Linkage studies exclude the AT-V gene(s) from the translocation breakpoints in an AT-V patient

An 8‐year‐old girl with severe microcephaly of prenatal onset, borderline intelligence, defects of skin pigmentation, deficiency of both humoral and cellular immunity, a normal serum α‐fetoprotein level and hypersensitivity to ionizing irradiation is described. Spontaneous chromosomal breakage in lymphocytes together with the clinical presentation led to the diagnosis of ataxia telangiectasia variant (AT‐V). In addition, the patient carried a constitutional translocation of paternal origin: 46,XX,t(3;7)(q12;q31.3) pat. In subsequent linkage and haplotype studies in 12 AT‐V families with microsatellite markers from each of the translocation breakpoint regions, we could clearly exclude the localization of an AT‐V gene to these regions.