Birth order and narcolepsy risk among genetically susceptible individuals: a population-based case-control study.

Abstract

BACKGROUND:

Birth order may play a role in autoimmune diseases and early childhood infections, both factors implicated in the etiology of narcolepsy. We investigated the association between birth order and narcolepsy risk in a population-based case-control study in which all study subjects were HLA-DQB1*0602 positive.

METHODS:

Subjects were 18-50 years old, residents of King County, Washington, and positive for HLA-DQB1*0602. Birth order was obtained from administered interviews. We used logistic regression to generate odds ratios adjusted for income and African American race.

RESULTS:

Analyses included 67 cases (mean age 34.3 [SD=9.1], 70.2% female) and 95 controls (mean age 35.1 [SD=8.8], 58.1% female). Associations for birth order were as follows: first born (cases 38.8% vs. controls 50.2%, OR=1.0; reference), second born (cases 29.9% vs. controls 32.9%, OR=1.6; 95% CI 0.7, 3.7), and third born or higher (cases 31.3% vs. controls 16.8%, OR=2.5; 95% CI 1.0, 6.0). A linear trend was significant (p<0.05). Sibling number, sibling gender, having children, and number of children did not differ significantly between narcolepsy cases and controls.

CONCLUSIONS:

Narcolepsy risk was significantly associated with higher birth order in this population-based study of genetically susceptible individuals. This finding supports an environmental influence on narcolepsy risk through an autoimmune mechanism, early childhood infections, or both.

• Authors: Nathaniel F Watson, Thanh G N Ton, Thomas D Koepsell, W T Longstreth Jr
• Journal: Sleep medicine (Sleep Med) Vol. 13 Issue 3 Pg. 310-3 (Mar 2012) ISSN: 1878-5506 [Electronic] Netherlands
• PMID: 22281000 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
• Copyright: Copyright © 2011 Elsevier B.V. All rights reserved.

Chemical References

• Autoantibodies
• HLA-DQ beta-Chains
• HLA-DQB1 antigen

Topics

• Adolescent
• Adult
• Autoantibodies (immunology)
• Autoimmune Diseases (epidemiology, genetics, immunology)
• Birth Order
• Case-Control Studies
• Female
• Genetic Predisposition to Disease (epidemiology, genetics)
• HLA-DQ beta-Chains (genetics, immunology)
• Humans
• Male
• Middle Aged
• Narcolepsy (epidemiology, genetics, immunology)
• Risk Factors
• Young Adult