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Biomedical subjects

S E Hodge

Publications and source records attributed to S E Hodge.

At least 19 recordsLinked to original sources
PubMed2001

Excess of twins among affected sibling pairs with autism: implications for the etiology of autism.

It is widely accepted that genes play a role in the etiology of autism. Evidence for this derives, in part, from twin data. However, despite converging evidence from gene-mapping studies, aspects of the genetic contribution remain obscure. In a sample of families selected because each had exactly two affected sibs, we observed a remarkably high proportion of affected twin pairs, both MZ and DZ. Of 166 affected sib pairs, 30 (12 MZ, 17 DZ, and 1 of unknown zygosity) were twin pairs. Deviation from expected values was statistically significant (P<10(-6) for all twins); in a similarly ascertained sample of individuals with type I diabetes, there was no deviation from expected values. We demonstrate that to ascribe the excess of twins with autism solely to ascertainment bias would require very large ascertainment factors; for example, affected twin pairs would need to be, on average, approximately 10 times more likely to be ascertained than affected non-twin sib pairs (or 7 times more likely if "stoppage" plays a role). Either risk factors (related to twinning or to fetal development) or other factors (genetic or nongenetic) in the parents may contribute to autism.

Autistic Disorder↗
PubMed2001

Model-free vs. model-based linkage analysis: a false dichotomy?

The aim of this article is to dispel some misunderstandings concerning the concepts of model-free or nonparametric linkage analysis (usually meaning affecteds-only analysis) and model-based or parametric analysis (usually meaning classical lod scores) and the implications of these concepts for the linkage analysis of complex genetic diseases. I review basic principles and then briefly indicate actual research findings. Readers may be surprised to learn that, technically, lod score analysis is also nonparametric. All this taken together indicates that classical lod score analysis, performed under a couple of different sets of genetic assumptions and corrected for multiple tests, is often actually superior to model-free analyses, even when the true genetic model is complex and unknown.

Computer Simulation↗
PubMed2001

Stoppage: an issue for segregation analysis.

Segregation analysis assumes that the observed family-size distribution (FSD), i.e., distribution of number of offspring among nuclear families, is independent of the segregation ratio p. However, for certain serious diseases with early onset and diagnosis (e.g., autism), parents may change their original desired family size, based on having one or more affected children, thus violating that assumption. Here we investigate "stoppage," the situation in which such parents have fewer children than originally planned. Following Brookfield et al. [J Med Genet 25:181-185, 1988], we define a stoppage probability d that after the birth of an affected child, parents will stop having children and thus not reach their original desired family size. We first derive the full correct likelihood for a simple segregation analysis as a function of p, d, and the ascertainment probability pi. We show that p can be estimated from this likelihood if the FSD is known. Then, we show that under "random" ascertainment, the presence of stoppage does not bias estimates of p. However, for other ascertainment schemes, we show that is not the case. We use a simulation study to assess the magnitude of bias, and we demonstrate that ignoring the effect of stoppage can seriously bias the estimates of p when the FSD is ignored. In conclusion, stoppage, a realistic scenario for some complex diseases, can represent a serious and potentially intractable problem for segregation analysis.

Family Characteristics↗
PubMed2001

No association or linkage between polymorphisms in the genes encoding cholecystokinin and the cholecystokinin B receptor and panic disorder.

Growing animal data implicate cholecystokinin in the regulation of anxiety, while human clinical research confirms the role of cholecystokinin in the provocation of panic attacks. Antipanic medications suppress the ability of cholecystokinin to induce panic attacks, and may alter the expression of the cholecystokinin gene. Thus, there is increased interest in understanding the molecular genetic component of these observations. Recent association studies using persons with panic disorder described some association between polymorphisms in the genes encoding cholecystokinin and the cholecystokinin B-receptor and panic disorder. In this study, we used a family-based design, employing 596 individuals in 70 panic disorder pedigrees, as well as 77 haplotype relative risk 'triads'. Subjects were genotyped for two polymorphisms: the polymorphic microsatellite marker in the CCK-BR locus using PCR-based genotyping and at a single nucleotide polymorphism in the CCK promoter using a fluorescence polarization detection assay, and the data were analyzed for genetic association and linkage. Employing a variety of diagnostic and genetic models, linkage analysis produced no significant lod scores at either locus. Family-based tests of association, the haplotype-based haplotype relative risk statistic and the transmission disequilibrium test, were likewise non-significant. The results reported here provide little support for the role of these polymorphisms in panic disorder.

Cholecystokinin↗
PubMed2000

Drawbacks of GENEHUNTER for larger pedigrees: application to panic disorder.

Large pedigrees can pose a problem for GENEHUNTER linkage analysis software. Differences in two-point and multipoint lodscores were observed when comparing GENEHUNTER to other linkage software. Careful consideration must be given when selecting linkage analysis programs. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:781-783, 2000.

Chromosome Mapping↗
PubMed2000

Familial primary pulmonary hypertension (gene PPH1) is caused by mutations in the bone morphogenetic protein receptor-II gene.

Familial primary pulmonary hypertension is a rare autosomal dominant disorder that has reduced penetrance and that has been mapped to a 3-cM region on chromosome 2q33 (locus PPH1). The phenotype is characterized by monoclonal plexiform lesions of proliferating endothelial cells in pulmonary arterioles. These lesions lead to elevated pulmonary-artery pressures, right-ventricular failure, and death. Although primary pulmonary hypertension is rare, cases secondary to known etiologies are more common and include those associated with the appetite-suppressant drugs, including phentermine-fenfluramine. We genotyped 35 multiplex families with the disorder, using 27 microsatellite markers; we constructed disease haplotypes; and we looked for evidence of haplotype sharing across families, using the program TRANSMIT. Suggestive evidence of sharing was observed with markers GGAA19e07 and D2S307, and three nearby candidate genes were examined by denaturing high-performance liquid chromatography on individuals from 19 families. One of these genes (BMPR2), which encodes bone morphogenetic protein receptor type II, was found to contain five mutations that predict premature termination of the protein product and two missense mutations. These mutations were not observed in 196 control chromosomes. These findings indicate that the bone morphogenetic protein-signaling pathway is defective in patients with primary pulmonary hypertension and may implicate the pathway in the nonfamilial forms of the disease.

Amino Acid Sequence↗
PubMed2000

Investigation of dopamine receptor (DRD4) and dopamine transporter (DAT) polymorphisms for genetic linkage or association to panic disorder.

Clinical and animal studies suggest a role for the neurotransmitter dopamine in anxiety states. In humans, one such condition is panic disorder, which is typified by recurrent panic attacks accompanied by anticipatory anxiety. Family, segregation, and twin studies imply a genetic component to the pathophysiology of panic disorder. In this study, we examined the genes for the D4 dopamine receptor (DRD4) and the dopamine transporter (DAT) using three common sequence polymorphisms. Two of these polymorphisms were in DRD4, a 12 base-pair insertion/deletion in exon 1 and a 48 base-pair repeat in exon 3, and the third was a 40 base-pair repeat in the 3' untranslated region of DAT. We employed a family-based design, using 622 individuals in 70 families, as well as 82 haplotype relative risk "trios". Subjects were genotyped at the polymorphic loci, and the data were analyzed for genetic association and linkage. There were no significant differences in allele frequencies or occurrence of genotypes within the triads for any of the three polymorphisms. No significant linkage between the DRD4 or DAT polymorphisms and panic disorder was observed in the multiplex families, using a variety of simulations for dominant and recessive models of inheritance. However, LOD scores of approximately 1.1 and 1.05 were observed for the DAT and DRD4 exon 1 loci, respectively. The results reported here provide little support for the role of these polymorphisms in panic disorder.

Alleles↗
PubMed2000

Potential panic disorder syndrome: clinical and genetic linkage evidence.

This paper reports evidence for a possible "chromosome 13 syndrome," which includes panic disorder, kidney or bladder problems, serious headaches, thyroid problems (usually hypothyroid), and/or mitral valve prolapse (MVP). In the course of a genetic linkage study of panic disorder, we noted these medical conditions in individual family members. (We were blind to family relationships and marker data.) We hypothesized that there may exist a subgroup of panic families with these medical conditions, which for simplicity we called it the "syndrome." Subsequently we reclassified the families as with or without the "syndrome" and extended the phenotype for analysis to include the above medical conditions. All these classifications were also done before the analysis and blind to marker data. We then examined our linkage results, looking for significant differences between families with and without the "syndrome" (using several definitions of the "syndrome")-i.e., testing for genetic heterogeneity. When the families with and without bladder/kidney problems were separated from each other, one marker-D13S779 (ATA26D07)-yielded a lod score of over 3 in the families with bladder/kidney problems. This lod score went up to 4.2 in these families when we diagnosed any individual with any one of the "syndrome" conditions as affected. These results were statistically significant even after applying an extremely overconservative Bonferroni correction for multiple tests. We present these results in order to alert other investigators working on panic disorder, for replication. If replicated, one may hypothesize that a candidate gene for the syndrome should be expressed in CNS, kidney, gut, thyroid, etc. We also noted that two independent studies report recent linkage findings between schizophrenia and the same region on chromosome 13. No connection between schizophrenia and panic disorder has ever been reported. Finally, we suggest that genetic studies of psychiatric disorders might prove more fruitful if phenotypes were expanded to include possible manifestations of the disorder in medical (non-mental) symptoms. Am. J. Med. Genet.(Neuropsychiatr. Genet.) 96:24-35, 2000.

Genetic Linkage↗
PubMed2000

Fine mapping of PPH1, a gene for familial primary pulmonary hypertension, to a 3-cM region on chromosome 2q33.

Familial primary pulmonary hypertension (PPH) is a rare autosomal dominant disease characterized by distinctive changes in pulmonary arterioles that lead to increased pulmonary artery pressures, right ventricular failure, and death. Our previous studies had mapped the disease locus, PPH1, to a 27-cM region on chromosome 2q31-q33, with a maximum multipoint logarithm of the odds favoring genetic linkage score of 3.87 with markers D2S350 and D2S364. To narrow the minimal genetic region for PPH, we physically mapped 33 highly polymorphic microsatellite markers and used them to genotype 44 affected individuals and 133 unaffected individuals from 17 families with PPH. We observed recombination events that substantially reduced the interval for PPH1 to the approximately 3-cM region that separates D2S311 and D2S1384. This entire region lies within chromosome 2q33. A maximum two-point lod score of 7.23 at a recombination fraction of zero was obtained for marker D2S307. A maximum multipoint lod score of 7.41 was observed close to marker D2S1367. The current minimal genetic region contains multiple candidate genes for PPH, including a locus thought to play a role in lung cancer.

Chromosome Aberrations↗
PubMed1999

Parent-of-origin effect in panic disorder.

Parent-of-origin effect was examined in a series of 64 pedigrees with panic disorder (PD) under both the narrow and broad diagnostic models. The narrow diagnostic model defined the affected phenotype to include only the "definite" and "probable" forms of PD, whereas the broad diagnostic model included the entire PD symptomatology. The pattern of maternal vs. paternal transmission of disease was analyzed through a number of comparisons. These comparisons were performed first on all pedigrees and then on a subset of "pure" pedigrees including only strictly maternal transmission or strictly paternal transmission of PD. There were no significant differences in the proportion of offspring born to transmitting mothers vs. transmitting fathers under either diagnostic model or pedigree set. When the difference in the sex ratio among affected offspring from both transmission types was considered, only the "pure" pedigree sample under the broad diagnostic model yielded nominally (i.e., not corrected for multiple tests) significant results (P < .05). Also, the comparisons of cumulative lifetime risk for PD between offspring of transmitting mothers and fathers gave some nominally significant results; when affected and unaffected offspring were considered, significant results were observed under the narrow and broad diagnostic models, P < .0005 and P < .05, respectively. These findings must be considered provisional until confirmed by further study.

Adolescent↗
PubMed1999

Calculating posterior cystic fibrosis risk with echogenic bowel and one characterized cystic fibrosis mutation: avoiding pitfalls in the risk calculations.

We describe a general approach to derive fetal risk following two separate test results that each raise the likelihood of the same fetal abnormality without clearly determining whether the abnormality exists. Echogenic bowel observed on fetal ultrasonography may have multiple causes, including an a priori risk of approximately 1% of cystic fibrosis (CF). On numerous occasions our laboratory tests have detected only normal cystic fibrosis transmembrane regulator (CFTR) alleles in fetuses with echogenic bowel. This result indicates that another cause most likely explains the abnormal ultrasound finding. One of our tested fetuses was heterozygous for the deltaF508 CFTR mutation and had a normal karyotype. Over 770 CFTR mutations have been described, and a significant proportion of parental mutant alleles could not be detected by our 25-mutation test. Further mutation analysis demonstrated that the fetus' mother carried the deltaF508 mutation but the father (of different ethnic background than the mother) did not carry a detectable mutation. Thus, this test result substantially increased the risk of the fetus having CF, while still not giving a definitive answer to whether the fetus was affected. A rigorous mathematical analysis determined that the 1% risk of CF following ultrasound study was increased to slightly under 12% following DNA analysis. The case is described, and the mathematical formulas are explained and illustrated with examples, along with a review of conditional probability (Appendix 2).

Bayes Theorem↗
PubMed1999

Simulated data for a complex genetic trait (problem 2 for GAW11): how the model was developed, and why.

This paper describes a simulated data set created as Problem 2 for GAW11. The generating model for Problem 2 involved two different genetic diseases, or "types," in three separate populations. The two-locus (2L) type results from the epistatic interaction of two genetic loci, and the three-allele type, from a single locus with two disease-causing alleles and one normal allele. Each type has two phenotypic forms: Mild and Severe. Both forms are subject to both genetic and environmental influences. The disease occurs in three different hypothetical populations, each with different disease allele frequencies and penetrances. In two populations there is also a fourth locus with an allele that is associated with the 2L type. Misdiagnosis can occur, but only after a family has already been ascertained through > or = 2 "genetically" affected offspring. Finally, the three different populations are studied by four different hypothetical research groups. These groups each have their own ideas about how the disease is inherited and have therefore devised different ascertainment schemes based on those beliefs. Each research group collected 100-family data sets, including data on 300 markers on six chromosomes and measurements on disease status and on the proposed two environmental factors. GAW participants were supplied with 25 random replicates of each data set.

Alleles↗
PubMed1999

Direct power comparisons between simple LOD scores and NPL scores for linkage analysis in complex diseases.

Several methods have been proposed for linkage analysis of complex traits with unknown mode of inheritance. These methods include the LOD score maximized over disease models (MMLS) and the "nonparametric" linkage (NPL) statistic. In previous work, we evaluated the increase of type I error when maximizing over two or more genetic models, and we compared the power of MMLS to detect linkage, in a number of complex modes of inheritance, with analysis assuming the true model. In the present study, we compare MMLS and NPL directly. We simulated 100 data sets with 20 families each, using 26 generating models: (1) 4 intermediate models (penetrance of heterozygote between that of the two homozygotes); (2) 6 two-locus additive models; and (3) 16 two-locus heterogeneity models (admixture alpha = 1.0,.7,.5, and.3; alpha = 1.0 replicates simple Mendelian models). For LOD scores, we assumed dominant and recessive inheritance with 50% penetrance. We took the higher of the two maximum LOD scores and subtracted 0.3 to correct for multiple tests (MMLS-C). We compared expected maximum LOD scores and power, using MMLS-C and NPL as well as the true model. Since NPL uses only the affected family members, we also performed an affecteds-only analysis using MMLS-C. The MMLS-C was both uniformly more powerful than NPL for most cases we examined, except when linkage information was low, and close to the results for the true model under locus heterogeneity. We still found better power for the MMLS-C compared with NPL in affecteds-only analysis. The results show that use of two simple modes of inheritance at a fixed penetrance can have more power than NPL when the trait mode of inheritance is complex and when there is heterogeneity in the data set.

Gene Frequency↗
PubMed1999

Lack of genetic linkage or association between a functional serotonin transporter polymorphism and panic disorder.

Given the efficacy of medications that interact with the serotonin transporter (5-HTT) in the treatment of panic disorder, we have used a family-based design to test for genetic association and linkage between panic disorder and a functional polymorphism in the promoter of the gene for 5-HTT. In this study, 340 individuals in 45 families, as well as 74 haplotype relative risk 'trios' were genotyped at the polymorphic locus, which consists of a 44 base pair deletion/insertion. There were no significant differences in allele frequencies or occurrence of genotypes within the triads. No linkage between the 5-HTT polymorphism and panic disorder was observed in the multiplex families, using a variety of simulations for dominant and recessive models of inheritance. Recent reports suggest an association between the 5-HTT polymorphism and anxiety-related traits, as measured with personality assessment. The results reported here provide evidence that the genetic basis of panic disorder may be distinct from anxiety-related traits assessed by personality inventories in normal populations.

Alleles↗