• Cytogenetics

We read with interest the article by Rivera-Brugués et al1 in a recent issue of this journal describing 3 patients out of 1523 patients with unexplained mental retardation. Analysis by whole genome array-CGH (comparative genomic hybridisation) showed an intragenic heterozygous deletion in the VPS13B gene, and the subsequent sequencing of the VPS13B gene revealed by one-point mutation in the second allele in all three patients.

In a previous study, we screened the VPS13B gene in 34 patients (28 families) with a suspicion of Cohen syndrome and identified 14 different mutations in 8 families (12 patients).² The mutations were found in a compound heterozygous state in five families and in a homozygous state in one consanguineous family. In two other families (patients P1-F1, P2-F2 and P3-F2), only one heterozygous mutation was found (25% of families). Since the previous publication, 20 additional patients were screened, leading to the identification of compound heterozygosity in one patient and only one mutational event in four patients from three different families. All the patients with one or two mutational events in VPS13B were considered as having Cohen syndrome according to both Chandler's and Kolehmainen's criteria.3 4 Since the 244K array-CGH Agilent comprises 102 probes within the VPS13B gene (figure 1), we sought to identify a large intragenic event in two groups: group 1 included the five families in which one mutational event …