Hyaluronan in the nuchal skin of chromosomally abnormal fetuses

Nuchal skin oedema at 10-14 weeks gestation, observed by ultrasonography as increased nuchal translucency (NT), is found in similar to 70% of fetuses with trisomies 21, 18 and 13 as well as those with Turner's syndrome. This study investigates the possibility that one mechanism for increased translu cency is an altered composition of the skin with a higher concentration of hyaluronan; large amounts of hyaluronan can lead to excessive hydration of the extracellular matrix. We isolated the hyaluronic acid binding region (H ABR) from aggrecan in the extracellular matrix of hyaline cartilage and use d it in a biotinylated form in combination with a fluorescent probe as a ma rker for hyaluronan. Immunohistochemistry was then used to examine the nuch al skin of chromosomally abnormal and normal fetuses, obtained after termin ation of pregnancy. In fetuses with trisomy 21 there was a substantial incr ease in hyaluronan, whereas in trisomies 18 and 13 and Turner's syndrome th e amount was similar to that in chromosomally normal controls. This finding suggests that hyaluronan may be implicated in the pathogenesis of increase d NT in fetuses with trisomy 21, but the common phenotypic expression of in creased translucency in different chromosomal abnormalities may be the cons equence of other mechanisms.