High mutation frequency at Ha-ras exons 1-4 in squamous cell carcinomas from PUVA-treated psoriasis patients.

Clinical follow-up studies have revealed that PUVA-treated patients are at increased risk of skin cancer, particularly squamous cell carcinoma (SCC). However, since psoralen and UVA (PUVA) is not only a potent mutagen and carcinogen but also an immunosuppressor, and since other (co)carcinogenic factors often exist in psoriasis patients, the exact causes and mechanisms of PUVA-associated SCC are still not completely understood. In order to fill this gap the tools of molecular epidemiology are being used to study the SCC mutational spectra of p53 and Ha-ras, two of the most commonly mutated genes in human cancers. A previous mutation analysis revealed that SCC in PUVA-treated patients often carried mutated p53 genes and that many of the mutations had the UV fingerprint (i.e. C-->T or CC-->TT transitions at dipyrimidine sites). In the present study DNA-sequencing analysis revealed a total of 18 Ha-ras missense or nonsense mutations at exons 1-4 in 13 of 17 SCC (76%) from 8 of 11 (73%) PUVA-treated psoriasis patients. Six of the 18 mutations (33%) were of UV-fingerprint type (C-->T transitions), five (28%) were at 5'-TpG sites (i.e. potential psoralen-binding sites and thus potentially caused by PUVA) and seven were of other type (39%), including six G:C-->T:A transversions at hotspot codon 12. In addition, in the case of 6 of the 11 subjects (55%) both tumor and normal skin samples contained a T:A-->C:G base change at codon 27 (a 5'-ATT site), a change previously hypothesized to be a possible silent Ha-ras polymorphism at one allele. When we compared the present Ha-ras mutation spectrum with the p53 mutation spectrum from a previous study of the samples, we found that approximately half of the tumors harbored mutations in both Ha-ras and p53. Together, our results indicate that Ha-ras mutations are present in a large proportion of PUVA-associated SCC and that UVB, PUVA and other agents may induce Ha-ras mutations and act together with p53 in the formation of SCC in psoriasis patients.

Ultraviolet exposure as the main initiator of p53 mutations in basal cell carcinomas from psoralen and ultraviolet A-treated patients with psoriasis.

Basal cell carcinoma, the most frequent skin cancer in humans, is often linked to chronic sun exposure. In psoralen and ultraviolet A-treated psoriatic patients, basal cell carcinomas may occur even more frequently; however, the exact etiology and mechanisms of tumorigenesis in psoriatic patients are unclear because psoralen and ultraviolet A is not only a carcinogen but also an immunosuppressor and because psoralen and ultraviolet A-treated psoriatic patients often have other (co)carcinogenic risk factors (e.g, therapeutic exposure to ultraviolet B, X-ray radiation, arsenic, tar, and/or chemotherapeutic agents such as methotrexate). In this study, we analyzed the DNA of 13 basal cell carcinomas from five psoralen and ultraviolet A-treated psoriatic patients for mutations of the p53 tumor suppressor gene. DNA sequencing revealed a total of 11 mis-sense, two non-sense, and four silent mutations in seven of the 13 basal cell carcinomas (54%). Of the 13 total mis-sense or non-sense mutations, 12 (92%) occurred at dipyrimidine sites and nine (69%) were of the ultraviolet fingerprint type (eight C-->T transitions and one CC-->TT transition). Three of the C-->T transitions occurred at dipyrimidine sites opposite a 5'-TpG sequence (a potential psoralen-binding site and target for psoralen and ultraviolet A mutagenesis). Thus, whether these mutations were induced by ultraviolet or psoralen and ultraviolet A was not clear. In addition, two other mutations (15%) occurred at 5'-TpG sites, one (8%) occurred at a 5'-TpA site (the most frequent site of psoralen binding and mutagenesis in cell and murine studies), and one (8%) involved a G-->T transversion. These results suggest that (i) the major initiator of p53 mutations in basal cell carcinoma in psoralen and ultraviolet A-treated psoriasis patients is environmental and/or therapeutic ultraviolet(B) exposure, and that (ii) psoralen and ultraviolet A itself causes only a smaller portion of p53 mutations in psoralen and ultraviolet A-associated basal cell carcinomas.

Mutation analyses in 17 patients with deficiency in acid beta-galactosidase: three novel point mutations and high correlation of mutation W273L with Morquio disease type B.

An inherited deficiency in beta-galactosidase can result in GM1 gangliosidosis, with several phenotypes of generalized or chronic psychomotor deterioration, as well as in Morquio disease type B, a characteristic mucopolysaccharidosis free of neurological symptoms. We performed mutation analyses in 17 juvenile and adult patients from various European regions with a deficiency in beta-galactosidase and skeletal abnormalities. Fifteen of these had the Morquio B phenotype and have remained neurologically healthy until now while the two others exhibited psychomotor retardation of juvenile onset. A two-base substitution (851-852TG-->CT; W273L) was present in 14 of the 15 Morquio B cases. Even if one excludes alleles from patients with possible common descent, there was a much higher frequency (79%) among those with Morquio B phenotype for the W273L mutation than previously reported in the literature (37%). That the Morquio phenotype is also expressed in heterozygotes for W273L and alleles typically found in GM1 gangliosidosis makes it possible to predict the phenotype and reliably detect heterozygotes. A single French patient had a novel missense point mutation (Q408P) together with a known mutation (T500A) while the mentally retarded patients were both heterozygous for two mutations known in chronic GM1 gangliosidosis together with two novel missense point mutations (Y270D and H281Y) in the vicinity of W273L. Our results confirm the high impact of Trp 273 for the function of beta-galactosidase and the expression of the Morquio B phenotype. In addition, a second domain around the amino acids 400-500 may also be of significance.