What is Blau Syndrome
Blau syndrome is a rare pediatric autoinflammatory disorder caused by gain-of-function mutations in the NOD2 gene, characterized by the classic triad of granulomatous dermatitis, arthritis, and uveitis, with potential for severe complications including blindness and joint destruction if untreated 1, 2.
Genetic Basis and Pathophysiology
Blau syndrome results from autosomal dominant mutations in NOD2 (nucleotide-binding oligomerization domain 2), a pattern recognition receptor that regulates inflammatory cytokine production 3. These gain-of-function variants cause upregulation of inflammatory cytokines and resultant autoinflammation 3. The condition is considered the early-onset, monogenic form of sarcoidosis 4.
An important caveat: de novo mutations are common, and germline mosaicism in asymptomatic parents has been documented, meaning negative parental testing does not exclude the diagnosis 4.
Clinical Presentation
The disease follows a characteristic temporal pattern:
- Skin and joint manifestations typically emerge by age 2 years 2
- Ocular involvement appears around age 4 years 2
- The classic triad includes:
- Granulomatous polyarthritis (often with boggy joint swelling)
- Granulomatous dermatitis (pink papules on trunk and extremities)
- Granulomatous uveitis/iridocyclitis
Critical pitfall: Not all patients present with the complete triad simultaneously. Cutaneous manifestations may be delayed 3, and the disease is frequently misdiagnosed as juvenile idiopathic arthritis in early stages 3.
Systemic Complications
Beyond the classic triad, Blau syndrome can cause disseminated granulomatous inflammation affecting:
- Liver and kidneys 5
- Lungs
- Salivary glands
- Intestine
- Lymph nodes
- Central nervous system (rare but documented) 4
Without treatment, the disease progresses to:
- Severe joint contractures and wheelchair dependence 4
- Vision loss or complete blindness 4
- Glaucoma requiring surgical intervention 4
Diagnosis
When granulomatous disease (rash, uveitis, or arthritis) is apparent, mutational analysis of NOD2 should be considered for Blau syndrome 1.
Histopathology shows noncaseating, well-formed granulomas with relatively sparse lymphocytic inflammation and Langerhans-type giant cells 3. The diagnosis is confirmed by identifying pathogenic NOD2 variants, commonly including p.Arg334Trp and p.Arg334Gln mutations 4, 5.
Consider Blau syndrome in all children with early-onset arthritis (especially with boggy swelling) and granulomatous uveitis 5.
Prognosis
Blau syndrome should be considered a poor prognostic factor for uveitis, as it tends to be refractory to standard treatments 6. Early biologic intervention, particularly with anti-TNF-α therapies, can prevent severe complications like joint destruction and blindness 2.