Mosaic tetrasomy 8p is a rare chromosomal abnormality with a variable phenotypic spectrum. In the 14 cases described to date (Kristofferssonet al , 1988; Robinow etal, 1989; Fisher etal., 1993; Newton etal, 1993; Tilstraetal, 1993; Schrander-Stumpel et al, 1994; Lurie et al, 1995; Winters et al, 1995; Napoleone et al., 1997; Le Bris et al, 2003; Lopez-Pajares et al, 2003; Nucaro et al., 2006), defects in multiple organ systems were present, together with developmental delay and mental retardation. Here we describe a boy with agenesis of the corpus callosum (ACC) and subtle facial dysmorphism as the only identifiable features of mosaic tetrasomy 8p. Unlike other patients, he exhibits age-appropriate development to date. A review of the literature shows that this broadening of the phenotype does not relate to the prevalence of this accessory chromosome in circulating lymphocytes, and reflects the inherent difficulty in the identification of mosaic disorders, particularly in terms of prenatal diagnosis.
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