Antenatal development of amylase isoenzymes.

Relatively little is known about the normal physiology of amniotic fluid, its dynamics, and its constituent enzymes and isoenzymes. The antenatal diagnosis of some metabolic errors is frequently based upon the investigation for the presence or absence of an enzyme in the amniotic fluid or cells. In establishing an antenatal diagnosis of this kind, it is essential that 2 major factors be borne in mind: (1) During fetal development and, indeed, during the first months of life, an enzyme may not be present in normal circumstances and its absence is of no prognostic or diagnostic value. (2) If an enzyme is present during fetal development, it may only be represented by some of its isoenzymatic forms, not by its phenotypical appearance and function as recognized later in life. This can influence, both quantitatively and qualitatively, a prenatal diagnosis, possibly in the wrong direction. The purpose of the present study was to investigate the dynamics of such an enzyme, namely, of alpha-amylase (alpha-i, 4-glucan 4 glucanohydrolase) during fetal development, by subjecting amniotic fluid at various stages of pregnancy to the electrophoretic technique used for amylase detection and separation. Previous studies have revealed the presence of 2 polymorphisms controlled by 2 (possibly 3) loci one controlling pancreatic amylase secretion and the other salivary amylase secretion. Other previous investigations, based on the study of 100 infants, followed monthly from birth to 12 months, have shown that, postnatally, pancreatic activity develops more slowly than salivary activity and the complete phenotype, as observed in the electrophoretic pattern of serum or urine of older children and adults, is not usually present until approximately the 12th to 14th month of life. The curve of development of each fraction, with age, is demonstrated in Fig. 1 (Kamaryt and Fintajslova, 1971).