Clinical Guidance

Fibrous dysplasia/ McCune-Albright syndrome (FD/MAS) results from mosaic somatic activating pathogenic variants in GNAS, which encodes the cAMP pathway-associated G protein Gs (Gs alpha subunit). Affected tissues can include those derived from ectoderm, mesoderm, and endoderm, and commonly include skin, skeleton, and certain endocrine organs. However, because Gs signaling is present in virtually every tissue, additional sites may be affected. The phenotypic spectrum of FD/MAS ranges from asymptomatic incidental findings to neonatal lethality. There is a high degree of variability between individuals, both in the number of affected tissues and the degree to which they are affected.

Diagnostic Criteria

Fibrous dysplasia/ McCune-Albright syndrome (FD/MAS) is usually diagnosed based on characteristic clinical, radiographic, and laboratory manifestations, although formal diagnostic criteria have not been published.

Suggestive Findings

FD/MAS should be suspected in individuals with any of the following skin, skeletal, or endocrine features. Skin. Individuals may have characteristic hyperpigmented skin macules. These have been referred to as caf au lait macules; however, this does not accurately reflect their appearance on darker-skinned individuals.

Management Guidelines

Evaluations Following Initial Diagnosis

After the initial diagnosis, all individuals with fibrous dysplasia/ McCune-Albright syndrome (FD/MAS) should be evaluated to determine the extent of disease. The presence of any features of FD/MAS should prompt more detailed clinical evaluation for additional manifestations. The authors recommend the following studies, if they have not already been completed.

Surveillance Guidelines

Due to the mosaic nature of FD/MAS, the clinical findings in affected individuals can vary significantly, with some individuals having involvement of only one organ system and others having more widespread involvement. Additionally, some features are age dependent and are either not likely to develop after a certain age or are more likely to affect older individuals. The following information on surveillance applies to individuals who have already been evaluated for signs and symptoms of the condition and in whom the extent of disease has been assessed; surveillance will need to be tailored to the individual's age and known affected organ systems . Table 5. Fibrous Dysplasia/ McCune Albright Syndrome: Surveillance to Consider