In this report, we examine a variety of patient fibroblasts, including those from 3 patients with MAD-B due to mutations in ZMPSTE24 (P248L and L425P) and those from patients with atypical progeroid syndromes (APS) whose mutations map in LMNA (D325N, M540T, C558R, and E138K), but at a distance from the processing site. The gene discussed is ZMPSTE24; the disease is mandibuloacral dysplasia with type B lipodystrophy.