In twin-twin transfusion syndrome (TTTS), the disparity in circulation is r
eflected in discordant fetal growth, urine output, and amniotic fluid accum
ulation. The effect of uneven shunting of the growth factor and nutrient-ri
ch vasculature on development and differentiation of the kidney has not bee
n well studied. We analyzed renal tubular growth and differentiation in 25
fetal autopsies with TTTS (13 donors and 12 recipients, including 9 sibling
pairs) between 18 and 33 weeks gestation. Immunohistochemical markers for
fumarylacetoacetate hydrolase (FAR), Leu-Mi, and Lotus tetragonolobus (LTA)
were used to identify proximal convoluted tubules, and epithelial membrane
antigen (EMA) was used to demonstrate distal convoluted and collecting tub
ules. FAH appeared to be more specific and reliable than either Leu-Mi or L
TA in the identification of proximal tubules. Donors tended to demonstrate
a paucity of proximal tubules with crowding of glomeruli characteristic of
renal tubular dysgenesis (RTD). The degree of dysgenesis was greater in lat
er gestations and associated with more severe growth restriction. Donors in
TTTS are at risk for the development of RTD. Several authors suggest ische
mia as the underlying cause of "acquired" RTD. However, in this setting the
re is no evidence of cell death or necrosis, and we suggest that hypoperfus
ion leading to decreased glomerular filtration is the underlying etiology,
with the severity of RTD related to the degree of shunting.