Age-Related Sexual Dimorphism in Temporal Discrimination and in Adult-Onset Dystonia Suggests GABAergic Mechanisms.

John S Butler,Dan G Healy,Richard B Reilly,Seán O’Riordan,Michael Hutchinson,Tim Lynch,Richard Walsh,Ines M Beiser,Laura Williams,Cathal Walsh,Eavan Mcgovern,Helena Moore,Fiona Molloy

doi:10.3389/fneur.2015.00258

Abstract

Adult-onset isolated focal dystonia (AOIFD) presenting in early adult life is more frequent in men, whereas in middle age it is female predominant. Temporal discrimination, an endophenotype of adult-onset idiopathic isolated focal dystonia, shows evidence of sexual dimorphism in healthy participants. We assessed the distinctive features of age-related sexual dimorphism of (i) sex ratios in dystonia phenotypes and (ii) sexual dimorphism in temporal discrimination in unaffected relatives of cervical dystonia patients. We performed (i) a meta-regression analysis of the proportion of men in published cohorts of phenotypes of adult-onset dystonia in relation to their mean age of onset and (ii) an analysis of temporal discrimination thresholds in 220 unaffected first-degree relatives (125 women) of cervical dystonia patients. In 53 studies of dystonia phenotypes, the proportion of men showed a highly significant negative association with mean age of onset (p < 0.0001, pseudo-R (2) = 59.6%), with increasing female predominance from 40 years of age. Age of onset and phenotype together explained 92.8% of the variance in proportion of men. Temporal discrimination in relatives under the age of 35 years is faster in women than men but the age-related rate of deterioration in women is twice that of men; after 45 years of age, men have faster temporal discrimination than women. Temporal discrimination in unaffected relatives of cervical dystonia patients and sex ratios in adult-onset dystonia phenotypes show similar patterns of age-related sexual dimorphism. Such age-related sexual dimorphism in temporal discrimination and adult-onset focal dystonia may reflect common underlying mechanisms. Cerebral GABA levels have been reported to show similar age-related sexual dimorphism in healthy participants and may be the mechanism underlying the observed age-related sexual dimorphism in temporal discrimination and the sex ratios in AOIFD.

Highlights

Twenty years ago, a paper from the late David Marsden’s research group, reporting on the sex ratios of the phenotypes of adult-onset dystonia, concluded by stating: “Our study confirms a clear but mild preponderance of females with various types of craniocervical dystonia and of males with writer’s cramp
A phenotypic difference between males and females of the same species, in temporal discrimination is age dependent; the initial advantage of the young adult woman is lost and reversed in middle age. We further examine this sexual dimorphism in temporal discrimination in a large group of unaffected first-degree relatives of cervical dystonia patients
We examine by meta-analysis the relationship between mean age of onset and sex ratios in published cohorts of adult-onset isolated focal dystonia (AOIFD) phenotypes

Summary

Introduction

A paper from the late David Marsden’s research group, reporting on the sex ratios of the phenotypes of adult-onset dystonia, concluded by stating: “Our study confirms a clear but mild preponderance of females with various types of craniocervical dystonia and of males with writer’s cramp. Why this is so remains to be discovered” [1]. Adult-onset isolated focal dystonia (AOIFD) presenting in early adult life is more frequent in men, whereas in middle age it is female predominant. An endophenotype of adult-onset idiopathic isolated focal dystonia, shows evidence of sexual dimorphism in healthy participants

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