Monozygotic twin girls with congenital malformations resembling fanconi anemia.

Monozygotic (MZ) twin girls, diagnosed at birth to have Fanconi anemia (FA) on the basis of multiple anomalies and an apparently increased baseline chromosomal breakage frequency in one twin, have been followed prospectively for 13 years. They have not developed aplastic anemia or other hematologic manifestations of FA. There was no evidence for increased baseline or diepoxybutane (DEB)-induced chromosomal breakage in either twin when the studies were repeated in Denver as well as in New York. Since the cellular phenotype must be considered in establishing the diagnosis of FA, these MZ twins should not be classified as affected with FA. Using the scoring system for FA diagnosis developed by Auerbach et al. [1989], the probability coefficients of their having FA based solely on clinical findings, prior to DEB testing, were .75 and .92, respectively. When the combination of their anomalies are taken together, their FA probability coefficient is .98. Through the International FA Registry, 15 additional patients have been identified with an FA probability score of .75 or greater, but who have not developed aplastic anemia and who are DEB negative. These patients, as well as the twins described in this report, are most likely a heterogeneous group and may represent other syndromes like Holt-Oram, VATER, VACTERL and IVIC, with genetic as well as nongenetic etiologies. These cases demonstrate the importance of testing with DEB or other DNA crosslinking agent in order to discriminate between FA and other syndromes with a similar phenotype.