SAN FRANCISCO – Simone Appenzeller, MD, PhD, reported at an international congress on systemic lupus erythematosus.
She presented a cross-sectional study of 760 consecutive SLE patients seen in a university lupus clinic and 700 healthy controls. Ninety-eight of the lupus patients had childhood-onset disease that began no later than age 16 years, while 662 had adult-onset SLE.
Southeastern Brazil, where the study was conducted, features a mostly subtropical climate with relatively mild winters. Because it is in the southern hemisphere, winter lasts from June 21 to September 21, while spring runs from September 22 to December 20.
Forty-six percent of subjects with childhood-onset SLE were born in winter, 17% in spring, another 17% in summer, and just over 19% in autumn, according to Dr. Appenzeller, a rheumatologist at the University of Campinas (Brazil).
In contrast, the occurrence of adult-onset SLE showed no variation by birth month or season.
The birth disparity between childhood- and adult-onset SLE was greatest in August, the depth of Brazilian winter, when 15.3% of all subjects with childhood-onset SLE were born, compared with 9% of adult-onset SLE patients and 8% of healthy controls.
The explanation for the increased likelihood of patients with childhood-onset SLE to be born in the winter months probably involves a gene-environment interaction, Dr. Appenzeller said. The most likely environmental factors are low seasonal maternal vitamin D levels and/or exposure to winter respiratory infections. The existence of a genetic component to the birth month disparity is suggested by another study by the Brazilian investigators in which they determined that the prevalence of SLE in both the first- and second-degree relatives of individuals with childhood-onset SLE was significantly higher than in patients with adult-onset disease.
Dr. Appenzeller reported having no financial conflicts regarding her study, funded by the Brazilian National Council for Scientific and Technological Development and other noncommercial research organizations.