{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,4]],"date-time":"2026-10-04T22:23:42Z","timestamp":1791152622377,"version":"4.1.0"},"reference-count":36,"publisher":"SAGE Publications","issue":"9","license":[{"start":{"date-parts":[[1992,11,1]],"date-time":"1992-11-01T00:00:00Z","timestamp":720576000000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.sagepub.com\/page\/policies\/text-and-data-mining-license"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J Learn Disabil"],"published-print":{"date-parts":[[1992,11]]},"abstract":"<jats:p>\n                    Recent research has raised the question of whether age- and IQ-discrepancy forms of reading disability (RD) are distinguishable in terms of either their underlying linguistic deficit or their response to treatment, thus threatening the external validity of the traditional distinction between specific reading retardation and reading backwardness. The present study pursued the external validity of this distinction in three domains: (a) genetic etiology, (b) sex ratio and clinical correlates, and (c) neuropsychological profiles. Each of these domains was explored in the RD (n=640) and control (n=436) twins participating in the Colorado Reading Project (514 males, 562 females, with an overall mean age of 12.42 years). Little evidence for external validity was found in terms of the clinical correlates of attention deficit-hyperactivity disorder (ADHD), immune disorders, or handedness. Most importantly, there was no evidence of differential genetic etiology of the two phenotypes in this sample, in that deficits in both phenotypes were similarly heritable (h\n                    <jats:sup>2<\/jats:sup>\n                    g=.40 and .46 for age and IQ phenotypes, respectively) and the genetic correlation between them was high (r\n                    <jats:sub>G<\/jats:sub>\n                    =.88 to .96). However, the genetic and neuropsychological profile analyses did suggest that age- and IQ-discrepancy definitions of RD may relate differentially to component reading processes, such as phonological awareness and orthographic coding.\n                  <\/jats:p>","DOI":"10.1177\/002221949202500904","type":"journal-article","created":{"date-parts":[[2008,12,24]],"date-time":"2008-12-24T02:27:07Z","timestamp":1230085627000},"page":"562-573","source":"Crossref","is-referenced-by-count":84,"title":["The External Validity of Age- Versus IQ-Discrepancy Definitions of Reading Disability"],"prefix":"10.1177","volume":"25","author":[{"given":"Bruce F.","family":"Pennington","sequence":"first","affiliation":[{"name":"Bruce F. Pennington, PhD, is a professor of psychology at the University of Denver. After graduating magna cum laude in English from Harvard University, he worked as a school-teacher and started an alternative school in the Brookline, Massachusetts, public schools. He earned his PhD in clinical psychology from Duke University in 1977. He has been doing research on children's disorders for over 15 years. He currently holds both a Research Scientist Development Award and a MERIT Award from the National..."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jeffrey W.","family":"Gilger","sequence":"additional","affiliation":[{"name":"Jeffrey W. Gilger, PhD, is currently a research scientist at the University of Denver. After earning a master's in school psychology from California State University, Hayward, he then obtained a PhD from the University of California at Santa Barbara, where he specialized in child development and behavioral genetics. Subsequently, he went on to the University of Iowa Medical School for fellowship in psychiatric genetics. He was recently awarded the 1992 Distinguished Young Researcher Award in Cognitive..."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Richard K.","family":"Olson","sequence":"additional","affiliation":[{"name":"Richard K. Olson, PhD, is professor of psychology and associate director of the Colorado Learning Disabilities Research Center."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"John C.","family":"DeFries","sequence":"additional","affiliation":[{"name":"John C. DeFries, PhD, is professor of psychology and director of the Institute for Behavioral Genetics, University of Colorado, Boulder. He is also the director of the Colorado Learning Disabilities Research Center and serves as a consulting editor for the Journal of Learning Disabilities. Address: Bruce F. Pennington, University of Denver, Psychology Department, 2155 S. Race St., Denver, CO 80208."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"179","published-online":{"date-parts":[[1992,11,1]]},"reference":[{"key":"atypb1","volume-title":"Diagnostic and statistical manual of mental disorders","author":"American Psychiatric Association","year":"1987","edition":"3"},{"key":"atypb2","volume-title":"Detroit tests of learning aptitude","author":"Baker, H.J.","year":"1959"},{"key":"atypb3","first-page":"557","volume-title":"Comprehension processes in reading","author":"Conners, F.","year":"1991"},{"key":"atypb4","doi-asserted-by":"publisher","DOI":"10.1007\/BF01066239"},{"key":"atypb5","doi-asserted-by":"publisher","DOI":"10.1017\/S0001566000003810"},{"key":"atypb6","volume-title":"Advances in the neuropsychology of learning disabilities: Issues, methods, and practices","author":"DeFries, J.C.","year":"1990"},{"key":"atypb7","first-page":"53","volume-title":"The reading brain: The biological basis of dyslexia","author":"DeFries, J.C.","year":"1991"},{"key":"atypb8","doi-asserted-by":"publisher","DOI":"10.1016\/S0160-2896(81)80012-8"},{"key":"atypb9","volume-title":"Manual for the Peabody Individual Achievement Test","author":"Dunn, L.M.","year":"1970"},{"key":"atypb10","first-page":"15","volume-title":"Neuropsychological validation of learning disability subtypes","author":"Francis, D.J.","year":"1991"},{"key":"atypb11","volume-title":"Manual for a kit of reference tests for cognitive factors","author":"French, J.W.","year":"1963"},{"key":"atypb12","doi-asserted-by":"publisher","DOI":"10.1007\/BF00354964"},{"key":"atypb13","volume-title":"Paper presented at the annual meeting of the Behavior Genetics Association","author":"Gilger, J.W."},{"key":"atypb14","volume-title":"Paper presented at the 20th annual meeting of the International Neuropsychological Society","author":"Gilger, J.W."},{"key":"atypb15","doi-asserted-by":"publisher","DOI":"10.1097\/00004583-199203000-00024"},{"issue":"3","key":"atypb16","first-page":"209","volume":"30","author":"Gilger, J.W.","year":"1992","journal-title":"Neuro-psychologia"},{"key":"atypb17","first-page":"1","volume":"65","author":"Hallgren, B.","year":"1950","journal-title":"Acta Psychiatrica et Neurologica Supplement"},{"key":"atypb18","doi-asserted-by":"publisher","DOI":"10.1007\/BF00912324"},{"key":"atypb19","first-page":"61","volume":"20","author":"Nettleship, E.","year":"1901","journal-title":"Ophthalmic Review"},{"key":"atypb20","first-page":"265","volume":"16","author":"Nichols, R.C.","year":"1966","journal-title":"Acta Geneticae Medicae et Gemellologiae"},{"key":"atypb21","doi-asserted-by":"publisher","DOI":"10.1007\/BF00354960"},{"key":"atypb22","doi-asserted-by":"publisher","DOI":"10.1177\/002221948902200604"},{"key":"atypb23","doi-asserted-by":"publisher","DOI":"10.1001\/jama.1991.03470110073036"},{"key":"atypb24","doi-asserted-by":"publisher","DOI":"10.1111\/j.2044-8279.1983.tb02570.x"},{"key":"atypb25","doi-asserted-by":"publisher","DOI":"10.1111\/j.1469-7610.1975.tb01269.x"},{"key":"atypb26","volume-title":"The primary mental abilities: Technical report","author":"Science Research Associates","year":"1965"},{"key":"atypb27","doi-asserted-by":"publisher","DOI":"10.1111\/j.2044-835X.1987.tb01039.x"},{"key":"atypb28","doi-asserted-by":"publisher","DOI":"10.1056\/NEJM199201163260301"},{"key":"atypb29","doi-asserted-by":"publisher","DOI":"10.1111\/j.1469-7610.1985.tb01942.x"},{"key":"atypb30","doi-asserted-by":"publisher","DOI":"10.1007\/BF00354963"},{"key":"atypb31","doi-asserted-by":"publisher","DOI":"10.1598\/RRQ.21.4.1"},{"key":"atypb32","doi-asserted-by":"publisher","DOI":"10.1007\/BF02659181"},{"key":"atypb33","doi-asserted-by":"publisher","DOI":"10.1002\/acp.2350020107"},{"key":"atypb34","volume-title":"Identifying sex differences in reading disability: Lessons from a twin study","author":"Stevenson, J.","year":"1991"},{"key":"atypb35","volume-title":"Examiner's manual: Wechsler Intelligence Scale for Children-Revised","author":"Wechsler, D.","year":"1974"},{"key":"atypb36","volume-title":"Examiner's manual: Wechsler Intelligence Adult Scale-Revised","author":"Wechsler, D.","year":"1981"}],"container-title":["Journal of Learning Disabilities"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/journals.sagepub.com\/doi\/pdf\/10.1177\/002221949202500904","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/journals.sagepub.com\/doi\/pdf\/10.1177\/002221949202500904","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,5,1]],"date-time":"2026-05-01T07:10:11Z","timestamp":1777619411000},"score":1,"resource":{"primary":{"URL":"https:\/\/journals.sagepub.com\/doi\/10.1177\/002221949202500904"}},"subtitle":["Lessons From a Twin Study"],"short-title":[],"issued":{"date-parts":[[1992,11]]},"references-count":36,"journal-issue":{"issue":"9","published-print":{"date-parts":[[1992,11]]}},"alternative-id":["10.1177\/002221949202500904"],"URL":"https:\/\/doi.org\/10.1177\/002221949202500904","relation":{},"ISSN":["0022-2194","1538-4780"],"issn-type":[{"value":"0022-2194","type":"print"},{"value":"1538-4780","type":"electronic"}],"subject":[],"published":{"date-parts":[[1992,11]]}}}