Among these deleted genes are the gene for Nance-Horan syndrome and the cyclin-dependent kinase-like 5 gene (CDKL5), responsible for the early seizure variant of Rett syndrome.
Direct sequencing or SSCP analysis of the coding exons of five genes (SCML1, SCML2, STK9, RS1 and PPEF1), considered as candidate genes on the basis of their location in the critical interval, failed to detect any mutation in 12 unrelated NHS patients, thus making it highly unlikely that these genes are implicated in NHS.