Analysis of Financial Barriers Experienced by Prospective Genetic Counseling Students.

PURPOSE: High costs of applying to genetic counseling graduate programs (GCGPs) are likely a barrier to workforce diversification. We sought to determine application costs and assess differences between individuals of historically underrepresented racial and ethnic backgrounds in medicine (hURM) and non-hURM applicants. METHODS: Applicants to GCGPs between 2005-2020 were surveyed about application history, related expenses, volunteer hours, and financial resources; 383 responses were analyzed. RESULTS: Median total application costs (MTAC) were $2,634, $4,762, and $5,607 (one, two, and three or more application cycles, respectively). Interview-related items (which includes travel) had the highest median cost (one application cycle: $879). Among those who applied to multiple cycles, hURM respondents had higher MTAC than those of non-hURM ($6,713 versus $4,762, p=0.03) and lower median total volunteer hours (246 versus 381, p=0.03). Parental education level differed by hURM status (p=0.04). Median financial contribution from parents with and without advanced degrees varied significantly (60% vs 2%, p=0.0009). CONCLUSION: Significant costs are incurred during the GCGP application process, but notable differences in costs and resources were observed between hURM and non-hURM applicants. Stakeholders within the profession should implement strategies to reduce financial barriers and the resulting inequities in the application process.

Dopamine genes and ADHD.

Family, twin, and adoption studies have documented a strong genetic basis for ADHD/HKD, but these studies do not identify specific genes linked to the disorder. Molecular genetic studies can identify allelic variations of specific genes that are functionally associated with ADHD/HKD, and dopamine genes have been the initial candidates based on the site of action of the stimulants drugs, which for a half century have provided the primary pharmacological treatment for ADHD/HKD. Two candidate dopamine genes have been investigated and reported to be associated with ADHD/HKD: the dopamine transporter (DAT1) gene [Cook et al., American Journal of Human Genetics 1995;56:993-998, Gill et al., Molecular Psychiatry 1997;2:311-313] and the dopamine receptor D4 (DRD4) gene [LaHoste et al., Molecular Psychiatry 1996;1:121-124: Smalley et al., 1998;3:427-430; Swanson et al., Molecular Psychiatry 1998;3:38-41]. Speculative hypotheses [Swanson and Castellanos, NIH Consensus Development Conference: Diagnosis and Treatment of Attention Deficit Hyperactivity Disorder, November 1998. p. 37-42] have suggested that specific alleles of these dopamine genes may alter dopamine transmission in the neural networks implicated in ADHD/HKD (e.g. that the 10-repeat allele of the DAT1 gene may be associated with hyperactive re-uptake of dopamine or that the 7-repeat allele of the DRD4 gene may be associated with a subsensitive postsynaptic receptor). These and other variants of the dopamine hypothesis of ADHD will be discussed.

A new betaA1-crystallin splice junction mutation in autosomal dominant cataract.

PURPOSE: To map the locus for autosomal dominant cataracts (ADCs) in a Brazilian family using candidate gene linkage analyses, describe the clinical variability, and identify potential mutations in the human betaA1-crystallin gene (CRYBA1), a candidate gene identified through linkage studies demonstrating cosegregation with markers on chromosome 17. METHODS: Members of a Brazilian family with ADC were studied. Clinical examinations and linkage analyses with polymerase chain reaction (PCR) polymorphisms of 22 anonymous markers and 2 within the neurofibromatosis type 1 gene were performed; two-point lod scores were calculated. DNA sequences of all 6 exons and 12 exon-intron boundaries of the betaA1-crystallin gene, a proximal candidate gene mapped to 17q11.1-q12 in one unaffected and two affected individuals, were screened and new variants assessed for cosegregation with the disease. RESULTS: Affected individuals exhibited variable expressivity of pulverulent opacities in the embryonal nucleus and sutures; star-shaped, shieldlike, or radial opacities in the posterior embryonal nucleus; and/or midcortical opacities. All known loci for ADC in this family on chromosomes 1 and 13 were excluded. A positive lod score on chromosome 17 was calculated. This ADC locus was mapped to two potential regions on the long arm with an intervening recombination. The only known candidate gene in these regions was betaA1-crystallin. Three previously unreported single nucleotide variants were found in this gene, one in the donor splice junction site of intron C. This variant was found in all affected members and is presumed to be the causative mutation. CONCLUSIONS: An ADC locus was mapped in a Brazilian family with variable expressivity to either 17q23.1-23.2 or 17q11.1-12 based on linkage analyses. Analyses of DNA sequences of the betaA1-crystallin gene in this family revealed three new variants, one of which is within a donor splice junction and cosegregates with affected members.

A new locus for autosomal dominant cataract on chromosome 12q13.

PURPOSE: To map the gene for autosomal dominant cataracts (ADC) in an American white family of European descent. METHODS: Ophthalmic examinations and linkage analyses using a variety of polymorphisms were performed; two-point lod scores calculated. RESULTS: Affected individuals (14 studied) exhibited variable expressivity of embryonal nuclear opacities based on morphology, location within the lens, and density. This ADC locus to 12q13 was mapped on the basis of statistically significantly positive lod scores and no recombinations (theta(m) = theta(f) = 0) with markers D12S368, D12S270, D12S96, D12S359, D12S1586, D12S312, D12S1632, D12S90, and D12S83; assuming full penetrance, a maximum lod score of 4.73 was calculated between the disease locus and D12S90. CONCLUSIONS: The disease in this family represents the first ADC locus on chromosome 12; major intrinsic protein of lens fiber (MIP) is a candidate gene.

HLA haplotypes, polysomnography, and pedigrees in a case series of patients with narcolepsy.

An ongoing study of the genetics of narcolepsy ascertains families through a case series of narcoleptic probands using diagnostic criteria consisting of 1) clinical history of excessive somnolence, 2) a mean sleep latency on the multiple sleep latency test (MSLT) of less than 7.9 minutes, 3) the rapid eye movement (REM) sleep-related symptom of cataplexy, 4) nocturnal polysomnography ruling out sleep apnea syndrome, and 5) two or more transitions to REM sleep on the MSLT. All probands and first-degree relatives received clinical and laboratory evaluations as well as human leukocyte antigen (HLA) typing. Demographic characteristics of the 32 probands are as follows: 17 males and 15 females; mean age was 42.1 years (range 13-70 years). The polysomnographic data confirmed daytime sleepiness and increased tendency for REM sleep for the 32 probands. Nocturnal polysomnographic results are as follows: sleep latency, 3.2 minutes; total sleep time, 442 minutes. MSLT results are as follows: sleep latency, 3.1 minutes; REM latency, 6.9 minutes; number of REM periods, 3.2. HLA typing revealed the presence of the HLA haplotypes, DRB1*15 and DQB1*0602, in 21 narcoleptic probands, with two African-Americans having the DQB1*0602 but not the DRB1*15 allele. Among the 57 relatives of the 32 probands, 1/31 females and 7/26 males were found to be affected with narcolepsy (p < 0.02), which suggests a higher diagnostic rate in male relatives. The 21 probands who were positive for the DRB1*15 and DQB1*0602 haplotypes did not differ from the 10 probands who were negative for these alleles in terms of their nocturnal sleep parameters, MSLT findings, or clinical presentation. Three families with multiple individuals affected with narcolepsy are presented. Two families have more than one affected individual who does not have the high-risk HLA haplotype. In one of these families, the disease is segregating independently of any HLA haplotype. In the third family, there is cosegregation with HLA DRB1*15 and DQB1*0602. One family contains a pair of DNA-confirmed, monozygotic twins with narcolepsy who are discordant for cataplexy and have the HLA DR14(Dw9)/DQB1*0503 and DR4(Dw4)/DQB1*0302 haplotypes.

Bipolar disorder: evidence for a major locus.

Complex segregation analyses were conducted on families of bipolar I and bipolar II probands to delineate the mode of inheritance. The probands were ascertained from consecutive referrals to the Mood Disorder Service, University Hospital, University of British Columbia and diagnosed by DSM-III-R and Research Diagnostic Criteria. Data were available on over 1,500 first-degree relatives of the 186 Caucasian probands. The purpose of the analyses was to determine if, after correcting for age and birth cohort, there was evidence for a single major locus. Five models were fit to the data using the statistical package SAGE: i) dominant, ii) recessive, iii) arbitrary mendelian inheritance, iv) environmental, and v) no major effects. A single dominant, mendelian major locus was the best fitting of these models for the sample of bipolar I and II probands when only bipolar relatives were defined as affected (polygenic inheritance could not be tested). Adding recurrent major depression to the diagnosis "affected" for relatives reduced the evidence for a major locus effect. Our findings support the undertaking of linkage studies and are consistent with the analyses of the National Institutes of Mental Health (NIMH) Collaborative Study data by Rice et al. (Arch Gen Psychiatry 44: 441-447, 1987) and Blangero and Elston (Genet Epidemiol 6:221-227, 1989).

Ultrasonographic detection of orbicularis oris defects in first degree relatives of isolated cleft lip patients.

The phenotypic variability of non-syndromic cleft lip (CL) is broad. We demonstrate that the prevalence of orbicularis oris (OO) muscle anomalies, detectable only by ultrasound, is higher in first-degree relatives of individuals with overt CL than in the general population. These findings suggest that occult OO defects may be part of the spectrum of the CL phenotype, that offspring of individuals with such defects are at an increased risk to develop overt CL, and that ultrasound may be a useful tool in future population studies designed to identify CL susceptibility genes.

Possible locus for bipolar disorder near the dopamine transporter on chromosome 5.

The dopamine transporter (DAT) plays a key role in the regulation of dopaminergic neurotransmission by mediating the active reuptake of synaptic dopamine. It is an important candidate gene for bipolar disorder because of data implicating dopamine abnormalities in mania, and because it is the site of action of amphetamine, which has activating and psychotogenic properties. DAT has recently been cloned by its homology to a family of transporters, and mapped to chromosome 5p15.3. We tested DAT for linkage to bipolar disorder in a collection of 21 families from the general North American population (University of California, San Diego/University of British Columbia [UCSD/UBC] families), three Icelandic pedigrees, and Old Order Amish pedigree 110. We examined three markers at DAT, including a 5' TaqI RFLP (HDAT-TaqI), a highly polymorphic variable number of tandem repeats marker (VNTR) (HDAT-VNTR1), and a 3' 40-bp repeat marker (HDAT-PCR1), as well as two nearby microsatellite markers, D5S392 and D5S406. A maximum lod score of 2.38 was obtained at D5S392 in one of the UCSD/UBC families under an autosomal-dominant model. A lod score of 1.09 was also obtained under the same dominant model in the Amish at HDAT-PCR1. In the combined set of families, a maximum lod score of 1.76 was obtained under an autosomal-recessive model at HDAT-TaqI. Positive results were also obtained at several markers, using three nonparametric methods in the UCSD/UBC family set: the affected pedigree member method (P = 0.001), an affected sib pair method (ESPA, P = 0.0008), and the transmission disequilibrium test (P = 0.024). These results suggest the presence of a susceptibility locus for bipolar disorder near the DAT locus on chromosome 5.

Genetic linkage study of bipolar disorder and the serotonin transporter.

The serotonin transporter (HTT) is an important candidate gene for the genetic transmission of bipolar disorder. It is the site of action of many antidepressants, and plays a key role in the regulation of serotonin neurotransmission. Many studies of affectively ill patients have found abnormalities in serotonin metabolism, and dysregulation of the transporter itself. The human serotonin transporter has been recently cloned and mapped to chromosome 17. We have identified a PstI RFLP at the HTT locus, and here report our examination of this polymorphism for possible linkage to bipolar disorder. Eighteen families were examined from three populations: the Old Order Amish, Iceland, and the general North American population. In addition to HTT, three other microsatellite markers were examined, which span an interval known to contain HTT. Linkage analyses were conducted under both dominant and recessive models, as well as both narrow (bipolar only) and broad (bipolar + recurrent unipolar) diagnostic models. Linkage could be excluded to HTT under all models examined. Linkage to the interval spanned by the microsatellites was similarly excluded under the dominant models. In two individual families, maximum lod scores of 1.02 and 0.84 were obtained at D17S798 and HTT, respectively. However, these data overall do not support the presence of a susceptibility locus for bipolar disorder near the serotonin transporter.

Genetic heterogeneity in tuberous sclerosis. Study of a large collaborative dataset.

Tuberous sclerosis (TSC) is a multisystem autosomal dominant hamartosis whose genetics is complicated by reduced penetrance and widely varying clinical expression. Results of linkage analyses have variously suggested two different locations for a TSC gene. A collaborative dataset has been assembled to clarify the issue of genetic heterogeneity. We have now analyzed the data from a combined sample of 111 families. Using Ott's HOMOG programs, we completed three tests of homogeneity: (1) for chromosome 9q, (2) for chromosome 11q, and (3) for the combined 9q and 11q data. For test 1 the chi-square (1 df) was 21.54 (p less than 0.001), for test 2 the chi-square (1 df) was 0.13 (p greater than 0.35), and for test 3 the chi-square (2 df) was 37.61 (p less than 0.0001). Additionally, we examined the combined data for evidence that a third, as yet unlinked locus exists. Results of this last test were suggestive but not significant. Clearly loci for TSC are present on both chromosomes 9q and 11q. The maximum likelihood estimate of the proportion of chromosome 9q-linked families is 0.38, for chromosome 11q-linked families is 0.47, and for the unlinked type 0.15. Alternative explanations for these latter families include chance sampling of recombinants, nongenetic phenocopies, or misclassification.

Evidence for multiple loci from a genome scan of autism kindreds.

We performed a genome-wide linkage scan using highly polymorphic microsatellite markers. To minimize genetic heterogeneity, we focused on sibpairs meeting the strict diagnosis of autism. In our primary analyses, we observed a strong linkage signal (P=0.0006, 133.16 cM) on chromosome 7q at a location coincident with other linkage studies. When a more relaxed diagnostic criteria was used, linkage evidence at this location was weaker (P=0.01). The sample was stratified into families with only male affected subjects (MO) and families with at least one female affected subject (FC). The strongest signal unique to the MO group was on chromosome 11 (P=0.0009, 83.82 cM), and for the FC group on chromosome 4 (P=0.002, 111.41 cM). We also divided the sample into regression positive and regression negative families. The regression-positive group showed modest linkage signals on chromosomes 10 (P=0.003, 0 cM) and 14 (P=0.005, 104.2 cM). More significant peaks were seen in the regression negative group on chromosomes 3 (P=0.0002, 140.06 cM) and 4 (P=0.0005, 111.41 cM). Finally, we used language acquisition data as a quantitative trait in our linkage analysis and observed a chromosome 9 signal (149.01 cM) of P=0.00006 and an empirical P-value of 0.0008 at the same location. Our work provides strong conformation for an autism locus on 7q and suggestive evidence for several other chromosomal locations. Diagnostic specificity and detailed analysis of the autism phenotype is critical for identifying autism loci.

Sequence variants of the DRD4 gene in autism: further evidence that rare DRD4 7R haplotypes are ADHD specific.

A high prevalence of rare dopamine receptor D4 (DRD4) alleles in children diagnosed with attention-deficit hyperactivity disorder (ADHD) has been reported [Grady et al., 2003]. In this prior study, extensive resequencing/haplotype data of the DRD4 locus was used to suggest that population stratification was not the explanation for the high prevalence of rare alleles. In the current study, DNA resequencing/haplotyping was conducted on 136 DRD4 alleles obtained from autism probands, collected from the same geographic population as the prior ADHD probands (Orange County, CA). A number of studies have suggested that the susceptibility genes underlying these two disorders might partially overlap. Rare DRD4 variants were not uncovered in this autism sample beyond that expected by chance. These results suggest strongly that the high prevalence of rare DRD4 alleles in ADHD probands is due to ascertainment of the sample by diagnosis of ADHD.

Bipolar disorder: dominant or recessive on chromosome 5?

The presence of a susceptibility locus for bipolar disorder on chromosome 5p near the dopamine transporter gene has been suggested. We examined 52 bipolar families for linkage to two markers in this region under both dominant and recessive models of inheritance. The purpose of the analyses was to determine the mode of inheritance of this purported bipolar locus. We also ran sensitivity analyses to confirm the reliability of the linkage results. Our results suggest that a bipolar locus inherited in an autosomal dominant fashion may be linked to this region in a subset of families.

Estimating recombination fraction separately for males and females: a counterintuitive result.

In the course of performing a linkage analysis on rats bred from inbred doubly heterozygous parents, we observed the following counterintuitive finding: the lod scores more strongly supported the hypothesis that all the recombinations occurred in one sex (without specifying which sex), rather than that some recombinations occurred in each sex. In this brief paper we explain how this apparent anomaly can arise. We point out that very different values of the recombination fraction vector theta = (theta Male, theta Female) can give rise to likelihoods that do not differ by much. We suggest that caution be exercised when investigators interpret results of linkage analyses in which estimates of theta Male and theta Female differ widely.

Preliminary implementation of new data mining techniques for the analysis of simulation data from Genetic Analysis Workshop 12: problem 2.

We introduce a new data mining method applicable to complex disease genetics. Our approach is suited to a broad spectrum of diseases, identifying the noteworthy sharing of combinations of alleles in unrelated affected individuals. Furthermore, this approach may be extended to comprise the common types of genotype data, including single-nucleotide polymorphisms, candidate-gene sequences, etc. Using a method derived from data-mining computer algorithms, we analyze a data set of unrelated affected individuals chosen from the simulated pedigrees of problem 2 of the Genetics Analysis Workshop 12. We observe that most marker subsets containing a flanking marker for each of six or seven of the disease-gene loci yield significant numbers of individuals manifesting substantially similar genotypes. However, initial attempts (blind to the generating model) to identify the predisposing loci have not been successful. Refining our methods so that such loci may routinely be found and validated is underway.

Putative non-Mendelian transmission of retinoblastoma in males: a phenotypic segregation analysis of 150 pedigrees.

In a previous genotypic study of eight families, we described paternal segregation distortion favoring the transmission of mutant alleles at the retinoblastoma gene locus (RB1). In the current study, we reviewed all published retinoblastoma pedigrees with defined ascertainment (n = 150), to determine whether the phenotypic segregation frequency at the RB1 locus is in general influenced by the sex of the transmitting parent. Segregation analysis under complete ascertainment revealed that 49.1% of the offspring of male transmitters were affected, while 44.3% of the offspring of female transmitters were affected. While this difference is not statistically significant, it is consistent with the previous findings. No significant sex distortion could be detected among the progeny of carrier fathers and mothers. In order to quantify the transmission ratio more precisely further prospective molecular genetic analysis is warranted. We propose a biological mechanism to account for a putative segregation distortion, namely that genetic recombination creates clones of spermatogonia that are homozygous for the mutant RB1 allele leading to a non-Mendelian ratio of sperm. This model can be experimentally tested using amplification of DNA from single sperm cells.