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The real onset of amyotrophic lateral sclerosis
  1. Andrew Eisen
  1. Correspondence to Professor A Eisen, University of British Columbia, 2862 Highbury Street, Vancouver, BC, Canada, USA; eisen{at}

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A biomarker that has generated considerable interest is digit ratio, the ratio of the second (index) finger to the fourth (ring) finger, 2D:4D. Men have a longer fourth digit relative to the second digit than do women, and the ratio is lower in boys and men than in girls and women.1 A reduced 2D:4D ratio is assumed to indicate reduced prenatal androgen exposure or sensitivity and high prenatal testosterone levels.

Vivekananda and colleagues2 describe how they used 2D:4D as a surrogate for prenatal testosterone levels, hypothesising that reduced …

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  • Competing interests None.

  • Provenance and peer review Commissioned; not externally peer reviewed.

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