Kate Berg

Attention-Deficit/Hyperactivity Disorder in a Population Isolate: Linkage to Loci at 4q13.2, 5q33.3, 11q22, and 17p11

Attention-deficit/hyperactivity disorder (ADHD [MIM 143465]) is the most common behavioral disorder of childhood. Twin, adoption, segregation, association, and linkage studies have confirmed that genetics plays a major role in conferring susceptibility to ADHD. We applied model-based and model-free linkage analyses, as well as the pedigree disequilibrium test, to the results of a genomewide scan of extended and multigenerational families with ADHD from a genetic isolate. In these families, ADHD is highly comorbid with conduct and oppositional defiant disorders, as well as with alcohol and tobacco dependence. We found evidence of linkage to markers at chromosomes 4q13.2, 5q33.3, 8q11.23, 11q22, and 17p11 in individual families. Fine mapping applied to these regions resulted in significant linkage in the combined families at chromosomes 4q13.2 (two-point allele-sharing LOD score from LODPAL = 4.44 at D4S3248), 5q33.3 (two-point allele-sharing LOD score from LODPAL = 8.22 at D5S490), 11q22 (two-point allele-sharing LOD score from LODPAL = 5.77 at D11S1998; multipoint nonparametric linkage [NPL]-log[P value] = 5.49 at approximately 128 cM), and 17p11 (multipoint NPL-log [P value] >12 at approximately 12 cM; multipoint maximum location score 2.48 [alpha = 0.10] at approximately 12 cM; two-point allele-sharing LOD score from LODPAL = 3.73 at D17S1159). Additionally, suggestive linkage was found at chromosome 8q11.23 (combined two-point NPL-log [P value] >3.0 at D8S2332). Several of these regions are novel (4q13.2, 5q33.3, and 8q11.23), whereas others replicate already-published loci (11q22 and 17p11). The concordance between results from different analytical methods of linkage and the replication of data between two independent studies suggest that these loci truly harbor ADHD susceptibility genes.

A common variant of the latrophilin 3 gene, LPHN3, confers susceptibility to ADHD and predicts effectiveness of stimulant medication

Attention-Deficit/Hyperactivity Disorder (ADHD) has a very high heritability (0.8), suggesting that about 80% of phenotypic variance is due to genetic factors. We used the integration of statistical and functional approaches to discover a novel gene that contributes to ADHD. For our statistical approach, we started with a linkage study based on large multigenerational families in a population isolate, followed by fine mapping of targeted regions using a family-based design. Family- and population-based association studies in five samples from disparate regions of the world were used for replication. Brain imaging studies were performed to evaluate gene function. The linkage study discovered a genome region harbored in the Latrophilin 3 gene (LPHN3). In the world-wide samples (total n=6360, with 2627 ADHD cases and 2531 controls) statistical association of LPHN3 and ADHD was confirmed. Functional studies revealed that LPHN3 variants are expressed in key brain regions related to attention and activity, affect metabolism in neural circuits implicated in ADHD, and are associated with response to stimulant medication. Linkage and replicated association of ADHD with a novel non-candidate gene (LPHN3) provide new insights into the genetics, neurobiology, and treatment of ADHD.

Recruitment Experience in the First Phase of the African American Hereditary Prostate Cancer (AAHPC) Study

The African American Hereditary Prostate Cancer (AAHPC) Study is an ongoing multicenter genetic linkage study organized by Howard University and the National Human Genome Research Institute (NHGRI), with support from the Office for Research on Minority Health and the National Cancer Institute. The goals of the study are to: (i) look for evidence of involvement of chromosome 1q24-25 (HPC1) in African American men with hereditary prostate cancer (HPC) and (ii) conduct a genome-wide search for other loci associated with HPC in African American men. To accomplish these goals, a network has been established including Howard University, the NHGRI, and six Collaborative Recruitment Centers (CRCs). The CRCs are responsible for the identification and enrollment of 100 African American families. To date, 43 families have been enrolled. Recruitment strategies have included mass media campaigns, physician referrals, community health-fairs/prostate cancer screenings, support groups, tumor registries, as well as visits to churches, barber shops, and universities. By far, the most productive recruitment mechanisms have been physician referrals and tumor registries, yielding a total of 35 (81%) families. Approximately 41% (n = 3400) of probands initially contacted by phone or mail expressed interest in participating; the families of 2% of these met the eligibility criteria, and 75% of those families have been enrolled in the study, indicating a 0.5% recruitment yield (ratio of participants to contacts). As the first large-scale genetic linkage study of African Americans, on a common disease, the challenges and successes of the recruitment process for the AAHPC Study should serve to inform future efforts to involve this population in similar studies.

Diagnostic accuracy and confusability analyses: an application to the Diagnostic Interview for Genetic Studies

The dominant, contemporary paradigm for developing and refining diagnoses relies heavily on assessing reliability with kappa coefficients and virtually ignores a core component of psychometric practice: the theory of latent structures. This article describes a psychometric approach to psychiatric nosology that emphasizes the diagnostic accuracy and confusability of diagnostic categories. We apply these methods to the Diagnostic Interview for Genetic Studies (DIGS), a structured psychiatric interview designed by the NIMH Genetics Initiative for genetic studies of schizophrenia and bipolar disorder. Our results show that sensitivity and specificity were excellent for both DSM-III-R and RDC diagnoses of major depression, bipolar disorder, and schizophrenia. In contrast, diagnostic accuracy was substantially lower for subtypes of schizoaffective disorder-especially for the DSM-III-R definitions. Both the bipolar and depressed subtypes of DSM-III-R schizoaffective disorder had excellent specificity but poor sensitivity. The RDC definitions also had excellent specificity but were more sensitive than the DSM-III-R schizoaffective diagnoses. The source of low sensitivity for schizoaffective subtypes differed for the two diagnostic systems. For RDC criteria, the schizoaffective subtypes were frequently confused with one another; they were less frequently confused with other diagnoses. In contrast, the DSM-III-R subtypes were often confused with schizophrenia, but not with each other.

Attention-Deficit/Hyperactivity Disorder and Comorbid Disruptive Behavior Disorders: Evidence of Pleiotropy and New Susceptibility Loci

BACKGROUND Attention-deficit/hyperactivity disorder (ADHD) comorbid with oppositional defiant disorder (ODD) or conduct disorder (CD) and substance abuse/dependence seems to represent a specific subset within the phenotypic ADHD spectrum. METHODS We applied complex segregation and linkage analyses in a set of multigenerational families densely segregating ADHD comorbid with ODD, CD, alcohol abuse/dependence, and nicotine dependence. RESULTS Our data suggest that ADHD cosegregates with disruptive behaviors as a unique, phenotypically variable trait as evidenced by highly significant pair-wise linkages among: ADHD and ODD (logarithm of odds [LOD]=14.19), ADHD and CD (LOD=5.34), ODD and CD (LOD=6.68), and CD and alcohol abuse/dependence (LOD=3.98). In addition to previously reported ADHD susceptibility loci, we found evidence of linkage for comorbid ADHD phenotypes to loci at 8q24, 2p21-22.3, 5p13.1-p13.3, 12p11.23-13.3, 8q15, and 14q21.1-22.2. These results were replicated with an affected status phenotype derived from latent class clusters. CONCLUSIONS Patterns of cosegregation of ADHD with comorbidities can inform our understanding of the inheritance patterns not only of ADHD but also of disruptive behavioral disorders and alcohol abuse/dependence. Refining the comorbid ADHD phenotype by determining the cosegregation profile of specific comorbidities might be a powerful tool for defining significant regions of linkage.

Latent Class Subtyping of Attention-Deficit/Hyperactivity Disorder and Comorbid Conditions

OBJECTIVE Genetic studies of attention-deficit/hyperactivity disorder (ADHD) generally use discrete DSM-IV subtypes to define diagnostic status. To improve correspondence between phenotypic variance and putative susceptibility genes, multivariate classification methods such as latent class analysis (LCA) have been proposed. The aim of this study was to perform LCA in a sample of 1,010 individuals from a nationwide recruitment of unilineal nuclear families with at least one child with ADHD and another child either affected or clearly unaffected. METHOD LCA models containing one through 10 classes were fitted to data derived from all DSM-IV symptoms for ADHD, oppositional defiant disorder, and conduct disorder (CD), as well as seven items that screen for anxiety and depression from the National Initiative for Childrens Healthcare Quality Vanderbilt Assessment Scale for Parents. RESULTS We replicated six to eight statistically significantly distinct clusters, similar to those described in other cross-cultural studies, mostly stable when comorbidities are included. For all age groups, anxiety and depression are strongly related to Inattentive and Combined types. Externalizing symptoms, especially CD, are strongly associated with the Combined type of ADHD. Oppositional defiant disorder symptoms in young children are associated with either conduct disorder or anxiety-related symptoms. CONCLUSIONS Methods such as LCA allow inclusion of information about comorbidities to be quantitatively incorporated into genetic studies. LCA also permits incorporation of milder but still impairing phenotypes than are allowed using the DSM-IV. Such methods may be essential for analyses of large multicenter datasets and relevant for future clinical classifications. This population-based ADHD classification may help resolve the contradictory results presented in molecular genetic studies.

Pedigree disequilibrium test (PDT) replicates association and linkage between DRD4 and ADHD in multigenerational and extended pedigrees from a genetic isolate.

Association/linkage between dopamine D4 receptor (DRD4) polymorphisms and attention-deficit/hyperactivity disorder (ADHD) has been suggested by case–control- and nuclear-family-based studies. Here, we present a candidate gene analysis for DRD4 using 14 extended and multigenerational families segregating ADHD derived from the ‘Paisa’ community of Antioquia, Colombia, a genetic isolate. Two DRD4 polymorphisms (a 120 bp tandem duplication at the promoter and a 48 bp-VNTR at exon 3), reported associated to ADHD, were genotyped. Parametric and non-parametric linkage analyses, and a family-based association test (FBAT), the pedigree disequilibrium test (PDT), were applied to search for evidence of association/linkage. Two-point LOD scores were significantly negative, with values ranging from −3.21 (P=0.011158) to −7.66 (P=0.000091 at θ=0). Non-parametrical analysis resulted in nonsignificant evidence for linkage. The PDT showed a moderate trend toward significance of association/linkage between the 7-repeat (7R) allele at the 48 bp VNTR and ADHD (P=0.0578). Furthermore, the haplotype analysis shows a significant association/linkage of the 7R-240 bp haplotype (P=0.0467) with ADHD. Results suggest that either a moderate DRD4 genetic effect, or linkage disequilibrium of DRD4 with an ADHD disease locus in the vicinity or the linkage to a phenotypic component of the ADHD spectrum could be underlying this association/linkage. These results provide further evidence for the association of ADHD to genetic variation in or near to DRD4 and replicate the previously reported association between ADHD and the 7R allele.

In Search of Susceptibility Genes for Type 2 Diabetes in West Africa: The Design and Results of the First Phase of the AADM Study

PURPOSE The purpose of this study is to map type 2 diabetes susceptibility genes in West African ancestral populations of African-Americans, through an international collaboration between West African and US investigators. DESIGN AND METHODS Affected sib-pairs (ASP) along with unaffected spouse controls are being enrolled and examined in West Africa, with two sites established in Ghana (Accra and Kumasi) and three in Nigeria (Enugu, Ibadan, and Lagos). Eligible participants are invited to study clinics to obtain detailed epidemiologic, family, and medical history information. Blood samples are drawn from each participant to measure glucose, insulin, C-peptide, total cholesterol, LDL, HDL, triglycerides, albumin, creatinine, urea, uric acid, total calcium and to detect autoantibodies to glutamic acid decarboxylase (GAD). DNA is isolated from frozen white blood cells obtained from 20 ml of EDTA whole blood samples. RESULTS With full informed consent, 162 individuals from 78 families have been enrolled and examined since the Africa America Diabetes Mellitus (AADM) study began in June of 1997. Logistics of field examinations and specimen shipping have been successfully established. At the end of the third year of field activity (September 2000) the AADM study will have enrolled and performed comprehensive examination on 400 ASP with type 2 diabetes, for a minimum of 800 cases and 200 controls from Ghana and Nigeria. At the current participation rate, the goal of 400 sib-pairs and 200 controls will be met before the scheduled closing date. CONCLUSIONS The AADM study will create a comprehensive epidemiologic and genetic resource that will facilitate a powerful genome-wide search for West African susceptibility genes to type 2 diabetes.

Attention-deficit/hyperactivity disorder (ADHD): feasibility of linkage analysis in a genetic isolate using extended and multigenerational pedigrees

Segregation analyses converge in explaining the predisposition to attention‐deficit/hyperactivity disorder (ADHD) as the consequence of a major gene and exclude purely environmental or cultural transmission. As a result of the ADHD phenotype restrictions, collection of extended families or design of linkage studies using families has been extremely difficult and thus currently linkage studies have been performed using only concordant or discordant sib‐pairs rather than large families. On the other hand, intergenerational studies are represented by the transmission disequilibrium test (TDT) using trios. We collected pedigree data on ADHD from the Paisa community from Antioquia, Colombia, a genetic isolate. The goal of this study was to genetically map a putative gene predisposing to ADHD in a set of 27 multigenerational Paisa families. Here we present the results of a power simulation using SIMLINK to detect linkage of ADHD. ADHD was assumed to be a dichotomous trait with incomplete penetrance and a phenocopy rate of 3% in males and 0.2% in females. We simulated cosegregation of the trait and a marker locus in our pedigrees. We assumed Hardy–Weinberg and linkage equilibrium, equally frequent marker alleles and evaluated power at several recombination fractions between the trait and marker loci. Also, the ADHD trait was assumed to be genetically heterogeneous and different functions of age‐dependent penetrance were simulated. We found exceptionally good power to detect linkage (expected LOD > 14 if theta is 0.1 or less), and that the presence of heterogeneity up to 50% does not affect substantially the projected LOD scores even for a theta recombination value of 0.05 (eLOD > 5.87). Having now obtained blood samples and confirmatory interviews in five families (representing 20% of the projected number of families), we performed a new analysis. The expected mean LOD in these five families reached values close to 10 and remained invariant when heterogeneity and different penetrance models were considered. We discuss the relative benefits of using extended and multigenerational families for genetic mapping studies as opposed to using nuclear families, affected sib pairs or sporadic cases which require the collection of over 1000 analytical units to get the same power exhibited by the small number of pedigrees described here.

Clinical characteristics of African-American men with heriditary prostate cancer: The AAHPC study

Introduction: The African-American Hereditary Prostate Cancer (AAHPC) Study was designed to recruit African-American families fulfilling very stringent criteria of four or more members diagnosed with prostate cancer at a combined age at diagnosis of 65 years or less. This report describes the clinical characteristics of a sample of affected AAHPC family members.Methods: In all, 92 African-American families were recruited into the study between 1998 and 2002. Complete clinical data including age and PSA at diagnosis, number of affected per family, stage, grade, and primary treatment were available on 154 affected males. Nonparametric Wilcoxon two-sample tests and Fishers exact test (two-tailed), were performed to compare families with 4–6 and >6 affected males with respect to clinical characteristics.Results: The mean number of affected men per family was 5.5, with a mean age at diagnosis of 61.0 (±8.4) years. Age at diagnosis, PSA and Gleason score did not show significant differences between the two groups of families. Based on the Gleason score, 77.2% of affected males had favorable histology. Significantly, there were marked differences between the two groups in the frequency of node-positive disease (P=0.01) and distant metastases (P=0.0001). Radical prostatectomy was the preferred primary therapy for 66.2% of all affected men followed by 20.8% who chose radiation therapy.Conclusions: Our findings suggest that affected males who carry the highest load of genetic factors are at the highest risk for early dissemination of disease, thus efforts at early diagnosis and aggressive therapeutic approaches may be warranted in these families. Since the primary therapy choices in our study favored definitive treatment (87.0%) when compared to the 1983 and 1995 SEER data in which 28 and 64% received definitive treatment, respectively, it appears that affected African-American men in multiplex families may be demonstrating the reported psycho-social impact of family history on screening practices and treatment decisions for prostate cancer.