S. Colella et al., Identical mutations in the CSB gene associated with either Cockayne syndrome or the DeSanctis-Cacchione variant of xeroderma pigmentosum, HUM MOL GEN, 9(8), 2000, pp. 1171-1175
Xeroderma pigmentosum (XP) and Cockayne syndrome (CS) are two hereditary di
sorders in which photosensitivity is associated with distinct clinical and
cellular phenotypes and results from genetically different defects. We have
identified the primary molecular alteration in two patients in whom clinic
al manifestations strongly reminiscent of a severe form of XP were unexpect
edly associated with the CS cellular phenotype and with a defect in the CSB
gene. Sequencing of the CSB-coding region in both cDNA and genomic DNA sho
wed that these patients had identical alterations to those in a patient wit
h the clinical features of the classical form of CS. These data, together w
ith fluorescence in situ hybridization analysis, demonstrated that the two
siblings with XP as well as the CS patient were homozygous for the same CSB
mutated allele, containing a silent C2830T change and a nonsense mutation
C2282T converting Arg735 to a stop codon. The finding that the same inactiv
ating mutation underlies different pathological phenotypes indicates that t
here is no simple correlation between the molecular defect and the clinical
features. Therefore, alterations in the CSB gene give rise to the same rep
air defect at the cellular level but other genetic and/or environmental fac
tors determine the pathological phenotype.