Hemizygosity for the COP9 signalosome subunit gene, SGN3, in the Smith-Magenis syndrome.

Smith-Magenis syndrome (SMS) is a multiple congenital anomaly/mental retardation syndrome associated with an interstitial deletion of chromosome band 17p11.2. The critical region is extremely gene-rich and spans approximately 1.5-2.0 Mb of DNA. Here we report the localization and partial characterization of the gene for subunit 3 of the COP9 signalosome, SGN3. SGN3 maps to the distal portion of the SMS critical interval, between SREBF1 and cCI17-638. We assessed the potential effect of haploinsufficiency of SGN3 in SMS patient lymphoblastoid cell lines through transfection studies and western analysis. Our results indicate that the COP9 signalosome assembles properly in these cells and appears to have normal expression and a kinase function intact. However, because the role of the COP9 signalosome in embryogenesis or differentiation is still uncertain, we cannot rule out the involvement of this gene in the Smith-Magenis syndrome.