REDUCED INFERIOR OLIVARY NEURON NUMBER IN EARLY DOWN-SYNDROME

Counts of total neuron number per section and of neurons per microscop ic field of inferior olivary principal nuclei were made on sections fr om 10 patients with Down syndrome (DS) aged 0.36 to 28 months and seve n control (C) patients aged 1 to 29 months. After stereologic and appr opriate shrinkage corrections of the count data, the ratios of values for DS/C were calculated. For mean principal olivary nucleus neuron nu mber, DS/C = 0.64; for mean number of neurons per field, DS/C = 0.84; for mean volume of olivary neuronal band per section, DS/C = 0.79; and for mean volume of neuronal band per neuron, DS/C = 1.27. The data ar e in accord with other data suggesting that (I) numbers of cells in va rious cell populations, including various areas of the cerebrum in DS approximate two-thirds normal (DS/C approximate to 0.67); (2) for two volumes of such cell populations, DS/C approximate to 0.82 normal; and (3) for volumes of individual cells, DS/C approximate to 1.22 normal. The data of the present study suggest that the inferior olivary nucle i in DS are affected in the same way and to a similar degree as other brain areas, with the age distribution and histologic features of the specimens studied suggesting that the reduced olivary principal nucleu s number in early Down syndrome results from reduced initial neuron pr oduction rather than postnatal neuron loss.