Environmental risk factors and clinical phenotype in familial and sporadic primary blepharospasm.

BACKGROUND: Although environmental and genetic factors may contribute to the etiology of blepharospasm, their relative contribution in causing familial and sporadic blepharospasm is unknown. METHODS: First-degree relatives of 122 patients with primary blepharospasm were examined with a validated 2-step diagnostic procedure, including a screening questionnaire and examination of some relatives. Examiners were blinded to the questionnaire data for family history of probands. Data for demographic and clinical features, prior ophthalmologic complaints, and nondecaffeinated coffee intake were collected from probands before family investigation. RESULTS: Dystonia was diagnosed in 27 relatives from 23 families (20\% rate of family history for dystonia). No significant differences were found between familial and sporadic cases in the frequency of coffee drinking and eye diseases or in sex, age at onset, or tendency to spread. Multivariable conditional logistic analysis testing of 67 case patients and 127 family-matched unaffected siblings yielded a significant positive association between blepharospasm and prior eye diseases (adjusted odds ratio [OR] 2.5; 95\% confidence interval [CI] 1.1-6.1; p = 0.03) and a significant inverse association between case status and ever coffee drinking (adjusted OR 0.23; 95\% CI 0.1-0.8; p = 0.02). CONCLUSIONS: The new information from this large family-based study on primary blepharospasm strongly supports eye diseases and coffee as risk factors for blepharospasm. The finding that the 2 environmental exposures exerted a similar influence on familial and sporadic blepharospasm, together with the convergent phenotypic expression in familial and sporadic cases, implies that familial and sporadic blepharospasm probably share a common etiologic background.