Validation of Macimorelin as a Test for Adult Growth Hormone Deficiency

Inclusion Criteria: * Suspected growth hormone deficiency (GHD), based on either of the following: * structural hypothalamic or pituitary disease, or * surgery or irradiation in these areas, or * head trauma as an adult, or * evidence of other pituitary hormone deficiencies, or * idiopathic childhood onset GHD (without known hypothalamic or pituitary lesion or injury). * Healthy\* control subjects, matching a 'high likelihood GHD' subjects Exclusion Criteria: * GH therapy within 1 month prior to anticipated first GHST within this trial (within 3 months in case of long-acting GH formulation). * GHST within 7 days prior to the anticipated first test day within the trial. * Subjects with a medical history and clinical signs of a not adequately treated thyroid dysfunction or subjects who had a change in thyroid therapy within 30 days prior to anticipated first test day within the trial. * Untreated hypogonadism or not on a stable substitution treatment within 30 days prior to anticipated first test day within the trial. * Treatment with drugs directly affecting the pituitary secretion of somatotropin (e.g. somatostatin analogues, clonidine, levodopa, and dopamine agonists) or provoking the release of somatostatin; antimuscarinic agents (atropine). * Concomitant use of a CYP3A4 inducer (e.g., carbamazepine, phenobarbital, phenytoin, pioglitazone, rifabutin, rifampin, St. John's Wort). * Medical history of ongoing clinically symptomatic severe psychiatric disorders. * Parkinson's disease. * Cushing disease or patients on supraphysiologic glucocorticoid therapy within 30 days prior to the anticipated first test day within the trial. * Type 1 diabetes or untreated or poorly controlled Type 2 diabetes, as defined by HbA1c \> 8%. * Body mass index (BMI) ≥ 40.0 kg/m2. * Participation in a trial with any investigational drug within 30 days prior to trial entry. * Vigorous physical exercise within 24 hours prior to each GHST within this trial. * Known hypersensitivity to macimorelin or insulin, or any of the constituents of either preparation. * Clinically significant cardiovascular or cerebrovascular disease. * Prolonged ECG QT interval, defined as corrected QT interval (QTc) \> 500 msec. * Concomitant treatment with any drugs that might prolong QT/QTc. * Elevation of laboratory parameters indicating hepatic or renal dysfunction or damage (aspartate amino transferase (ASAT), alanine aminotransferase (ALAT), gamma-glutamyl transpeptidase (GGT)\> 2.5 x ULN; ), creatinine, or bilirubin \> 1.5x ULN). * Medical history of seizure disorders. * Known immunosuppression. * Current active malignancy other than non-melanoma skin cancer. * Breastfeeding or positive urine pregnancy test (for women of childbearing potential only). * Women of childbearing age without contraception, such as hormonal contraception or use of condom and spermicides or use of diaphragm and spermicides or Intra Uterine Device (IUD). * Lack of ability or willingness to give informed consent. * Anticipated non-availability for trial visits/procedures.