A Study in Pediatric Participants with Congenital Adrenal Hyperplasia

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• Part A and Part B: Individuals in Part A and Part B who meet any of the following criteria will be excluded from participation in this study: 1. Diagnosis of any form of CAH other than classic 21-OHD. 2. Participants treated with other GC formulations within 30 days of Screening. 3. Stress dose of GC therapy within 2 weeks of start of Screening, defined as any dose above the normal maintenance dose, including but not limited to IV or IM hydrocortisone. 4. Use of growth hormones within 1 week of start of Screening for short acting, or within 6 weeks of start of Screening for long acting. 5. Use of a corticotropin-releasing factor receptor antagonist within 14 days of Screening.
• 6. Participants with any clinically significant abnormal laboratory test during Screening or clinically significant concomitant disease other than CAH including but not limited to cardiovascular disease; moderate or severe renal insufficiency (estimated glomerular filtration rate <60 mL/min/1.73 m2 using CKD-EPI formula) at Screening; or Significant liver disease or ALT and/or AST >3×ULN, and/or TBil >1.5×ULN during Screening. TBil >1.5×ULN (Participants with Gilbert’s syndrome can be included with TBil >1.5×ULN as long as direct bilirubin is ≤1.5×ULN AND <35% of TBil) 7. History of bilateral adrenalectomy, hypopituitarism, or other condition requiring chronic GC therapy. 8. Participants with any clinically significant abnormal laboratory test during Screening or clinically significant concomitant disease other than CAH including but not limited to cardiovascular disease (defined as any condition that affects the heart’s structure, function, or electrical system, regardless of stage of disease); moderate or severe renal insufficiency (estimated glomerular filtration rate <60 mL/min/1.73 m2 using the Bedside Schwartz Equation)) at Screening; or Significant liver disease or ALT and/or AST >3×ULN, and/or TBil >1.5×ULN during Screening. TBil >1.5×ULN (Participants with Gilbert’s syndrome can be included with TBil >1.5×ULN as long as direct bilirubin is ≤1.5×ULN AND <35% of TBil).. 9. Poorly controlled diabetes mellitus as judged by the Investigator. 10. Participants with hypothyroidism who are not receiving adequate hormone replacement therapy based on thyroid hormone levels measured at the time of Screening, as determined by the Investigator.
• 11. History of cancer excluding cured/treated dermal squamous or basal cell carcinoma or cervical carcinoma in situ. 12. ECG: a. Ages 12 to <18: QTcF interval >450 msec (males) or >470 msec (females), PR interval >220 msec, QRS interval >120 msec, second- or third-degree atrioventricular block, left bundle branch block, or hemiblock at Screening. b. Ages 1 to 11: Anything abnormal, even if not clinically significant, is an exclusion. A cardiologist can override a machine reading. 13. Abnormal sleep/wake cycles (as determined by the Investigator). 14. Participants with known history of (that is within the past 12 months) or current alcohol or drug abuse. Participants that are abusing, in the opinion of the Investigator, cannabis, tobacco, and/or the use of e-cigarettes (vaping). 15. Participants with any mental condition rendering him/her unable to understand the nature, scope, and possible consequences of the study, and/or evidence of poor compliance with medical instructions.
• 16. Participants with a known allergy or hypersensitivity to any of the test materials or related compounds, including being at high risk of adrenal insufficiency as judged by the Investigator. 17. Female participants who are pregnant or lactating. 18. An employee or immediate family member of an employee of Crinetics. 19. Participants who have been dosed with an investigational drug (other than atumelnant) in any prior clinical study within 60 days or 5 half-lives (whichever is longer) prior to the first dose. Part C: 20. Individuals in Part C who do not meet the Part C Inclusion Criteria