Ribosomal subunit association is impaired in SDS patient cells. (A) Bone marrow stromal cells or (B) lymphoblasts from healthy controls or SDS patients were lysed in 0.25mM MgCl₂ to dissociate the 40S and 60S ribosomal subunits (left panels). MgCl₂ was added (+Mg →) to an aliquot of each lysate to test the ability of the 40S and 60S ribosomal subunits to form 80S monomers (right panels). The resulting ribosomal profiles were analyzed by sucrose gradient sedimentation. Representative assays are shown. The resulting 80S:40S ratios were quantitated for 3 healthy controls versus 4 SDS patients of different SBDS genotypes as noted in the text; *P < .05.