Agenesis

AGENESIS (from the Greek a- negative particle, and genesis-origin, formation), absence of development (syn. aplasia), a term used to denote a deformity consisting of the complete congenital absence of one or another organ, part of it, or part of the body. Examples of A. may be A. of the kidney, testicle, thyroid gland, certain limbs. (Causes of A.-see Deformities.) The consequences of A. are diverse: in A. of one of the paired organs or part of an organ, compensatory hypertrophy (see) of the properly developed part develops, compensating for the function of the undeveloped one, as a result of which in such cases there may be no harmful consequences of A.; A. of certain unpaired organs or their parts (e.g., brain, heart) or both paired organs (e.g., kidneys) may underlie the non-viability of the fetus; finally, A. of one or another organ during life may be accompanied by symptoms of loss of function of the absent organ [e.g., congenital myxedema (see) with agenesis of the thyroid gland].