Effects of Growth Hormone on Cognition and Cerebral Metabolism in Adults With Growth Hormone Deficiency

Eligibility screening: Diagnosis of GHD will be based on standard testing, including a blunted GH response to stimulation with glucagon provocation, defined as GH \<3 microgram/l. Subjects with adult-onset GH deficiency will be included if they are age 18-65 years old, naive to GH replacement therapy, in good general health, and on stable thyroid, glucocorticoid (at replacement doses) and gonadal replacement therapy for at least 6 weeks prior to study initiation. Patients with history a Major Depression will be excluded. Baseline: Qualifying subjects will be admitted to the CTRU for the following: Weight, body mass index, waist/hip ratio, menstrual cycle history on female subjects and vital signs. Initial clinical laboratory assessments will include IGF-1, a complete blood count, liver function tests, free T4, and a serum pregnancy test for women. Subjects will undergo 3 hours of neuropsychological testing when attention, working memory, executive function and verbal memory will be assessed with the Wechsler Adult Intelligence Scale III and Wechsler Memory Scale (WMS III). Quality of life and mood will be quantified through the Quality of Life Scale, Hamilton Rating Scale for Depression and the Quality of Life Assessment of Growth Hormone Deficiency in Adults (Qol AGHDA). After a lunch break, the patients will undergo a 1 hour MRI scan. Resting images will be obtained, and thereafter simple letters, words or pictures will be projected to subjects while in the scanner. The subjects will be asked simple questions relating to these stimuli. Randomization and treatment: Following completion of the baseline measurements, study participants will be randomized in a double blind fashion to receive either active treatment with GH or placebo for a period of 16 weeks. GH dosages will be increased incrementally over the first 6 weeks. At 16 weeks, all subjects randomized to placebo will be switched to GH in an open label fashion with dose schedules based on the above titration. Subjects initially randomized to GH will continue to receive GH with their endocrinologist without further follow up for the study. For efficacy measures, neuropsychological testing and fMRI will be performed at baseline and at 16 weeks, and, for subjects initially randomized to placebo, repeat studies will be performed at 32 weeks. Safety monitoring will include assessment of changes in thyroid and adrenal status, as well as changes in liver function.