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To the Editor:
—Dr. Klein raises an interesting and important point which I correctly but neatly sidestepped in my previous reply. This is the distinction between a mental defective (oligophrenic) and mental retardation. When Dr. Klein states that I indicate that schizophrenia may result in mental retardation, this is precisely the case. By mental retardation I very clearly mean the retarding of mental processes, regardless of the cause. There is a considerable literature on this subject including differential diagnosis (Bender, Kanner, Fish, Eisenberg, Goldfarb, etc.). Oligophrenia constitutes one type of mental retardation and, in the given case histories of the twins, the fact that presumably they developed normally until the age of 4 yr specifically rules out congenital oligophrenia. The coexistence of oligophrenia and schizophrenia has long been recognized and is described in the European literature under the term "propf schizophrenia."I would further concur that clear delineation of diagnostic
Kline NS. Mental Retardation and Schizophrenia. JAMA. 1963;184(2):163. doi:10.1001/jama.1963.03700150117033