Results Clinical findings are summarized in Table I, and presented in detail in the case reports. Of 46 features scored, 44 occur in both syndromes, a considerable degree of overlap. An attempt has been made to measure this overlap: the right-hand column of Table I gives the discriminating ratio, which is calculated as the percentage of Edwards' syndrome cases with featuresdivided by the percentage of Patau's cases with the same features. Taking two arbitrary cut-off points at ratios< 0 5 and> 1-5, it is possible to separate'Patau's' features, an area of major overlap, and'Edwards" features. Features separated in this fashion are presented in Table II.