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Giemsa banding pattern of a heritable 1q+ variant chromosome: a possible partial duplication.

One morphological variant of chromosome 1 in man differs from the more usual form of this chromosome in being longer and more submetacentric. This is due to increased length of the long arm and because there is apposition of chromatids in the paracentromeric region of the long arm (q). This variant, or similar appearing variants ofchromosome 1, have been found in 1 per 100 to 1 per 1000 newborns in the United States (Lubs and Ruddle, 1971). Previous studies have reported lq + variants in individuals with a variety of anomalies as well as in phenotypically normal individuals (Cooper and Hernits, 1963; Donahue et al, 1968). Since the same anomaly has never been associated with the variant chromosome in more than one instance, and since phenotypically normal individuals have also been reported carrying the variant chromosome, it can be concluded that it is a normal variant which causes no obvious phenotypic abnormality. Family studies of 1 q + variants have, together with gene linkage studies, served to assign a series of genes to chromosome 1. These include the loci for the Duffy blood group (Donahue et al, 1968; Ying and Ives, 1968), congenital pulverulant cataract (Renwick and Lawler, 1963/1964), and amylase 2 (Karamyt, Adaimek, and Vrba, 1971; Hill, Rowe, and Lovrien, 1972). We investigated a 3-generation Caucasian family with a variant chromosome 1 (Fig. 1). The proposita was originally ascertained because of mild mental retardation but had no physical anomalies. Other members of the family were phenotypically normal. We designed studies (1) to determine the effect of the hypotonic treatment upon the appearance of the variant; and (2) to learn if the apparent increase in length was due to uncoiling or to the addition of chromosomal material to lq.