Behavior Genetics

, Volume 35, Issue 4, pp 479–490 | Cite as

DeFries–Fulker Analysis of Twin Data with Skewed Distributions: Cautions and Recommendations from a Study of Children’s Use of Verb Inflections

Article

Abstract

DeFries-Fulker (DF) analysis is an adaptation of multiple regression that is used to estimate heritability of extreme scores (h2‰‰g) on a dimension. Probands are identified as scoring below a cutoff that defines impairment, and one then uses regression to predict the scores of co-twins from the proband scores and a term that denotes the genetic relationship between twins (1.0 for MZ and 0.5 for DZ twins). This paper reports illustrative data and simulations for the situation where the dimensional variable shows substantial negative skew. Two types of simulation were conducted: in the first, an underlying polygenic liability dimension was normally distributed: skewing was introduced by transforming or truncating the liability distribution. In the second set of simulations, skewing arose because an infrequent defective gene impaired scores. In both sets of simulations DF analysis was robust in the face of severe skewing of the data. DF analysis can provide two pointers to major gene effects on extreme scores on a trait with a skewed distribution: first, group heritability estimates will be higher for the original skewed data than for normalised data; second, estimates of h2‰‰g will increase as the cutoff to identify probands is made more stringent. Both these features were seen in data from a test of verb inflections given to174 6-year-old twin pairs, suggesting that a single major gene may be implicated in causing impaired grammatical development.

Key words

Genetics grammar methods specific language impairment twins 

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References

  1. Bishop, D. V. M. 2003

    Genes and language

    Krude, T. eds. DNA: Changing Science and SocietyCambridge University PressCambridge144165
    Google Scholar
  2. Bishop, D. V. M., Laws, G., Adams, C., and Norbury, C. F. (under review). High heritability of speech and language impairments in 6-year-old twins demonstrated using parent and teacher report.Google Scholar
  3. Bishop, D. V. M., North, T., Donlan, C. 1996Nonword repetition as a behavioral marker for inherited language impairment: evidence from a twin studyJ. Child Psychol. Psyc.37391403Google Scholar
  4. Dale, P. S., Price, T. S., Bishop, D. V. M., Plomin, R. 2003Outcomes of early language delay: I. Predicting persistent and transient delay at 3 and 4 yearsJ. Speech Lang. Hear. Res.46544560PubMedGoogle Scholar
  5. DeFries, J. C., Alarcon, M., Olson, R. K. 1997

    Genetic aetiologies of reading and spelling deficits: developmental differences

    Hulme, C.Snowling, M. eds. Dyslexia: Biology, Cogniion and InterventionWhurrLondon2037
    Google Scholar
  6. DeFries, J. C., Fulker, D. W. 1985Multiple regression analysis of twin dataBehav. Genet.15467473PubMedGoogle Scholar
  7. DeFries, J. C., Fulker, D. W. 1988Multiple regression analysis of twin data: aetiology of deviant scores versus individual differencesActa Genet. Med. Gemel.37205216Google Scholar
  8. Falconer, D. S., Mackay, T. F. C. 1996Introduction to Quantitative Genetics, 4th ednLongmanHarlowGoogle Scholar
  9. Lai, C. S. L., Fisher, S. E., Hurst, J. A., Vargha-Khadem, F., Monaco, A. 2001A forkhead-domain gene is mutated in a severe speech and language disorderNature413519523CrossRefPubMedGoogle Scholar
  10. Lynch, M., Walsh, B. 1998Genetics and Analysis of Quantitative TraitsSinauer AssociatesSunderland, MAGoogle Scholar
  11. Newbury, D. F. Bonora, E. Lamb, J. A. Fisher, S. E. Lai, C. S. L. Baird, G. Jannoun, L. Slonims, V. Stott, C. M. Merricks, M. J. Bolton, P. F. Bailey, A. J. Monaco, A. P. International Molecular Genetic Study of Autism Consortium.2002FOXP2 is not a major susceptibility gene for autism or specific language impairmentAm. J. Hum. Genet.7013181327PubMedGoogle Scholar
  12. Plomin, R., Dale, P. S. 2000

    Genetics and early language development: A UK study of twins

    Bishop, D. V. M.Leonard, L. B. eds. Speech and Language Impairments in Children: Causes, Characteristics, Intervention and OutcomePsychology PressHove, UK3551
    Google Scholar
  13. Purcell, S., Eley, T. C., Dale, P. S., Oliver, B., Petrill, S. A., Price, T. S., Saudino, K. J., Simonoff, E., Stevenson, J., Taylor, E., Plomin, R. 2001Comorbidity between verbal and non-verbal cognitive delays in 2-yr-olds: A bivariate twin analysisDev. Sci.4195208Google Scholar
  14. Purcell, S., Sham, P. C. 2003A model-fitting implementation of the DeFries–Fulker model for selected twin dataBehav. Genet.33271278PubMedGoogle Scholar
  15. Rice, M. L. 2000

    Grammatical symptoms of specific language impairment

    Bishop, D. V. M.Leonard, L. B. eds. Speech and Language Impairments in Children: Causes, Characteristics, Intervention and OutcomePsychology PressHove, UK1734
    Google Scholar
  16. Rice, M. L., Wexler, K. 1996Toward tense as a clinical marker of specific language impairment in English-speaking childrenJ. Speech Lang. Hear. Res.3912391257Google Scholar
  17. Rice, M. L., Wexler, K. 2001Rice/Wexler Test of Early Grammatical ImpairmentPsychological CorporationSan AntonioGoogle Scholar
  18. Stevenson, J. 1991Which aspects of processing text mediate genetic effects?Read. Writ.3249269Google Scholar
  19. Trouton, A., Spinath, F. M., Plomin, R. 2002Twins Early Development Study (TEDS): A multivariate, longitudinal genetic investigation of language, cognition and behaviour problems in childhoodTwin Res.5444448PubMedGoogle Scholar
  20. Van den Oord, E., Simonoff, E., Eaves, L., Pickles, A., Silberg, J., Maes, H. 2000An evaluation of different approaches for behavior genetic analyses with psychiatric symptom scoresBehav. Genet.30118PubMedGoogle Scholar

Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  1. 1.Department of Experimental PsychologyUniversity of OxfordOxfordUK

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