Psoriasis is an inflammatory skin disorder affecting approximately 3% of the population. Genetic studies published so far have shown a complex genetic inheritance with heterogeneity and a putative major susceptibility locus in the HLA region on chromosome 6. We have collected a large amount of material consisting mostly of small nuclear families in order to perform a genome-wide scan for psoriasis-associated genes. In order to focus the scan properly on possible candidate regions, we performed a cytogenetic analysis of 477 unrelated psoriatics. We divided our findings into sporadic, affecting a minor fraction of the cells, and constitutional, ie they were present in all cells examined. We found three cases of balanced translocation, all of which involved chromosome 11q. Two of these had a breakpoint in q12-13, whilst one involved the telomeric part of chromosome 11q. In order to characterise further the breakpoint on 11q12-13, we used bacterial artificial chromosomes (BACs) analysed by fluorescent in situ hybridisation (FISH). We were able to show that the persons had a close, but not identical breakpoints; they were separated by at least 5 cM. The major atopy locus is located in this region, as well as a locus for insulin-dependent diabetes mellitus, both being conditions with a pathogenetic mechanism involving antigen presentation.

Chromosome analyses were performed un 52 mildly mentally retarded adults and a control group representing the non-retarded population. Chromosomal aberrations were found in 19-2% of the mentally retarded and in 1 9% of the controls. The aberrations in the retarded group consisted of trisomy 21, fragile-X, sexchromosome aberrations and balanced translocations. The Index group included a man with a fragile site Xp22.1. The aberration in the control group consisted of a karyotype with an extra marker chromosome.

One of the major problems in preparation of chromosomes from lymphocyte cultures for routine cytogenetic analysis is to obtain slides with many mitoses exhibiting sufficient spread to facilitate high resolution G-banding, even when working with prometaphases. Difficulties in finding simple and effective methods for preparing maximum numbers of well-spread metaphases and prometaphases have led to considerable experimentation in our laboratory. The addition of methotrexate (MTX) and thymidine (BARNES and MALTBY 1986;YUNIS 1976) or MTX, bromodeoxyuridine (BrdU), and actinomycin (YUNIS 1981), or ethidium bromide (IKEUCHI 1984) to induce prometaphases has given irregular results, while repeated fixations to increasc spreading of chromosomes and removal of proteins that interfere with bdnding. have resulted in a loss of many mitoses.To remove excess proteins and red blood cells, thereby reducing the time and number of fixations, we have utilized 6 % acetic acid for prefixing. This treatment eliminates the need of more than one fixation and results in a great number of wellsprcad mitoses at various stages. We have also noted that the temperature during colcemid treatment is very important for the spreading of the mitoses.This report describes a simplified and efficient routine method for producing a high frequency of metaphase and prometaphase plates from human lymphocyte cultures. Materials and methodsFive blood samples from the laboratory's routine testing were randomly selected. The lymphocyte cultures were established by inoculating 0.5 ml * Correspondence 10 Tonnie Johannesson whole heparinized blood into a test tube (Falcon Tissue Culture Tube, 16 x 25 mm) containing 10 ml Parker 199 (SBL) supplemented with 10 YO Fetal calf serum, 2 % Phytohemagglutinin M (DIFCO), and antibiotics. In the case of small infants, capillary samples can be taken by dropping 5-10 drops of blood directly into a test tube containing 10 ml prewarmed medium.The cultures were incubated in a 37°C incubator without CO, for 72 or 96 h. The test tubes must have caps tightly closed.One and a half hours before harvest, colcemid (10 pg/ml GIBCO) was added to a final concentration of 0.5 pg/ml. Extreme care was taken that the temperature did not drop below 37°C during colcemid treatment. The cells were harvested by centrifugation at 1000 rpm for 10 min. Pelleted cells were resuspended in 6 ml hypotonic solution ( 1: 1 solution for 0.4 O/ O KCI and 0.4 O/ O sodium citrate) followed by a 15 min incubation at 37°C.After centrifugation, the cell pellet was resuspended in 5 ml 6 YO acetic acid under constant agitation. After 5 min at room temperature the cells were pelleted and resuspended in 9 m l cold fixative ( 1 :3 glacial acetic acid:absolute ethanol) followed by immediate centrifugation. The cell pellet was finally resuspended in 0.5 ml cold fixative, and slides were prepared by dropping only one drop of cell suspension onto a cold, wet slide, which then was air dried. When necessary, the chromosome spreading could be increased by adding 0.25 mi fi...