Abstract
AIMS: The extent to which maternal transmission of primary dysmenorrhoea is genetically determined in adolescents and young women has yet to be determined. We aimed to assess heritability and associations relevant to primary pain syndromes using a twin family study. METHODS: Participants were young menstruating female twins, and their oldest sisters and mothers, whose families were registered with Twins Research Australia and previously participated in a twin family study of primary paediatric pain disorders. Questionnaire packs were mailed, assessing current maximum and average menstrual pain intensity, current pain interference with activities and retrospective dysmenorrhea secondary symptoms. RESULTS: The sample comprised 206 twin individuals (57 monozygous (MZ) and 46 dizygous (DZ) pairs) aged 10-22 years, eldest siblings (n = 38) aged 13-28 years and mothers (n = 101) aged 32-61 years. The estimated regression coefficient of the relationship between mother-daughter and twin-sibling dyads indicated significant associations for the measures of dysmenorrhea and supported heritability. Adjusted for age, the within twin-pair correlation for MZ twins was generally more than twice that of DZ twins. Heritability estimates were maximal pain intensity 0.67 (P = 3.8 × 10(-11) ), average pain intensity 0.63 (P = 3.7 × 10(-10) ), pain interference 0.57 (P = 1.8 × 10(-8) ) and retrospective symptoms 0.57 (P = 1.8 × 10(-8) ). Twin individuals with a lifetime (three-month) history of iron deficiency and those with painless restless legs syndrome (RLS) were significantly more likely to have more intense pain associated with menstruation. CONCLUSION: Primary dysmenorrhea in adolescents and young women was shown to be relatively strongly genetically influenced and associated especially with a history of iron deficiency and painless RLS which have potential therapeutic implications.