Synonyms

• MAS
• polyostotic Fibrous dysplasia with precocious puberty

Category

Syndrome

Behaviour

Benign

Gender

Female

Tissue of Origin

Bone

Epidemiology

• Somatic GNAS mutations (post-zygotic)
• Sporadic presentation (not inherited)
• Affects 1 in 25,000 live births
• Female predominance in presentation
• Highly Variable phenotype

Clinical Features

• Cafe-au-lait spots (characteristic coast of Maine pattern)
• Precocious puberty (especially girls)
• Polyostotic Fibrous dysplasia
• Endocrinopathies: hyperthyroidism, hyperparathyroidism
• Growth hormone excess
• Cardiac arrhythmias possible

Location

• Femur and pelvis most common
• Polyostotic: multiple Bones affected
• Often asymmetric distribution

Imaging

• Skeletal survey: Fibrous dysplasia distribution
• Hormonal imaging: pituitary MRI, thyroid ultrasound
• Cardiac evaluation if indicated

Pathology

• Fibrous dysplasia on biopsy
• Benign fibroblastic tissue with immature woven Bone

Genetics

• GNAS somatic mutations (post-zygotic)
• Different from germline GNAS (pseudohypoparathyroidism)
• Variable tissue involvement by mutation timing

Treatment

• Observation of stable Fibrous dysplasia
• Bisphosphonates for symptomatic Bone disease
• Endocrinology management: GnRH agonists for precocious puberty
• Surgical correction if severe deformity

Prognosis

• Benign Fibrous dysplasia
• Malignant transformation rare (0.5%)
• Prognosis depends on endocrine complications

Key Points

• SYSTEMIC GENETIC Syndrome
• GNAS somatic mutations
• Cafe-au-lait spots + precocious puberty classic
• Polyostotic Fibrous dysplasia characteristic
• Malignancy risk Low but present

Workup - Blood Tests

• Hormone screening: LH, FSH, testosterone/estradiol (precocious puberty)
• TSH, free T4 (hyperthyroidism)
• Calcium, phosphate, PTH (hyperparathyroidism)
• Growth hormone (gigantism)

Workup - Local Imaging

• Skeletal survey: assess FD extent
• Pelvic imaging: screen for ovarian cysts (source of precocity)
• MRI brain: pituitary assessment if GH excess
• Thyroid ultrasound

Workup - Biopsy

• Not required for diagnosis
• If Fibrous dysplasia uncertain on imaging

Workup - Staging

• Baseline imaging: whole skeleton
• Hormonal assessment: comprehensive screen

Workup - Other

• Endocrinology consultation
• Genetics counselling
• Ophthalmology: screen for vision problems
• Cardiac evaluation if arrhythmias

Follow-up Summary

• Regular endocrinology Follow-up: hormone monitoring
• Annual skeletal imaging if progressive symptoms
• Monitor for Malignant transformation
• Screen for additional endocrine complications