Weight Loss with McCune-Albright Syndrome in South Africa

McCune-Albright Syndrome (MAS) is a rare, non-inherited mosaic genetic disorder caused by a somatic mutation in the GNAS gene — a change that occurs early in embryonic development, affecting a subset of cells throughout the body. The classic triad consists of polyostotic fibrous dysplasia (weakened, deformed bones), café-au-lait skin patches with irregular "coast of Maine" borders, and precocious puberty. But MAS is far more than these three features: it can cause multiple simultaneous endocrine gland overactivations, including hyperthyroidism, Cushing's syndrome, acromegaly, and hyperparathyroidism — each of which affects body weight and composition in different ways. For South Africans living with MAS, weight management is a complex, multi-variable challenge that requires specialist coordination rather than a one-size-fits-all approach.

Understanding McCune-Albright Syndrome

The GNAS gene encodes the alpha subunit of a G-protein (Gsα) that transmits hormonal signals into cells. The activating mutation in MAS causes this signalling protein to be permanently "switched on" in affected cell populations — essentially making those cells behave as if they are continuously receiving a hormonal stimulation signal. Depending on which tissues carry the mutation and in what proportion, different features dominate.

Core features of MAS:

• Polyostotic fibrous dysplasia (PFD): Normal bone tissue is replaced by fibrous tissue, causing weakened, deformed bones that fracture easily. The femur (thigh bone) is most commonly affected, often causing a "shepherd's crook" deformity and a limp. Craniofacial involvement can affect vision and hearing. Bone pain and pathological fractures are common.
• Cafe-au-lait macules: Large, flat, irregular skin patches with characteristic jagged borders. Typically unilateral and following lines of Blaschko.
• Precocious puberty: Most common in girls — early breast development and vaginal bleeding before age 8, driven by autonomous ovarian cysts producing oestrogen independent of the normal pituitary-gonadal axis.

Endocrine overactivation syndromes in MAS:

• Hyperthyroidism: Autonomous thyroid nodules or diffuse goitre. Causes weight loss, but also muscle wasting, fatigue, and cardiac arrhythmia — weight loss in this context is harmful.
• Cushing's syndrome: Autonomous cortisol excess from adrenal nodules. Causes classic central obesity, thin limbs, moon face, buffalo hump, stretch marks, hypertension, and diabetes. Typically presents in infancy and may remit spontaneously.
• Acromegaly / gigantism: Autonomous growth hormone (GH) excess from pituitary adenoma. Causes soft tissue overgrowth, insulin resistance, coarsened features, enlarged hands and feet. GH excess promotes weight gain via insulin resistance.
• Hyperparathyroidism: Excess PTH from parathyroid gland involvement. Causes hypercalcaemia, kidney stones, bone disease, fatigue.
• Hypophosphataemia: Elevated FGF-23 from fibrous dysplasia lesions causes renal phosphate wasting — bone pain, muscle weakness, and fracture risk are worsened.

No two MAS patients are identical. The combination and severity of features depend entirely on which tissues are affected and to what degree. Prevalence is estimated at 1 in 100,000 to 1 in 1,000,000 — it is genuinely rare.

How MAS Affects Weight and Body Composition

The weight implications of MAS depend entirely on which endocrine glands are overactive:

• If Cushing's syndrome is active: Central obesity, muscle wasting in limbs, metabolic syndrome, hypertension, diabetes. Weight loss is desirable but cortisol excess makes it extremely difficult — the body resists fat mobilisation from central depots.
• If hyperthyroidism is active: Unintentional weight loss, muscle catabolism, heat intolerance. Weight gain may actually be a goal while treating the thyroid.
• If acromegaly / GH excess is present: Insulin resistance promotes fat accumulation, particularly visceral fat. Soft tissue overgrowth adds mass but is not adipose tissue. Weight management here is primarily about metabolic risk reduction.
• If multiple endocrine glands are involved simultaneously: Competing effects can mask each other, making weight trends difficult to interpret without biochemical monitoring.
• If fibrous dysplasia is severe: Pain, limp, fracture risk, and potential wheelchair use dramatically reduce physical activity — a major driver of weight gain in MAS even without active endocrinopathy.

Dietary Principles for MAS in South Africa

Because MAS presentations vary so widely, dietary guidance must be tailored to the dominant active condition. These are general principles applicable across most MAS presentations:

Anti-inflammatory Mediterranean-style base diet:

• Olive oil, avocado, and fatty fish (sardines, mackerel, salmon) for anti-inflammatory omega-3 fats
• Abundant vegetables: morogo, spinach, broccoli, butternut, cabbage, tomatoes
• Legumes for protein: lentils, chickpeas, sugar beans — affordable, high-fibre, low-GI
• Whole grains: brown rice, oats, whole-wheat bread, samp
• Lean protein: chicken breast, eggs, tinned pilchards
• Rooibos tea: anti-inflammatory polyphenols, naturally caffeine-free, calorie-free — a South African staple that fits perfectly in any anti-inflammatory eating plan

For Cushing's syndrome (active or treated):

• Low sodium: Cortisol promotes sodium retention and hypertension. Severely restrict biltong, boerewors, packet soups, Aromat, and processed meats. Target under 1,500 mg sodium/day.
• Low glycaemic index: Cortisol excess drives insulin resistance and diabetes. Avoid refined carbohydrates entirely — white bread, white rice, sugary drinks, biscuits.
• Adequate calcium and vitamin D: Cortisol accelerates bone loss. Fortified low-fat milk, yoghurt, tinned fish with bones (sardines), and 15–20 minutes of morning sunlight support bone health. MAS patients with FD already have bone vulnerability — do not compound it with nutritional deficiency.
• Potassium-rich foods: Cortisol promotes potassium loss. Include bananas, avocado, butternut, and sweet potatoes.

For acromegaly / GH excess:

• Low refined carbohydrate: GH excess worsens insulin resistance. Prioritise low-GI foods, avoid sugary foods and drinks.
• High protein: GH promotes protein anabolism; adequate dietary protein (1.5 g/kg/day) supports this and reduces muscle catabolism.
• Monitor blood glucose: GH-related diabetes can develop — test fasting glucose regularly and flag to endocrinologist.

For fibrous dysplasia with hypophosphataemia:

• Phosphate-rich foods: Dairy products, legumes, nuts, and fish support phosphate levels when FGF-23-driven losses occur.
• Avoid excessive calcium supplementation without phosphate: Can worsen imbalance. Follow endocrinologist guidance.
• Vitamin D: Active vitamin D (calcitriol) is often prescribed — dietary sources support but do not replace supplementation in hypophosphataemia.

Exercise and Physical Activity in McCune-Albright Syndrome

Exercise in MAS is complicated by the bone disease. The primary rule is: protect the affected bones.

Assessment before starting any exercise:

• Get a current bone survey (skeletal X-rays) and/or MRI of affected bones from your orthopaedic surgeon
• Identify which bones are affected by fibrous dysplasia — the femur, tibia, ribs, skull, and pelvis are common sites
• Understand your current fracture risk — bisphosphonate treatment status affects bone stability
• Cardiac clearance if hyperthyroidism or GH excess is or was present

Safe exercise options:

• Swimming and hydrotherapy: Zero impact on bones. Ideal for most MAS patients, including those with femoral or lower limb involvement. Provides cardiovascular benefit and supports muscle tone that protects weakened bones.
• Upper body resistance (if lower limb bones are affected): Seated resistance band work for arms and shoulders. Maintains upper body strength and metabolic rate without loading the femur or tibia.
• Chair-based aerobics: If walking is limited by limp or pain, seated aerobic movements can raise heart rate safely.
• Cycling (stationary bike): Lower impact than walking for femoral FD, but avoid if femoral deformity is severe (shepherd's crook) — consult physiotherapist first.
• Gentle walking on flat ground: Suitable if lower limb FD is mild and orthopaedic surgeon has cleared weight-bearing. Use appropriate orthotic footwear.
• Physiotherapy core strengthening: Core and hip muscle strength stabilises the pelvis and spine, reducing abnormal loading forces on dysplastic long bones.

Exercise to avoid:

• High-impact sports: running, jumping, contact sports, tennis, aerobics classes
• Heavy weight-bearing resistance training involving affected bones
• Any activity with fall risk (cycling outdoors, roller skating, team sports) if bone fragility is present

Medical Management Relevant to Weight

• Bisphosphonates (zoledronic acid, pamidronate): Used for fibrous dysplasia — reduce bone pain and pathological fractures. Some bisphosphonates mildly reduce physical capacity; report new fatigue to your doctor.
• Antithyroid drugs (carbimazole) or surgery: Treating hyperthyroidism typically causes weight gain as metabolism normalises — do not reduce intake to compensate; let the thyroid normalise first.
• Octreotide / lanreotide (somatostatin analogues): For GH excess — may cause glucose normalisation and modest weight reduction.
• Adrenal Cushing's treatment: Adrenalectomy (removal of overactive adrenal gland) in infantile MAS-Cushing's. Post-surgical steroid requirements must be carefully managed.
• Aromatase inhibitors (letrozole, anastrozole): For precocious puberty — no major direct weight effects but support hormonal normalisation.

Finding Specialist Care in South Africa

MAS requires multidisciplinary management. In South Africa, this typically means:

• Endocrinologist: For thyroid, adrenal, pituitary, and bone mineral metabolism management
• Orthopaedic surgeon with metabolic bone experience: For fibrous dysplasia surveillance and fracture prevention
• Paediatric endocrinologist: For precocious puberty management in girls
• Ophthalmologist: Annual eye assessment for craniofacial fibrous dysplasia affecting vision
• Audiologist: Skull base FD can compress auditory nerves
• Registered dietitian: ADSA-registered, ideally with endocrine or metabolic experience (adsa.org.za)
• Rare Diseases South Africa (RDSA): rdsa.co.za for patient support and specialist referral guidance

International resources: The Fibrous Dysplasia Foundation (fibrousdysplasia.org) and the MAS Alliance provide the most current clinical guidelines, physician directories, and patient community support.

Key Takeaways

• MAS is caused by a mosaic GNAS activating mutation that drives multiple simultaneous endocrine overactivations alongside fibrous bone disease
• Weight management goals and dietary advice depend on which endocrine glands are active — always work with an endocrinologist to know your current biochemical status
• A Mediterranean-style, low-sodium, low-GI diet works as a base for most MAS presentations
• Low-sodium eating is especially important if Cushing's features are present or treated
• Exercise must avoid impact on affected bones — swimming, hydrotherapy, and upper body resistance are the safest choices
• Protect bone health through adequate calcium, vitamin D, and phosphate alongside any bisphosphonate treatment
• MAS requires tertiary centre management — primary care alone is insufficient for this complex, multi-system condition

Disclaimer: This article is for informational purposes only and does not constitute medical advice. McCune-Albright Syndrome requires specialist management — consult your endocrinologist, orthopaedic surgeon, and registered dietitian before making any changes to your diet, exercise, or medical treatment plan.

Sources: Lumbroso S et al. (2004). Activating Gsα mutations: analysis of 113 patients with signs of McCune-Albright syndrome. JCEM 89(5). | Boyce AM et al. (2015). Fibrous dysplasia/McCune-Albright syndrome. Best Practice & Research: Clinical Endocrinology & Metabolism. | Fibrous Dysplasia Foundation: fibrousdysplasia.org.