ORIGINAL ARTICLE Heritability of Recurrent Tonsillitis Ellen Kvestad, MD; Kari Jorunn Kværner, MD, PhD; Espen Røysamb, PhD; Kristian Tambs, PhD; Jennifer Ruth Harris, PhD; Per Magnus, MD, PhD Objective: To estimate the relative contribution of ge- netic and environmental effects on the variance in the liability of recurrent tonsillitis. Design: Retrospective questionnaire data from a popu- lation-based cohort. Setting: Population-based data from Norway. Participants: A total of 9479 Norwegian twins born be- tween January 1, 1967, and December 31, 1979, identi- fied through the Medical Birth Registry of Norway. Main Outcome Measure: Recurrent tonsillitis. Results: The lifetime prevalence of recurrent tonsillitis was 11.7% (95% confidence interval, 11.0%-12.3%), with a significant predominance of female cases. The tetra- choric correlations for monozygotic twins were 0.71 for males and 0.60 for females. For dizygotic twins, the cor- relations were 0.12 for males, 0.14 for females, and 0.24 for dizygotic pairs of opposite sex. Structural equation modeling indicated that genetic effects explained 62% of the variation in the liability of recurrent tonsillitis. The remaining variance was attributed to individual environ- mental effects. There was no evidence of sex-specific ge- netic effects on the liability of recurrent tonsillitis. Conclusion: There is evidence for a substantial genetic predisposition for recurrent tonsillitis. Arch Otolaryngol Head Neck Surg. 2005;131:383-387 T ONSILLITIS IS A COMMON childhood infectious dis- ease that involves the pa- renchyma of the palatine tonsils. Although tonsilli- tis has few long-term effects, recurrent ton- sillitis causes significant morbidity and time lost from school or work. 1 The defi- nition of recurrent may vary somewhat, but the criteria used recently as a measure of severity were 5 or more episodes of true tonsillitis per year, symptoms recurring for at least a year, and episodes that are dis- abling and that prevent normal function- ing. 1 In children, sore throat may be part of the early symptom complex of upper respiratory tract morbidity. Although most other childhood upper respiratory tract dis- eases tend to improve with time, there is no evidence of spontaneous resolution of recurrent tonsillitis. 2 The limited data avail- able provide no evidence of a difference between surgical and medical treatment for recurrent tonsillitis. 1 To date, neither genetic nor environ- mental risk factors for tonsillitis have been fully explored. A previous case-control study 3 reported that parental atopy and pa- rental history of tonsillectomy predict sub- sequent tonsillitis in their children. Fa- milial clustering of tonsillectomy has been shown in a small clinical study, 4 but the study was not designed to distinguish be- tween these 2 sources of variance. An- other study 5 reported that heritability of tonsillectomy varies with time, suggest- ing a cohort effect in the heritability of this phenotype. To our knowledge, the heri- tability of recurrent tonsillitis has not pre- viously been reported. The aim of the present study is to estimate the relative contribution of genetic and environmen- tal effects in the liability of recurrent ton- sillitis in a population-based data sample of Norwegian twins. METHODS SAMPLE The Norwegian Institute of Public Health Twin Study has a dynamic cohort design. The cur- rent database includes information on twins born between January 1, 1967, and December 31, 1979, identified through the Medical Birth Registry of Norway. Two questionnaire stud- ies have been conducted so far, in 1992 and 1998, with individual response rates of 73% and 63% and pairwise response rates of 64% and 52%, respectively. The 1992 question- Author Affiliations: Division of Epidemiology, Norwegian Institute of Public Health, Oslo (Drs Kvestad, Røysamb, Tambs, Harris, and Magnus), and Department of Otorhinolaryngology, Akershus University Hospital, University of Oslo (Dr Kværner). Financial Disclosure: None. (REPRINTED) ARCH OTOLARYNGOL HEAD NECK SURG/ VOL 131, MAY 2005 WWW.ARCHOTO.COM 383 ©2005 American Medical Association. All rights reserved. Downloaded From: http://archotol.jamanetwork.com/ on 12/02/2015