A quantitative estimate of individual genetic vulnerability for a multifactorial condition: Application to bipolar illness

J. Nurnberger, T. Foroud, E. T. Meyer, K. L. Hu, L. Flury, J. Su

Abstract

We have developed an algorithm that may be applied to genomic survey data to derive estimates of genetic vulnerability for each person in a pedigree. The method utilizes data from GENEHUNTER to identify loci of interest. A 'sharing score' is computed for each allele in the pedigree at a given locus. An individual's 'locus vulnerability score' is the sum of scores for each of his or her alleles multiplied by the NPL score at the locus. The total 'vulnerability score' is then corrected for the genotypic information available for the individual at the loci of interest. This method has been applied to the NIMH Genetics Initiative Bipolar initial dataset (N = 539 persons). We have used the output from a GENEHUNTER analysis using a diagnostic model in which SA/BP, BPI, BPII, and UPR are affected, while all others are unaffected. The 33 loci with Z scores > 1.0 were included in the analysis. A bimodal distribution of vulnerability scores is produced, with affected individuals generating higher scores than unaffected (this is to be expected from the algorithm). We have also observed an effect of diagnostic subtype, such that BPI=SA/BP > BPII=UPR (Kruskal-Wallis chi square = 15.8, p= .0012). We predicted that early onset probands would have higher vulnerability scores than late onset (p=.03, controlling for the interaction of diagnosis and age of onset). These results are consistent with the assumption of multifactorial inheritance and with the hypothesis that some of the 33 loci tested are true genetic signals. They also indicate that the algorithm, while necessarily employing a crude approximation to the underlying genetics of bipolar illness, is nevertheless capable of producing clinically meaningful results in this dataset. These methods might be used to attempt prediction of illness in at-risk individuals as a part of research on risk and protective factors. In the present data, scaled vulnerability scores for unaffected persons range from 27 to 68; scores for affected individuals range from 31 to 95. Persons with a score of >55 are more likely to be affected than unaffected; those with a score of < 55 are more likely to be unaffected than affected. Using this cut-off point both sensitivity and specificity are 77%. However, it would not be appropriate for 'vulnerability scores' to be used in any form of clinical genetic counseling at this point in time. The method described is sufficiently general that it may be useful in analyzing genomic survey data from other conditions with complex inheritance. It is easily modifiable to incorporate interactions between loci as they become known or suspected. A computerized version will be available.

Original languageEnglish (US)
Number of pages1
JournalAmerican Journal of Medical Genetics - Neuropsychiatric Genetics
Volume96
Issue number4
StatePublished - Aug 7 2000

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ASJC Scopus subject areas

  • Genetics(clinical)
  • Psychiatry and Mental health
  • Cellular and Molecular Neuroscience

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