Variation of serum creatine kinase levels with age in normal females: implications for genetic counselling in Duchenne muscular dystrophy.

We have examined the variation of creatine kinase (CK) levels with age in 206 unrelated normal females. The subjects included 75 adult women aged 15-50, 11 post-menopausal women aged 50-70 and 120 girls under 15 years of age, comprising 84 girls with idiopathic epilepsy (65 pre-menarchal and 19 post-menarchal), well controlled on various anticonvulsant combinations, and 36 normal schoolgirl volunteers (28 pre-menarchal and 8 post-menarchal). Comparison of mean and variance values showed no significant difference between the CK levels in normal and epileptic girls and the data were subsequently combined. Creatine kinase levels were significantly higher in the pre-menarchal girls than in the post-menarchal girls and normal adult women. Levels were high in the first few months of life, fell during infancy and early childhood, rose rapidly in later childhood and then fell abruptly around the time of menarche. The levels then fell slowly throughout adult life but rose again after age 40. This phasic variation with age may be related to hormonal status. The use of age-specific CK ranges may have a significant effect on the carrier detection rate in Duchenne dystrophy.