Background. The 22q11.2 deletion syndrome (22qDS) has more than 180 associated phenotypic features, yet genotype-phenotype correlation remains obscure. Since many of the clinical characteristics are serious, yet treatable (including congenital heart disease), clinicians must maintain a high index of clinical suspicion to recognise a suite of co-occurring phenotypic features that suggest a diagnosis of 22qDS. Óskarsdottir’s scoring schedule (the ‘O score’) is generally used to suggest the need for confirmatory fluorescent in situ hybridisation (FISH) testing, using the TUPLE 1 probe. An O score of two or more indicates the need for FISH testing. Objectives. A previous audit of FISH-positive results of patients with congenital heart disease at Red Cross War Memorial Children’s Hospital (RCWMCH) revealed a clinical recognition rate of 1.7%. However, we were concerned that the syndrome may be under-recognised in our setting. Our aims were therefore to assess the predictive value of ‘O scoring’ and to accurately determine the prevalence of 22qDS in our patient population. Methods. A prospective trial of FISH testing every new patient with congenital heart disease presenting to RCWMCH was undertaken to accurately determine the prevalence of 22qDS. The results were then compared with the ability of the O score to indicate the need for FISH testing. Results. Testing of 125 patients detected deletions in six (4.8%, 2.8 times the previously determined clinical detection rate), thereby vindicating our concern that 22qDS is under-diagnosed. Of these 125 patients, 37 had an O score of 2 or 3, yet only 6 were FISH-positive, giving the O score a positive predictive value of only 14%. Conclusion. Until a more robust alternative recognition tool is available, South African clinicians should use all clinical recognition criteria liberally to suggest the need for formal testing for 22qDS.
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