Sunday, June 04, 2006

The 13 Year Window

The premise brought forth (Nicolaou and Templeton, 2003Go) is that there is a 13-year window between the beginning of the accelerated phase of atresia (38 years) and the average age of menopause (51 years).

Nikolaou, D. and Templeton, A. (2003) Early ovarian ageing: a hypothesis. Detection and clinical relevance. Hum. Reprod., 18, 1137–1139

There are two general concerns challenging this hypothesis.....

The second issue is the ‘fixed’ nature of this window of 13 years. Basically, we just do not know if this is the case. While it was originally assumed that oocyte loss occurred as a constant logarithmic function (Block, 1952Go), it is more accepted now that there is an accelerated depletion after age 38 years (Richardson et al., 1987Go; Gougeon et al., 1994Go).

Block, E. (1952) Quantitative morphological investigation of the follicular system in women. Acta Anat., 14, 108–123

Richardson, S.J., Senikas, V. and Nelson, J.F. (1987) Follicular depletion during the menopausal transition. Evidence for accelerated loss and ultimate exhaustion. J. Clin. Endocrinol. Metab., 65, 1231–1237

Gougeon, A., Ecochard, R. and Thalabard, J.C. (1994) Age-related changes of the population of human ovarian follicles: Increase in the disappearance rate of non-growing and early-growing follicles in aging women. Biol. Reprod., 50, 653–663.

However, it is not at all clear what the variability is in the slope of this line. Rate of atresia may be variable in different women, and this variability may occur before age 38, as well as in the time period after age 38. At least two conditions have been theorized to alter (increase) the rate of atresia (genetic variations in the X chromosome and thymectomy) (Singh and Carr, 1966Go; Lintern-Moore, 1977Go)

The 13-year window (which is assumed to be the average time frame for women) may not be 13 years per se and is likely to be less or more on an individual basis.

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