Following reference to the reciprocal nature of syndromes associated with del(5p) and dup(5p) (Lejeune et al., 1964b), the concept of type and countertype (contre-type) was proposed by Lejeune et al. (1964a) to describe what they believed to be the opposing physical and physiological effects of trisomy 21 and monosomy 21 (actually complete and mosaic partial monosomy 21). They were impressed by certain striking and opposing phenotypic characteristics in the latter two syndromes – such as the slant of the eyes, the tone of the muscles, the configuration of the nasal bridge (Table 8.1). Reference was made to the existence of Drosophila with triplo-IV and haplo-IV, which were said to furnish the classic example of type and countertype. [However, this is probably not the case since haplo-IV flies have numerous somatic abnormalities (Bridges, 1921), while the triplo-IV are hard to distinguish from ordinary diploids (Hochman, 1976)].

The monosomy 21 or del(21) syndrome later came to be known as antimongolism (Reisman et al., 1966), conjuring up the image that the trisomic and monosomic phenotypes had a large number of complementary or opposite phenotypic characters. From antimongolism, the term “antisyndrome” evolved as a synonym for countertype. Following the initial description, the concept, however named, was then extended to cover abnormalities of chromosome arms 5p and 18q (Lejeune et al., 1964b; Lejeune, 1966), and then 13q (Lejeune et al., 1968), 4p (Rethoré et al., 1974), 9p (Hernandez et al., 1979b), 10qter (Turleau et al., 1979), and 12p (Rethoré et al., 1975).