Although the region on chromosome 2 was not the best candidate locus (the lower LOD score and homozygous alleles of each linked marker are common in Tunisian population), we chose to investigate the CERKL gene, encoding a ceramide kinase, as candidate since it has been described to cause nonsyndromic autosomal recessive RP (RP26) [7]. The gene discussed is CERK; the disease is retinitis pigmentosa 26.