Читать книгу Genetic Disorders and the Fetus - Группа авторов - Страница 104

The AF disaccharidases have been used for the prenatal detection of fetal intestinal obstruction on the basis of low or absent activities in the AF.^{166, 186} Van Diggelen et al.¹⁸⁶ described a fetus with anal atresia at 17 weeks of gestation, and Dallaire and Perreault¹⁷⁶ studied 16 fetuses between 16 and 20 weeks with different types of intestinal obstruction, with or without ventral wall defects and chromosomal syndromes. In all of these cases, disaccharidase activities were abnormally low. The exclusively intestinal hydrolases maltase, sucrase, palatinase, and an intestinal form of alkaline phosphatase were the best markers for detecting intestinal obstruction.¹⁷² For the disaccharidase test to give valid results, the intestinal obstruction should hamper normal release of disaccharidases into the amniotic cavity. With multiple intestinal atresia the intestinal obstruction is complete, whereas with Hirschsprung disease the intestinal obstruction may be incomplete, thus permitting normal AF disaccharidase activities.¹⁸⁷

Low or absent disaccharidase activities, as well as alkaline phosphatase and α‐glutamyl transferase^{186, 188–191} have been reported in fetuses affected with CF. These fetuses seem to be unable to release their intestinal content normally into the amniotic cavity. It is important that the disaccharidase assay be performed no later than the 20th week because, after this period, some normal AF samples were found to have very low disaccharidase activities. The disaccharidase test gave false‐negative results in two fetuses with proven CF.¹⁸⁸ Six other fetuses with CF were deficient and were thus correctly identified retrospectively.¹⁷² Molecular diagnosis is now the standard (see Chapter 15).

The disaccharidase activities in AF are more specific to the fetal intestine and kidney than γ‐glutamyl transferase.^192–195 However, both α‐glutamyl transferase and alkaline phosphatase show reduced activity levels in the AF of various pathologic pregnancies, such as trisomy 18¹⁹² and 21.¹⁹³ Elevated activity of alkaline phosphatase has been observed in intrauterine fetal death, abdominal wall defect, Meckel syndrome, hydrops fetalis, and genital anomaly.¹⁸⁶ Elevated alkaline phosphatase activity in third‐trimester AF is often associated with fetal disorders.

Autosomal recessive villus atrophy syndrome is characterized by an atrophy of intestinal villi and reduced disaccharidase activities in the intestinal mucosa.¹⁹⁶ The disaccharidase activities would be expected to be low or deficient in the AF of an affected fetus. Normal disaccharidase activities in the AF were found in one case, and the newborn was subsequently noted to be phenotypically normal.¹⁷²

Trehalase activity in AF has been used to detect renal anomalies. Morin et al.¹⁶⁶ reported elevated trehalase/palatinase (or lactase) activity ratios in the AF of a fetus with polycystic kidney disease type II and two fetuses with congenital nephrotic syndrome of the Finnish type. These ratios were used as indices of the presence of renal trehalase in AF because palatinase and lactase are exclusively of intestinal origin.¹⁶⁶ Fetuses with renal congenital disease and degeneration of kidney tissue can be expected to release higher than normal levels of renal trehalase activity in the amniotic cavity.