{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,7]],"date-time":"2026-03-07T22:06:58Z","timestamp":1772921218236,"version":"3.50.1"},"reference-count":31,"publisher":"American Academy of Pediatrics (AAP)","issue":"3","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2016,3,1]]},"abstract":"<jats:sec>\n                  <jats:title>BACKGROUND:<\/jats:title>\n                  <jats:p>Legg-Calv\u00e9-Perthes disease (LCPD) is an idiopathic avascular necrosis of the femoral head. Its etiology is poorly understood, although previous studies have implicated low birth weight and possible genetic determinants. The aim of this study was to identify potential birth weight and genetic associations with LCPD.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>METHODS:<\/jats:title>\n                  <jats:p>We extracted all twin pairs from the Danish Twin Registry (DTR) in which at least 1 individual had LCPD. The DTR captures every twin pair born alive in Denmark, and those with LCPD were identified by using health record linkage. Probanwise concordance was calculated to describe the likelihood that any given individual had LCPD if their co-twin was also diagnosed.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>RESULTS:<\/jats:title>\n                  <jats:p>There were 81 twin pairs: 10 monozygotic, 51 dizygotic, and 20 unclassified (unknown zygosity [UZ]). There was no association between birth weight and being the affected co-twin. Four pairs (2 dizygotic and 2 UZ) were concordant for LCPD, which is greater than would be expected assuming no familial aggregation. There were no concordant monozygotic twin pairs. The overall probandwise concordance was 0.09 (95% confidence interval [CI]: 0.01\u20130.18): 0.00 for the monozygotic, 0.08 (95% CI: 0.00\u20130.18) for the dizygotic, and 0.18 (95% CI: 0.00\u20130.40) for the UZ twin pairs.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>CONCLUSIONS:<\/jats:title>\n                  <jats:p>This study found evidence of familial clustering in LCPD but did not show a genetic component. The absolute risk that a co-twin of an affected individual will develop LCPD is low, even in the case of monozygotic twin pairs.<\/jats:p>\n               <\/jats:sec>","DOI":"10.1542\/peds.2015-3542","type":"journal-article","created":{"date-parts":[[2016,2,13]],"date-time":"2016-02-13T11:19:13Z","timestamp":1455362353000},"source":"Crossref","is-referenced-by-count":20,"title":["A Twin Study of Perthes Disease"],"prefix":"10.1542","volume":"137","author":[{"given":"David","family":"Metcalfe","sequence":"first","affiliation":[{"name":"Center for Surgery and Public Health, Harvard Medical School, Boston, Massachusetts;"},{"name":"Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, United Kingdom;"},{"name":"Warwick Medical School, University of Warwick, Coventry, United Kingdom;"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Stephanie","family":"Van Dijck","sequence":"additional","affiliation":[{"name":"Department of Orthopaedic Surgery, Middlemore Hospital, Auckland, New Zealand;"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Nicolas","family":"Parsons","sequence":"additional","affiliation":[{"name":"Warwick Medical School, University of Warwick, Coventry, United Kingdom;"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kaare","family":"Christensen","sequence":"additional","affiliation":[{"name":"The Danish Twin Registry, University of Southern Denmark, Odense, Denmark; and"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Daniel C.","family":"Perry","sequence":"additional","affiliation":[{"name":"Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"417","published-online":{"date-parts":[[2016,3,1]]},"reference":[{"issue":"5","key":"2021120919095095100_B1","doi-asserted-by":"crossref","first-page":"1673","DOI":"10.1002\/art.34316","article-title":"Legg-Calv\u00e9-Perthes disease in the UK: geographic and temporal trends in incidence reflecting differences in degree of deprivation in childhood.","volume":"64","author":"Perry","year":"2012","journal-title":"Arthritis Rheum"},{"issue":"2","key":"2021120919095095100_B2","doi-asserted-by":"crossref","first-page":"131","DOI":"10.1111\/j.1365-3016.1989.tb00505.x","article-title":"Low blood manganese levels in Liverpool children with Perthes\u2019 disease.","volume":"3","author":"Hall","year":"1989","journal-title":"Paediatr Perinat Epidemiol"},{"issue":"2","key":"2021120919095095100_B3","doi-asserted-by":"crossref","first-page":"167","DOI":"10.1302\/0301-620X.82B2 .10033","article-title":"Deprivation, urbanisation and Perthes\u2019 disease in Northern Ireland.","volume":"82","author":"Kealey","year":"2000","journal-title":"J Bone Joint Surg Br"},{"issue":"4","key":"2021120919095095100_B4","doi-asserted-by":"crossref","first-page":"351","DOI":"10.1136\/adc.84.4.351","article-title":"The incidence and distribution of Legg-Calv\u00e9-Perthes\u2019 disease in Liverpool, 1982-95.","volume":"84","author":"Margetts","year":"2001","journal-title":"Arch Dis Child"},{"issue":"1","key":"2021120919095095100_B5","doi-asserted-by":"crossref","first-page":"6","DOI":"10.1302\/0301-620X.60B1.564352","article-title":"The aetiology of Perthes\u2019 disease: genetic, epidemiological and growth factors in 310 Edinburgh and Glasgow patients.","volume":"60","author":"Wynne-Davies","year":"1978","journal-title":"J Bone Joint Surg Br"},{"issue":"6407","key":"2021120919095095100_B6","doi-asserted-by":"crossref","first-page":"1757","DOI":"10.1136\/bmj.287.6407.1757","article-title":"Perthes\u2019 disease of the hip in Liverpool.","volume":"287","author":"Hall","year":"1983","journal-title":"Br Med J (Clin Res Ed)"},{"issue":"3","key":"2021120919095095100_B7","doi-asserted-by":"crossref","first-page":"326","DOI":"10.1097\/01241398-200005000-00011","article-title":"Legg-Calv\u00e9-Perthes disease and passive smoking.","volume":"20","author":"Garc\u00eda Mata","year":"2000","journal-title":"J Pediatr Orthop"},{"issue":"6","key":"2021120919095095100_B8","doi-asserted-by":"crossref","first-page":"367","DOI":"10.1097\/01202412-200411000-00003","article-title":"Smoking and socio-economic status in the etiology and severity of Legg-Calv\u00e9-Perthes\u2019 disease.","volume":"13","author":"Gordon","year":"2004","journal-title":"J Pediatr Orthop B"},{"issue":"6","key":"2021120919095095100_B9","doi-asserted-by":"crossref","first-page":"644","DOI":"10.1097\/BPO.0b013e31829494c0","article-title":"Hyperactivity and the psychological burden of Perthes disease: a case-control study.","volume":"33","author":"Perry","year":"2013","journal-title":"J Pediatr Orthop"},{"issue":"3","key":"2021120919095095100_B10","doi-asserted-by":"crossref","first-page":"159","DOI":"10.1093\/aje\/kwr293","article-title":"Racial and geographic factors in the incidence of Legg-Calv\u00e9-Perthes\u2019 disease: a systematic review.","volume":"175","author":"Perry","year":"2012","journal-title":"Am J Epidemiol"},{"issue":"11","key":"2021120919095095100_B11","doi-asserted-by":"crossref","first-page":"2317","DOI":"10.1046\/j.1538-7836.2003.00416.x","article-title":"The beta fibrinogen gene G-455-A polymorphism is a risk factor for Legg-Perthes disease.","volume":"1","author":"Dilley","year":"2003","journal-title":"J Thromb Haemost"},{"issue":"12","key":"2021120919095095100_B12","doi-asserted-by":"crossref","first-page":"2642","DOI":"10.2106\/00004623-200412000-00009","article-title":"Legg-Calve-Perthes disease and thrombophilia.","volume":"86-A","author":"Balasa","year":"2004","journal-title":"J Bone Joint Surg Am"},{"key":"2021120919095095100_B13","doi-asserted-by":"crossref","first-page":"14","DOI":"10.1097\/01.blo.0000238799.05338.5a","article-title":"On a particular form of pseudo-coxalgia associated with a characteristic deformity of the upper end of the femur: 1910.","volume":"451","author":"Calv\u00e9","year":"2006","journal-title":"Clin Orthop Relat Res"},{"issue":"9","key":"2021120919095095100_B14","doi-asserted-by":"crossref","first-page":"2349","DOI":"10.1007\/s11999-012-2433-1","article-title":"The classic: on juvenile arthritis deformans. 1910.","volume":"470","author":"Perthes","year":"2012","journal-title":"Clin Orthop Relat Res"},{"issue":"7","key":"2021120919095095100_B15","first-page":"887","article-title":"Legg-Perthes disease in siblings; 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