Beginning with the writings of Esquirol (1838), who provided the first description of a child with Down syndrome, and John Langdon Down, whose article “Observations on an Ethnic Classification of Idiots” (1866) describes some of the characteristics of the children who are his namesakes, theorizing and research about Down syndrome have proliferated in the scientific literature (see Booth, 1985; Gibson, 1978; and Rynders & Pueschel, 1982, for historical reviews). Although earlier explorations into unraveling the complexities of this condition were conducted primarily by researchers interested in its biomedical aspects, increasingly the study of Down syndrome has become a multidisciplinary endeavor. As the most common organic form of mental retardation, it is not surprising that Down syndrome has captured the attention of so many talented research investigators, educators, and clinicians.
Down syndrome occurs in approximately 1 out of every 600 live births (Hook, 1982), resulting in nearly 7,000 infants in the United States and 1,000 in the United Kingdom born with Down syndrome each year (Wishart, 1988). Down syndrome arises from an abnormality on chromosome 21 (Thuline & Pueschel, 1982). Chromosome pair 21 is the smallest of the 23 human chromosome pairs, possessing only about 1.5% of the total genetic material. Moreover, gene-mapping studies have revealed that only 10% to 20% of chromosome 21, the 21q 22 band on the long arm, is involved in Down syndrome (Patterson, 1987a, 1987b; Patterson et al., 1985; Smith, 1985). Nonetheless, the presence of an additional copy of this small chromosome exerts a profound impact on the developmental biology and psychology of Down syndrome (Benda, 1960, 1969; Breg, 1977; Cicchetti & Ganiban, in press; Cicchetti & Pogge-Hesse, 1982; Coyle, Oster-Granite, & Gearhart, 1986; Epstein, 1986; Lane & Stratford, 1985; Nadel, 1988; Penrose & Smith, 1966; Pueschel & Rynders, 1982; Smith & Berg, 1976)