No abstract

Chromosome 9p21 is frequently deleted in malignant melanoma, and one familial malignant melanoma gene has been linked to 9p21-22. Recently, the cyclin D-dependent kinase inhibitors (CDKIs) p16INK4a and p15INK4b have been localized within chromosome 9p21, and the presence of p16INK4a point mutations has been demonstrated in familial melanoma and melanoma cell lines in vitro. To analyse the role of these CDKIs in sporadic human cutaneous non-metastatic malignant melanoma, we examined 36 primary tumour specimens representing different stages of melanoma progression and their corresponding normal skin samples for the three mechanisms of CDKI inactivation described so far. Homozygous codeletion of the p16INK4a and the p15INK4b gene was detected by Southern blot analysis in two tumour samples. By direct sequencing of polymerase chain reaction (PCR)-amplified microdissected genomic DNA; no somatic or germline p16INK4a point mutations or small deletions were detected in the remaining 34 tumour samples; one individual exhibited the previously described germline codon 148 (Ala-->Thr) polymorphism. In these tumour specimens, comparative semiquantitative reverse PCR analysis of p16INK4a transcript levels revealed no evidence for repression of p16INK4a gene transcription and thus for p16INK4a promoter inactivation by DNA methylation. These results indicate homozygous p16INK4a and p15INK4b loss to occur in a subset of cutaneous melanomas and suggest, in view of the frequent loss of heterozygosity on chromosome 9p21, the presence of another tumour suppressor gene within this chromosomal region.

Friedreich's ataxia (FA) is an autosomal recessive disease that has been attributed to a GAA triplet repeat expansion in the first intron of the X25/frataxin gene. Impaired glucose tolerance is present in up to 39% of FA patients, and clinically apparent diabetes is seen in ~18% of the affected individuals. Subjects carrying the X25/frataxin GAA repeat in a heterozygous state do not develop FA and, therefore, represent an ideal model to study the underlying metabolic defects that contribute to the diabetes associated with this disorder. In the present study, we have compared 11 first-degree relatives of FA patients (i.e., parents or heterozygous siblings of FA patients) with matched normal control subjects to study the parameters of glucose metabolism. An oral glucose tolerance test revealed diabetes in one of the heterozygous subjects who was excluded from further analyses. Using an octreotide-based quantification of insulin sensitivity, 8 of the remaining 10 study subjects showed pronounced insulin resistance, reflecting a significant difference from the control group (P = 0.001). In conclusion, a heterozygous expansion of the X25/frataxin GAA repeat in healthy individuals is associated with insulin resistance and might be considered a genetic co-factor in the pathogenesis of mitochondrial subtypes of diabetes. Diabetes 49:1604-1607, 2000 F riedreich's ataxia (FA) is phenotypically characterized by progressive ataxia and other neurological alterations in association with hypertrophic cardiomyopathy. The vast majority of FA patients carry a homozygous expansion of an intronic GAA tract of the X25/frataxin gene (1) leading to interference with the transcription of the frataxin gene (2) and subsequently decreasing expression of the frataxin protein (3). Frataxin is expressed in a wide variety of tissues, exhibits mitchondrial localization, and appears to be essential for embryonic development (4) in mice. Frataxin is most abundant in tissues with high metabolic activity, including skeletal muscle and brown fat (5). The characterization of the yeast frataxin homolog suggests a central role in oxidative phosphorylation (6). Furthermore, frataxin was proposed to regulate mitochondrial iron content (7,8) and to decrease oxidative damage to the cell (9,10). Frataxin is a mitochondrial protein that is significantly reduced in FA patients because of decreased transcription subsequent to expanded intronic GAA repeats on both copies of the X25/frataxin gene. Heterozygous carriers for this expansion are phenotypically normal but presumably exhibit a decreased expression of frataxin (2,11). In the present study, these heterozygous individuals were evaluated for alterations in glucose metabolism, specifically incidence of diabetes and insulin resistance.First, first-degree relatives of FA patients were genotyped, as described in RESEARCH DESIGN AND METHODS, to assure the presence of GAA expansions, especially in siblings of the patients. Eleven subjects from 4 different unrelated families were analyzed (8 parents and 3 sibli...

Summary:We analysed data from 64 patients with Wegener's granulomatosis to determine predictor variables of outcome. The mean period of observation after the diagnosis had been established was 3.2 (range 0.1-11.2) years. At the time of diagnosis, 15 (23%) patients had only local symptoms. The disease was generalized to multiple organs in 49 (77%) patients. Renal biopsies were obtained in 33 patients; 13 (39%) had extracapillary glomerulonephritis, which was the most common renal lesion. All but three patients received immunosuppressive therapy. At time of follow-up, 17 (27%) patients were in complete, and 26 (40%) in partial remission. We employed a Kaplan Meier analysis to identify predictor variables of outcome. Renal involvement, initial creatinine concentration, serum albumin or total protein concentration, leukocyte count and erythrocyturia proved to be predictor variables. These variables may be of value in guiding the intensity of treatment in patients with Wegener's granulomatosis.