A person is diagnosed with MAS if he or she has a combination of any of the following symptoms1:
- Café-au-lait (French for "coffee with milk") spots, which are light brown birthmarks
- Polyostotic fibrous dysplasia (PFD), which is a bone irregularity
- Precocious puberty, which is premature development in a child
- Hyperthyroidism, which is an overactive thyroid gland
- Growth hormone excess
- Cushing syndrome, an overactivity of the adrenal glands
- Sertoli cell hyperplasia and Leydig cell hyperplasia, which are tumors in the testicles
Read more about the symptoms of MAS.
A healthcare provider may use X-rays to examine bones for PFD. He or she may perform ultrasounds to look for an abnormal appearance of the thyroid or testicles. Blood tests may be done to check for abnormal hormone levels. He or she may take a small sample or biopsy of abnormal bone tissue and analyze it to confirm PFD, thereby confirming MAS.2
A genetic test is also available to detect the GNAS gene mutation, but it is often not reliable for diagnosing MAS. The diagnosis of MAS is made clinically, based on the presence of characteristic features.3 Learn more about MAS and genetic testing.
Symptoms and severity of MAS vary, so diagnosis may occur at birth or later in childhood.4