C-Type Natriuretic Peptide (CNP) levels are altered in boys with Klinefelter syndrome.

B-type natriuretic peptide (BNP) expression in vitro is up-regulated by the protein coded by the short stature homeobox gene (SHOX). C-type natriuretic peptide (CNP) is a paracrine regulatory factor of the growth plate that plays a key role in endochondral growth and shares clearance pathways with BNP. We explored the possibility that alterations in natriuretic peptide regulation may play a role in the overgrowth of boys with Klinefelter syndrome.,The objectives of the study were to document the blood levels of amino-terminal propeptide of B-type natriuretic peptide (NTproBNP), CNP, and its amino-terminal propeptide (NTproCNP) in boys with Klinefelter syndrome and compare values with age- and height-matched control subjects.,This was a prospective, case-controlled, observational study.,Participants were 24 healthy boys with Klinefelter syndrome between 4 and 14 yr of age. Data from sex-, age-, and height-matched healthy controls were obtained from subjects participating in a previously described study.,Plasma levels of NTproBNP and CNP were lower, whereas levels of NTproCNP were higher in boys with Klinefelter syndrome compared with published reference ranges. In addition, CNP levels were lower and NTproCNP levels higher than in sex-, age-, and height-matched controls.,In contrast to plasma NTproBNP, CNP production and clearance are increased in boys with Klinefelter syndrome. Together these findings argue against an interaction between BNP with CNP in the growth plate. Why CNP peptide levels are altered in Klinefelter syndrome remains to be explored.