Editor—Microdeletions in 22q11.2 are associated in 80-90% of cases with DiGeorge syndrome (DGS, MIM 188400) or velocardiofacial syndrome (VCFS, MIM 192430) and occur with an estimated frequency of 1/4000 live births.1 Most deletions are the result of a de novo event, although probably 6-28% of them are familial.2 The phenotype of the patients is mainly characterised by conotruncal heart defect, cleft palate, immune deficiency, neonatal hypocalcaemia, and facial dysmorphism. The number of clinical symptoms varies substantially and their reduced expression can lead to a mild phenotype.3 There does not seem to be a correlation between the presence or the size of a microdeletion and the clinical manifestation of the syndrome. Molecular analyses have shown that most patients have a deletion of about 1.5 or 3 Mb.4 5 The length of the delineated minimal critical region for a DGS/VCFS phenotype, however, is only 480 kb.6 Reports of patients with a DGS/VCFS-like phenotype having a deletion in 10p7 led to the definition of a second critical region, DGSII. However, the incidence of 10p deletions is low in comparison to the rate of microdeletions in 22q.8 9 The high rate of sporadic microdeletions in 22q11.2 provides evidence for frequent meiotic rearrangements as a molecular basis for the development of this structural aberration.

In order to ascertain such rearrangements in patients with a 22q11.2 deletion, we performed haplotype analyses on five patients and their unaffected relatives using 11 polymorphic STRP markers from the DGS/VCFS critical region …