A chromosomal breakpoint that separates the esterase D and retinoblastoma predisposition loci in a patient with del(13)(q14q31).

A patient with severe mental retardation and other congenital abnormalities who developed retinoblastoma was shown to have a deletion on the long arm of chromosome #13 with breakpoints in regions q14 and q31. Quantitation of enzyme activity of the esterase-D gene which, together with the retinoblastoma locus, is located in region 13q14 showed levels that were equal to those of normal controls. The 13q14 breakpoint, therefore, appears to have occurred between the two loci, which places the esterase D gene in a more proximal position in this band than the retinoblastoma locus.