Multigene deletions on chromosome 20q13.13-q13.2 including SALL4 result in an expanded phenotype of Okihiro syndrome plus developmental delay.

Okihiro syndrome results from truncating mutations in the SALL4 locus on the chromosome 20q13.13-q13.2. Deletions of the whole SALL4 coding region as well as single exon deletions are also a common cause of Okihiro syndrome and indicate haploinsufficiency as the disease causing mechanism. The phenotypes caused by SALL4 deletions are not different from those caused by point mutations. No multigene deletion including SALL4 has been documented to date. Here we report the detection and molecular characterization of four novel, overlapping microdeletions, all spanning SALL4 and flanking genes, in four unrelated cases with features of Okihiro syndrome and variable degrees of psychomotor delay. All deletions were first identified and mapped by quantitative Real Time PCR. Subsequently, three of four deletions were mapped in further detail by high-resolution array CGH (244k oligo-arrays). All cases had larger deletions of varying size (1.76-1.78 Mb, 2.01-2.05 Mb, 2.16-2.17 Mb, and 1.3-2.8 Mb, respectively), which included SALL4 plus 3 to 7 additional functional genes. While three cases with largely overlapping deletions are mildly developmentally delayed, the only patient with a more centromeric deletion is clearly mentally retarded. In this patient, four genes (MOCS3, DPM1, ADNP, BCAS4) are deleted, which were not affected in the other three cases, suggesting that the deletion of one or more of these genes contributes to the mental retardation. Since two of the four cases presented with choanal atresia, large deletions including SALL4 should be considered in the differential diagnosis of children with suspected CHARGE syndrome but without detectable CHD7 mutations.