GH1 and isolated congenital growth hormone deficiency: As the National Cooperative Growth Study (NCGS) database now contains 220,000 patient-years of growth data on children receiving recombinant human growth hormone (rhGH) therapy, we asked the following questions: 1) Does exogenous rhGH obscure “seasonal” variability in height velocity (HV) in prepubertal children with isolated growth hormone deficiency (IGHD) in North America?