Proposed is a mechanism through which exposure in utero to deleterious agents (including radiation) induces hereditary nervous (and immune) deficiencies in newborns. This mechanism was found theoretically in the framework of multidisciplinary analysis of neuroimmunoendocrine reactivity development peculiar to normal embryogenesis in comparison to that under in utero exposure. Found systemic mechanism accounts induced neural (and or) immune reactivity deficiencies on the response of embryonic homeostasis to effects of radiation or any other deleterious agent on growth potencies of embryo cells. Paradoxically, in the frame of the theory, this homeostatic response appears adverse to normal development of nervous (and immune) reactivity of a newborn after in utero exposure. Therefore, well known phenomenon of "overall" susceptibility of nervous and immune reactivity of a newborn to in utero action of a vast majority of harmful agents has met its first elucidation. Proposed theory of a "systemic teratogenesis" is in accordance with known specific endocrine grounds of nervous diseases. It also prognosticates the existence of systemic effects on nervous and immune reactivity resulting from radiation exposure at preimplantation stage of embryogenesis. Such effects were never observed before. Thus, the theoretically founded mechanism appears quite verifiable in the frame of proper animal experiments.