What is Gardner syndrome?

What is Gardner Syndrome

Gardner syndrome is a variant of familial adenomatous polyposis (FAP) characterized by the combination of multiple colorectal adenomas with extracolonic manifestations including osteomas (particularly in the skull and facial bones), dental abnormalities, soft tissue tumors (epidermoid cysts, fibromas, desmoid tumors), and congenital hypertrophy of the retinal pigment epithelium 1.

Genetic Basis and Inheritance

Gardner syndrome is an autosomal dominant disorder caused by mutations in the APC gene, the same gene responsible for FAP 1. Between 20-30% of cases arise de novo without family history 2, 3. The syndrome has high penetrance with variable expression, meaning affected individuals will almost certainly develop manifestations, though the severity varies 2.

Clinical Manifestations

Colorectal Features

• Multiple adenomatous polyps throughout the colon and rectum (typically >100 in classic FAP, though Gardner syndrome can present with fewer)
• Virtually 100% risk of colorectal cancer by age 40-50 if the colon remains in place 1, 3
• Gastric and duodenal polyps are common 1

Extracolonic Manifestations (Key Diagnostic Clues)

The extracolonic features frequently appear before gastrointestinal symptoms, making early recognition critical 2, 3:

• Osteomas: Multiple benign bone tumors, particularly affecting the skull, mandible, and maxilla 1, 4, 5
• Dental abnormalities: Supernumerary teeth, odontomas, impacted teeth 1
• Soft tissue tumors:
  • Epidermoid cysts (characteristic finding) 1, 6
  • Fibromas and fibromatosis (can mimic breast malignancy) 7
  • Desmoid tumors 1
• Congenital hypertrophy of retinal pigment epithelium 1, 2
• Other tumors: Thyroid carcinoma (particularly papillary type), brain tumors, adrenal adenomas 1, 4, 7

Diagnostic Approach

Diagnosis requires identifying both the intestinal polyposis and characteristic extracolonic manifestations 1. The syndrome may first be suspected when patients present with craniofacial osteomas or other extraintestinal features 4, 2.

Key Diagnostic Steps:

1. Colonoscopy to identify multiple adenomatous polyps
2. Genetic testing for APC mutations (detects mutations in 80% with >1000 adenomas, 56% with 100-999 adenomas) 1
3. Systematic evaluation for extracolonic manifestations:
   • CT scan of skull/facial bones for osteomas
   • Ophthalmologic examination for retinal changes
   • Thyroid evaluation
   • Skin examination for epidermoid cysts

Clinical Significance and Pitfalls

The most critical aspect is that extraintestinal manifestations often precede gastrointestinal symptoms by years, making dentists and other specialists crucial for early diagnosis 2, 3. A patient presenting with multiple facial osteomas or epidermoid cysts should trigger investigation for Gardner syndrome 4.

Common pitfall: Soft tissue tumors, particularly fibromatosis, can mimic malignancy on imaging (appearing as irregular spiculated masses), leading to misdiagnosis 7. Histopathological confirmation is essential.

Life-saving implication: Early diagnosis allows for prophylactic colectomy before malignant transformation occurs, as untreated patients have essentially 100% risk of developing colorectal cancer 3.