Cytogenetic studies in Wiskott-Aldrich syndrome: identification of a case with a 6p chromosome abnormality.

Lymphocytes from patients with Wiskott-Aldrich syndrome (WAS) were studied with prometaphase G banding to search for minor chromosome anomalies and in mutagen stress assays to assess the extent of chromosome breakage under these conditions. One patient, a sporadic case of WAS, was found to have a stable inversion of a large segment of one chromosome 6 that involved the region encoding the major histocompatibility complex (MHC). The anomaly was not present in the patient's parents, nor in three other unrelated patients with WAS, all of whom demonstrated X-linked inheritance (based on family history). None of the four patients showed an excessive number of breaks or radial exchange figures following exposure to mitomycin C or diepoxybutane. Thus chromosome fragility in WAS was not confirmed by these studies. However, the incidental finding of 6p inversion in a sporadic case of WAS suggests that genetic rearrangement involving the MHC can result in clinical immunodeficiency mimicking WAS.