6 June 2011
We read with interest the article by Kannu et al.1 and agree that COL2A1 mutations demonstrate significant phenotypic variability, a key feature that contributes to the under-recognition and under-diagnosis of the associated type II collagenopathies. We would suggest, however, a cautionary note to the recommendation that a complete skeletal survey is essential for the clinical diagnosis of most type II collagenopathies.
A fundamental clinical hallmark of type II collagenopathies is a congenital abnormality in vitreous embryological development which then manifests as an abnormal architecture visible on slit-lamp examination. Illustrations of this have been published recently.2
We would respectfully suggest, therefore, that before moving to radiological investigation suspected individuals (and their siblings) should first be examined for abnormalities in their vitreous phenotype. This is a relatively simple procedure and has 3 potentially very important advantages. Firstly it will assist in clinical diagnosis, which may then avoid the need to expose individual patient to radiation purely for purposes of clinical diagnosis. Secondly it will assist greatly in the identification of the emerging array of ocular-only variants of type II collagenopathies3,4 who have a high risk of blindness through retinal detachment, but which would be overlooked or excluded using diagnostic criteria constrained by the requirement for a radiological diagnosis.5,6
Thirdly, in addition to being a diagnostic hallmark, vitreous assessment can been used to guide molecular genetic analysis in a more efficient manner than blind screening of all candidate genes.2,7