Congenital adrenal hyperplasia (CAH) is a group of inherited disorders present from birth that affect hormone production in the adrenal glands. It arises when an enzyme deficit limits cortisol output, so the gland enlarges in response to altered signalling.
The condition varies in severity: some people have mild forms, while others face life‑threatening shortages of salt and sugar in infancy. Early recognition is therefore vital, as prompt treatment helps the body cope with stress and prevents dangerous complications.
This Ultimate Guide will outline the main causes, common symptoms and typical diagnostic and treatment pathways used in the UK. It also explains why CAH is a spectrum disorder and how signs can affect salt balance, growth, puberty timing and genital development. Readers will find age‑specific information and practical advice for families and clinicians.
Key Takeaways
- CAH is an inherited group of disorders that disrupt cortisol production and can enlarge the gland.
- Early detection matters: some forms can become rapidly life‑threatening in newborns.
- Signs often involve salt balance, blood sugar, growth and puberty timing.
- Severity depends on which enzyme is affected and the degree of deficiency.
- The guide covers causes, symptoms, diagnosis and UK treatment pathways.
What congenital adrenal hyperplasia is and why it matters
CAH describes a group of inherited disorders present from birth that affect how the adrenal glands make key steroids.
CAH as a group of inherited conditions present from birth
In these inherited conditions the body is missing an enzyme needed for normal steroid production. This enzyme fault is present at birth and alters the balance of several hormones.
How adrenal hyperplasia develops when cortisol is not made properly
When cortisol falls, the pituitary signals the adrenal cortex to work harder. Increased stimulation causes gland enlargement and raises androgen output.
Why CAH can become life threatening without timely recognition
Low cortisol and, in some cases, low aldosterone reduce the body’s salt and fluid control.
Infants who are not diagnosed can develop severe dehydration, salt-wasting and shock. That is why early testing and prompt treatment are crucial.
“Early recognition and treatment turn a medical emergency into a manageable condition.”
Signs vary: some present in the first days of life, others in childhood or adolescence. With correct therapy and monitoring, most people live well—so early assessment matters.
How the adrenal glands and hormones are affected in CAH
The adrenal glands sit above the kidneys and form part of the endocrine system. These small glands release chemical messengers — hormones — that regulate energy, growth, circulation and salt balance.
The cortex versus the medulla
The gland has two parts. The medulla makes adrenaline and is not usually affected. The cortex produces cortisol, aldosterone and androgens, and is the part usually involved in CAH.
Cortisol: stress, sugar and circulation
Cortisol helps the body cope with illness and stress, keeps blood sugar steady and supports blood pressure. Low cortisol can cause weakness, low sugar and poor circulation — risks that need prompt treatment.
Aldosterone: salt, water and pressure
Aldosterone controls how the body keeps salt and water and balances electrolytes. Low levels lead to dehydration and low sodium, which can cause vomiting and collapse in infants.
Androgens and physical characteristics
Androgens are made in both sexes. When levels rise, they can cause early pubic hair, acne, rapid growth and, in girls, unusual genital appearance or virilisation.
“Shifts in hormone levels determine the signs families see — from feeding problems and vomiting to rapid growth or atypical genital appearance.”
- Gland location and role in the endocrine system
- Difference between cortex (affected) and medulla (usually spared)
- How cortisol and aldosterone shortages cause clinical risk
Causes and genetics behind CAH
At the heart of the condition are gene changes that reduce specific enzyme activity in steroid production.
How inheritance works and what “carrier” means
Most forms follow an autosomal recessive pattern. That means both parents usually carry one altered gene but remain well.
Each pregnancy has a 25% chance the child will be affected and a 75% chance they will not. Each pregnancy is an independent chance.
Enzyme defects and why 21-hydroxylase is common
CAH is an enzyme-related problem: an enzyme deficiency blocks normal cortisol—and sometimes aldosterone—synthesis.
The majority of UK cases result from 21-hydroxylase deficiency. Many resources use the term cah to mean this type because it is most frequent.
CYP21A2 changes and variable severity
Changes in the CYP21A2 gene drive 21-hydroxylase forms. Different variants produce a spectrum from mild to severe deficiency.
Both boys and girls are affected equally, though signs and timing differ between the sexes and between people.
- Incidence in the UK is roughly 1 in 10,000–1 in 18,000 births — actual cases vary by population.
- Families often benefit from genetic counselling when planning pregnancies.
“Genetic testing and counselling give families clear recurrence risks and options.”
Forms and types of Congenital adrenal hyperplasia
Different clinical forms are defined by when signs start, how severe they are and which enzyme is affected. This practical grouping helps decide urgent testing and referral.
Classic versus nonclassic (late‑onset)
Classic form cah usually appears in infancy or early childhood. It often causes clear hormone imbalances and, in some babies, life‑threatening salt loss.
Nonclassic or late‑onset forms present later. Signs are milder and may include early pubic hair, acne or irregular periods rather than an emergency.
Salt‑wasting: why low aldosterone is urgent
Salt‑wasting is a critical type where low aldosterone causes rapid salt loss, dehydration and electrolyte disturbance.
This can lead to hypovolaemia and shock in early life. Immediate assessment and fluids are essential when a baby is vomiting, lethargic or not feeding.
Simple‑virilising and overlap
Simple‑virilising form causes androgen excess with less marked salt loss. Virilisation and rapid growth are common signs.
Presentations overlap: some children show features of both salt‑wasting and simple‑virilising, so clinicians treat the child, not just the label.
Rarer enzyme types
Less common disorders involve other enzyme blocks and produce different hormone levels. Each type calls for tailored testing to confirm the exact pattern.
“Recognising the likely form by age of onset and red flags speeds referral and life‑saving treatment.”
- Practical point: infants with poor feeding, vomiting or collapse need urgent review for possible salt‑wasting.
- Later signs: early puberty, acne or irregular periods suggest nonclassic forms and outpatient assessment.
Symptoms and signs across infancy, childhood and puberty
Symptoms range from urgent metabolic collapse in newborns to gradual hormone effects in adolescence. Recognising age‑specific signs helps speed assessment and treatment.
Newborn warning signs
Urgent signs that need immediate NHS review include:
- vomiting, poor feeding and dehydration
- lethargy or reduced consciousness
- low blood sugar and electrolyte imbalance
Salt‑wasting crisis features
A salt‑wasting crisis shows falling sodium, worsening dehydration and a risk of collapse or shock. This is an emergency requiring fluids, electrolyte correction and clinician‑led testing.
Ambiguous genitalia in females
Ambiguous genitalia at birth can indicate a classic form and needs prompt specialist assessment. Sensitive communication with parents and urgent endocrine review are essential.
How boys may present
Boys often have typical genitalia at birth. Early clues may be repeated vomiting, poor weight gain, dehydration or rhythm changes, so clinicians should consider hormone causes.
Childhood and puberty changes
Children may show rapid growth, early pubic hair or early puberty from excess androgens. Early height gain can be misleading because bone age advances and final adult height may fall without treatment.
Adolescent signs
Teenagers can develop acne, facial hair, a deeper voice and menstrual irregularities in females. These features reflect ongoing androgen excess and need specialist review.
“Seek NHS assessment for red flags; avoid self‑diagnosis and follow clinician‑led testing.”
How CAH is diagnosed in the UK clinical pathway
When a baby has unusual genitalia or a child shows unexplained vomiting, clinicians begin a focused diagnostic pathway. Early recognition directs urgent care and helps plan appropriate treatment and follow-up.
Initial clinical assessment
Triggers for referral include atypical genitalia at birth, repeated vomiting or dehydration, failure to thrive, early puberty signs, or signs of androgen excess in later childhood.
Clinicians assess hydration, blood pressure, skin pigmentation and growth charts. Careful history seeks feeding, vomiting and family gene information. Specialist endocrine input is arranged quickly when crisis is possible.
Blood and urine testing
Blood and urine samples check sodium, potassium, glucose and key hormone levels. These tests guide immediate replacement planning and monitor severity of the salt‑wasting risk.
17‑hydroxyprogesterone is a principal marker used to screen for 21‑hydroxylase deficiency. Markedly raised levels point to this common form and speed confirmatory testing and treatment decisions.
Imaging, bone age and genetic confirmation
X‑rays for bone age help assess growth advancement and guide long‑term treatment for childhood and adolescent care.
Genetic testing identifies the exact gene change and confirms the diagnosis for those cases where biochemical tests are unclear. Genetic counselling then explains recurrence risk and family planning options.
| Step | Purpose | Typical findings |
|---|---|---|
| Clinical exam | Identify red flags and hydration status | Atypical genitalia, low urine output, low BP |
| Blood/urine tests | Measure electrolytes and hormone levels | Low sodium, high potassium, abnormal glucose |
| 17‑OHP measurement | Screen for 21‑hydroxylase deficiency | Raised 17‑hydroxyprogesterone |
| Imaging & bone age | Assess growth and pubertal advancement | Advanced bone age if androgen excess present |
| Genetic testing & counselling | Confirm type, inform recurrence risk | Identified gene variant and family advice |
Treatment and long-term management
Immediate stabilisation aims to prevent shock. Intravenous fluids restore blood volume and correct sodium and potassium. Rapid correction protects the brain, heart and kidneys.
Hormone replacement is lifelong for most affected children. Daily cortisol replacement is central. Aldosterone is added when salt‑wasting is present to keep electrolytes stable.
Practical sick‑day rules
During fever, vomiting, surgery or injury the usual dose of steroid must increase. These stress doses mimic the normal rise in cortisol and prevent life‑threatening decline.
Monitoring and dose adjustment
Clinicians use regular blood tests and growth checks to fine‑tune doses. Adjustments are frequent in infancy, childhood and puberty as needs change.
Managing androgen excess and puberty
Treatment balances lowering excess androgens while avoiding overtreatment that can slow growth. Additional hormone therapy may delay early puberty and protect final height.
Multidisciplinary support and fertility
Care is usually shared between paediatric endocrinology, urology and specialist nurses. Psychological support helps families with sensitive decisions.
Some females have reduced fertility. With specialist endocrine and obstetric oversight, many carry pregnancies to term; delivery planning may include caesarean and close steroid management.
“With timely stabilisation, regular monitoring and clear sick‑day guidance, most children and adults lead full lives.”
| Care phase | Key actions | Why it matters |
|---|---|---|
| Acute stabilisation | IV fluids, electrolyte correction, urgent bloods | Prevents shock and organ injury |
| Maintenance therapy | Daily cortisol ± aldosterone, routine tests | Keeps salt and sugar steady and controls androgens |
| Surgery/pregnancy | Stress dosing, MDT planning, obstetric review | Reduces crisis risk and supports safe delivery |
Conclusion
In short, CAH is a lifelong but treatable condition caused by an enzyme fault that alters cortisol — and sometimes aldosterone — production, leading to adrenal hyperplasia and hormone imbalance.
Early recognition matters. Missed salt‑wasting can be life threatening, so urgent assessment for newborns with vomiting, poor feeding or collapse is essential.
The core points remain: what the condition is, how glands and hormones are affected, why genetics guide risk, and how forms range from classic to nonclassic.
Diagnosis in the UK uses targeted blood and urine tests (including 17‑OHP where relevant), imaging and genetic counselling. Management blends acute stabilisation, daily hormone replacement, clear sick‑day rules and regular monitoring to protect growth, puberty and wellbeing.
Use this information to support informed conversations with NHS clinicians if there is family history or worrying symptoms.
