Bartter syndrome involves an overlapping set of closely related renal tubular 
disorders which can be subdivided into at least three clinical phenotypes: (1) 
classic Bartter syndrome (2) Gitelman syndrome, and (3) a neonatal variant of 
Bartter syndrome. In contrast to classic Bartter syndrome and Gitelman syndrome, 
the neonatal variant of Bartter syndrome has both the features of renal tubular 
hypokalemic alkalosis as well as profound systemic manifestations. Specifically, 
neonatal Bartter syndrome is characterized by intrauterine polyhydramnios, 
premature delivery, and life-threatening episodes of fever and dehydration. Most 
of these infants also have severe hypercalciuria with associated 
nephrocalcinosis and osteopenia. Over a 22-year period, 20 Costa Rican patients 
with a congenital syndrome that resembles neonatal Bartter syndrome have been 
identified and characterized. While these patients exhibit some of the clinical 
characteristics previously described for neonatal Bartter syndrome, this cohort 
also has a set of distinct features. They are predominantly female, have a later 
age of diagnosis, manifest a relatively unique set of physical traits, and 
appear to have milder clinical disease. Given these differences, it will be 
important to apply the emerging molecular tools to determine whether the 
phenotypic variability indicates genetic heterogeneity in neonatal-onset Bartter 
syndrome.