years and 4,688 controls who were frequency matched to cases by geographic region and 5-year categories of age. Family history of breast cancer among first-degree female relatives of cases and controls was utilized. To identify factors associated with familial risk of breast cancer, a Cox proportional hazards model was used, modeling time to onset of breast cancer among mothers and sisters. Case relatives were at greater risk than control relatives. Among relatives of cases, a significant increase in the risk of breast cancer was associated with decreasing age at onset of the case and with having an additional relative affected with breast cancer. The hazard ratio for the mother of a case with breast cancer diagnosed at 50 years of age was 1.7 (95% confidence interval (Cl) 1.4-2.0), compared with 2.7 (95% Cl 2.2-3.2) and 4.3 (95% Cl 3.3-5.6) for the mother of a case whose diagnosis occurred at 40 and 30 years of age, respectively. The hazard ratio for the sister of a case with an unaffected mother and at least one affected sister in addition to the case was 3.6 (95% Cl 2.1-6.1) when the case was diagnosed at age 50, compared with 5.8 (95% Cl 3.4-10.0) and 9.4 (95% Cl 5.3-16.7) when the case was diagnosed at 40 and 30 years of age, respectively. The hazard ratio for the sister of a case with an affected mother and no additional affected sisters was 5.9 (95% Cl 3.9-8.9) when the case was diagnosed at age 50, compared with 9.4 (95% Cl 6.2-14.4) and 15.1 (95% Cl 9.4-24.3) when the case was diagnosed at 40 and 30 years of age, respectively. The hazard ratio for the sister of a case with both an affected mother and at least one affected sister aside from the case was 17.1 (95% Cl 9.4-31.3) when the case was diagnosed at age 50, compared with 27.5 (95% Cl 15.0-50.3) and 44.2 (95% Cl 23.5-83.2) when the case was diagnosed at 40 and 30 years of age, respectively. No effect of case's menopausal status and bilaterality was found, indicating that in addition to a positive family history, age at onset is the strongest indicator of a possible genetic subtype of breast cancer in these data.

Using age of onset to distinguish between subforms of breast cancer

Information on family history and age of onset of breast cancer is examined in an attempt to distinguish between postulated early and late onset forms of breast cancer and to estimate the familial correlation between any subforms that may exist. Data are taken from the Cancer and Steroid Hormone Study, a multicentre, population-based, case-control study conducted by the Centers for Disease Control (CDC). The data set includes 4730 histologically confirmed breast cancer cases aged 20-54 and 4688 controls who were frequency-matched to cases by geographic region and five-year categories of age. Data regarding family history of breast cancer for mothers and sisters of cases and controls are used in this analysis. The methods of Smith (1976) are modified to obtain maximum likelihood estimates of heritability and familial correlation using 35, 40, 45, and 50 years of age as the dividing point between early and late onset. The heritabilities for both the early and late onset forms decrease and approach one another in size with increasing age cutpoint, although the heritability for the early group is always greater than that for the late group. Irrespective of cutpoint, the familial correlation between the two groups does not differ significantly from one, providing evidence for a single genetic form of breast cancer with familial cases increasingly represented among cases with earlier onset.

Segregation analysis of idiopathic torsion dystonia in Ashkenazi Jews suggests autosomal dominant inheritance

The results of segregation analysis applied to a family study of idiopathic torsion dystonia in Ashkenazi Jews are reported. The study is based on 43 probands (with age at onset prior to 27 years) from 42 nuclear families; pedigrees were extended systematically through all available first- and second-degree relatives, who were directly examined and videotaped. Final diagnoses were based on exam information and blinded videotape review. Segregation analysis demonstrated that the data are consistent with autosomal dominant inheritance with 30% penetrance. Recessive and polygenic inheritance were strongly rejected. There was no evidence for sporadic cases or new mutations. The high incidence and dominant inheritance of early-onset idiopathic torsion dystonia in Ashkenazi Jews suggests genetic homogeneity within this population, making it especially useful for linkage studies of this disorder.

The Continuous Performance Test, identical pairs version (CPT-IP): I. New findings about sustained attention in normal families

Thirty families, consisting of two parents and two adolescent children, were tested on a high-processing load Continuous Performance Test, the CPT-IP, which required identification of identical stimulus pairs within a continuously presented series of stimuli. The purpose of this study was to provide normative data for research concerned with the role of attention in psychopathology, especially schizophrenia and major affective disorder. Retest data collected from 23 of the 30 families showed the CPT-IP to be a reliable measure of attention. A major developmental effect was found in capacity to sustain attention to spatial vs. verbal stimuli, which suggested that spatial skills are most developed during childhood and adolescence, while verbal attentional skills tend to peak in adulthood. Factor analysis and family transmission patterns further suggested that the two types of attention (spatial and verbal) were independent and that each was heritable to some degree. Experimental distraction did not disrupt performance in any of the subjects and, in fact, tended to improve it in the adolescents, especially for spatial stimuli. We conclude that the CPT-IP is appropriate for use with families containing members differing widely in age and processing skills.

Migraine and depression: association and familial transmission

We have studied the association between migraine and major depression in a group of 133 probands with major depression, a group of 82 normal community controls and 400 interviewed first-degree relatives of the probands and controls. There was a significant association between depression and migraine among both the probands and the relatives. We also found that concomitant symptoms of anxiety were prominent among the depressed persons with migraine. Both depression and migraine were strongly familial but their association did not appear to be highly transmissible. Rather, our data suggested that depression may either be a sequela of migraine or the diathesis which results in both migraine and depression.