Open-label Comparison of Chronocort® Versus Standard Glucocorticoid Replacement Therapy

Inclusion Criteria: Participants are eligible to be included in the study only if all of the following criteriaapply (note: if a participant fails to meet an inclusion criterion, re-screening ispermitted if the Investigator considers that the circumstances leading to screening failurewill not be relevant when the participant is re-screened at a later time): Age

1. Participant must be aged 16 years or older at the time of signing the informedconsent.
2. In participants aged <18 years, height velocity must be less than 2 cm in the lastyear and puberty must be completed. Type of Participant and Disease Characteristics
3. Participants with known CAH due to 21-hydroxylase deficiency (classic CAH) diagnosedin childhood with documented (at any time) elevated 17-OHP or A4 and currently treatedwith hydrocortisone, prednisone, prednisolone or dexamethasone (or a combination ofthe aforementioned glucocorticoids). Sex
4. Male and female participants
5. Male participants:

• A male participant must agree to use contraception as detailed in Section 10.4of this protocol during the treatment period and refrain from donating spermduring this period.

2. Female participants:

• A female participant is eligible to participate if she is not pregnant (Section 10.4), not breastfeeding, and at least one of the followingconditions applies: i. Not a woman of childbearing potential (WOCBP) as defined in Section 10.4. OR ii. AWOCBP with a negative pregnancy test at entry into the study who agrees to follow thecontraceptive guidance in Section 10.4 during the treatment period. Note: females presenting with oligomenorrhea or amenorrhea who are aged ≤55 yearsshould be considered potentially fertile and therefore, as well as undergoingpregnancy testing like all other female participants, will be expected to be using anacceptable method of contraception which should have been ongoing for ≥90 days priorto the study. Informed Consent

5. Capable of giving signed informed consent as described in Section 10.1 which includescompliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol.

Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply (note: if aparticipant meets an exclusion criterion, re-screening is permitted if the Investigatorconsiders that the circumstances leading to screening failure will not be relevant when theparticipant is re-screened at a later time): Medical Conditions

1. Clinical or biochemical evidence of hepatic or renal disease e.g. creatinine > 2 timesthe upper limit of normal (ULN) or elevated liver function tests (alanineaminotransferase [ALT] or aspartate aminotransferase [AST] >2 times the ULN).
2. History of bilateral adrenalectomy.
3. History of malignancy (other than basal cell carcinoma successfully treated >26 weeksprior to entry into the study).
4. Participants who have type 1 diabetes or any participant who is receiving insulin.
5. Participants with any other significant medical or psychiatric conditions that in theopinion of the Investigator would preclude participation in the study. Prior/Concomitant Therapy
6. Participants on regular daily oral steroids for any indication other than CAH. Note: aparticipant should not be given any steroids (even on an irregular basis) within 5days of a study visit. If there is a medical need for steroid treatment within thistime frame then the visit should be postponed until a 5-day interval has elapsed.
7. Co-morbid condition requiring daily administration of a medication or consumption ofany material that interferes with the metabolism of glucocorticoids (examples providedat http://medicine.iupui.edu/clinpharm/ddis/clinical-table/).
8. Participants who are receiving <10 mg hydrocortisone dose at baseline or thehydrocortisone dose equivalent. Prior/Concurrent Clinical Study Experience
9. Participation in another clinical study of an investigational or licensed drug ordevice within the 12 weeks prior to screening or during the study.
10. Inclusion in any natural history or translational research study that would requireevaluation of androgen levels during the study period outside of this study protocolassessments.
11. Participants who have previously been exposed to Chronocort in studies DIUR-003,DIUR-005 or DIUR-006. Other Exclusions
12. Participants who routinely work night shifts and so do not sleep during the usualnight-time hours.
13. Participants unable to comply with the requirements of the protocol.