Albright syndrome

Nature of the disease and genetic mechanisms

Albright syndrome belongs to the broad group of constitutional bone diseases, specifically dysplasias. Unlike dysostoses, which have a static phenotype due to a one-time insult during intrauterine development, dysplasias are characterized by an evolving phenotype due to continued abnormal growth of bone and cartilage tissue.

The syndrome is based on the phenomenon of somatic mosaicism. This is a rare inheritance variant in which at least two different cell lines originating from a single zygote are present in the human body. It is believed that the genetic mutation causing this disease is absolutely lethal to the embryo if present in all cells without exception. Survival is possible only thanks to mosaicism. The mixture of mutant and healthy cell pools explains why lesions are always asymmetric or strictly focal in nature. The pathology is traditionally included in the medical list of syndromes accompanied by asymmetric shortening or local tissue overgrowth (overgrowth).

Clinical presentation and classical triad

A definitive diagnosis requires the synthesis of a significant amount of clinical, biochemical, radiological, and genetic data. Classic McCune-Albright syndrome manifests as a clear triad of features:

1. Polyostotic fibrous dysplasia. As a rule, the pathological process is markedly unilateral. Most commonly affected are the proximal femur, tibia, and pelvic bones. The degree of involvement can vary significantly: from involvement of just two bones to massive dysplasia of over 75% of the entire skeleton.
2. Dermatological manifestations. Characterized by the presence of specific skin pigment spots traditionally described as café-au-lait spots. A crucial diagnostic criterion is that these spots are located ipsilaterally, i.e., strictly on the same side of the body as the bone deformations. The spots are identified in approximately 30–50% of patients with the polyostotic form of the disease.
3. Endocrine disorders. The pathology is accompanied by hyperactivity of endocrine glands, primarily pituitary hormone hypersecretion. In pediatric practice, this most commonly debuts as precocious puberty in girls. Pituitary hypersecretion also provokes the development of Cushing's syndrome and a number of other endocrinopathies.

Morphology of the skeletal system lesions

The bone component of the disease is represented by fibrous dysplasia (Fibrous Dysplasia, FD). This is a specific developmental anomaly characterized by a systemic defect in osteoblast differentiation and maturation. As a consequence, normal bone marrow tissue is gradually crowded out and replaced by pathological fibro-osseous tissue (fibro-osseous tissue).

Isolated fibrous dysplasia in itself is a fairly common pathology, accounting for about 7% of all known benign bone tumors. Three-quarters of all cases are diagnosed in individuals under 30 years of age, with no marked gender predilection.

The insidious nature of the disease lies in the fact that it proceeds completely painlessly and asymptomatically. The silent period continues until the cortical layer thins, ultimately leading to local bone curvature or the occurrence of spontaneous pathological fractures.

Imaging features

Accurate and timely imaging diagnosis is critically important: a definitive diagnosis allows physicians to anticipate complications, prescribe specific treatment, and provide accurate genetic counseling.

On radiographs and CT scans, a typical lesion appears as an area of local bone expansion and widening (bony expansion) with a characteristic ground-glass pattern (ground-glass appearance). In some cases, the structure of dysplastic foci may be mixed: predominantly lytic, sclerotic, or representing a combination of all three tissue remodeling variants.

The severity of clinical manifestations directly depends on the localization of pathological fibro-osseous masses. Involvement of the facial skeleton and skull bones is particularly dangerous. The proliferation of abnormal tissue leads to mechanical narrowing of the natural openings of the skull base, which is fraught with severe cranial nerve entrapment. For example, involvement of the orbital walls leads to narrowing of the optic canal (optic foraminal narrowing), accompanied by clinically pronounced exophthalmos.

Class and exam questions

What else to study on this topic

• Cherubism: hereditary fibrous dysplasia of the jaws
• Constitutional bone diseases: differences between dysplasias and dysostoses
• Genetic syndromes accompanied by asymmetric tissue overgrowth
• Molecular mechanisms of genomic imprinting and uniparental disomy
• Simple and aneurysmal bone cysts: imaging differential diagnosis

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.