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Editor,—We read in a recent issue of the journal the paper by Trainer et al on 22q11 microdeletion (del22q11) in patients with tetralogy of Fallot.1 Del22q11 was detected in patients with classic and mild DiGeorge/velocardiofacial syndrome, but also in ‘non-dysmorphic’ patients. The authors suggest that fluorescence in situ hybridisation (FISH) for del22q11 should routinely be performed in all patients with tetralogy of Fallot. Our experience on a large sample of patients with isolated conotruncal heart defects (CTHDs) demonstrated, on the contrary, that clinical examination can select the patients at risk for del22q11.2 3 From 1993 to 1996 we evaluated 315 children with CTHD (table 1). All patients underwent phenotypical evaluation. Particular attention was paid to minor dysmorphic features associated with DiGeorge/velocardiofacial syndrome,4 including lateral displacement of inner canthi, narrow upslanting palpebral fissures, prominent nose with hypoplastic nares, small mouth, dysmorphic ears, and slender fingers. Standard karyotype on peripheral lymphocytes was performed, and FISH was used for detecting del22q11 in all cases.5 Patients presenting with CTHD that was associated with one or more extracardiac anomalies were considered as syndromic. The distribution of syndromic and isolated cases in the different types of CTHD and the presence of del22q11 is shown in table1. Only one of the children with isolated CTHD presented del22q11. Five patients originally diagnosed as isolated were subsequently included in the group of syndromic cases, because of the presence of subtle facial dysmorphisms which was previously overlooked.
The occurrence of del22q11 in our series of true isolated CTHDs is extremely low. In order to define the exact prevalence of del22q11 in non-syndromic CTHDs it is essential to exclude patients with subtle dysmorphisms evoking features of DiGeorge or velocardiofacial syndromes.1 6 These dysmorphisms may be barely recognisable, but their presence can be associated with a high prevalence of del22q11.1 A precise phenotypical analysis and clinical follow up are essential to distinguish syndromic from isolated CTHD. We believe that accurate clinical evaluation is generally sufficient for a first screening to identify patients at risk for del22q11, and only syndromic cases should be screened for this chromosomal anomaly. Routine FISH analysis in both syndromic and isolated cases is valuable as a research tool to evaluate the exact prevalence of del22q11 in isolated CTHD and in patients with different types of cardiac malformation, but we feel that in clinical practice this technique could be reserved for patients previously selected by clinical evaluation.Letters to Editor