A suspected genetic form of bilateral osteochondritis dissecans of the knee in a Dutch family

• A few cases of familial osteochondritis dissecans (OCD) of the knee have been reported.
• This case does not fit the presentation of the identified genes for familial OCD.
• No syndromes related to OCD could be identified.
• This case is suggestive of an unknown genetic anomaly.

Osteochondritis dissecans (OCD) mostly has an idiopathic origin, but syndromic and familial forms have been reported. Mutations of the aggrecan (ACAN) and COL9A2 genes are associated with familial OCD, but these patients present with syndromic features. This article describes a mother and a daughter who both have bilateral OCD of the medial femoral condyles, and the monozygotic twin sister of the mother who has confirmed unilateral OCD (and possible bilateral OCD) of the medial femoral condyle. No short stature or any other syndromic features were present. None of the syndromic features associated with ACAN or COL9A2 mutations or any other known syndromes were present in this case. This case suggests a possible unknown genetic anomaly.Level of evidence: IV case report.