Frequent occurrence of a zeta-globin-region deletion in American blacks accounts for a previously-described restriction site polymorphism.

We describe an 11.3 kb deletion within the zeta-globin gene region which was found in 2 of 16 American Black neonates. The deletion is consistent with an unequal crossover between the homologous zeta and psi zeta gene regions, resulting in a shortened Eco RI fragment (17.2 kb) containing a single zeta and the psi alpha, alpha 2, and alpha 1 genes. An earlier report of zeta-region crossovers (1) may have overestimated the size of this fragment by 2 kb. This finding led us to re-evaluate another report which concluded that a 17 kb Eco RI fragment found in 10% of the Black population was the result of a restriction site polymorphism (2). Our data do not substantiate this conclusion and we propose that the high frequency of this shortened fragment is due instead to an unequal crossover. Possible clinical consequences of this deletional event are also discussed.