Biomedical subjects
J F Aitken
Publications and source records attributed to J F Aitken.
Ocular melanoma is not associated with CDKN2A or MC1R variants--a population-based study.
Germline variants in the melanocortin 1 receptor gene (MC1R) and the p16 gene (CDKN2A) are associated with an increased risk of cutaneous melanoma. The frequency of these germline variants was examined in a population-based, incident series of 62 ocular melanoma cases and ethnicity-matched population controls. In both cases and controls, 59% of individuals carried at least one MC1R variant and there were no significant differences in the frequency of any of the five most common variants of MC1R. We also found no significant differences between cases and controls in the frequency of any of the four most common variants of CDKN2A, and no melanoma case carried a deleterious germline CDKN2A mutation. Our findings argue against an important predisposing effect of the MC1R and CDKN2A genes for ocular melanoma.
A randomised trial of population screening for melanoma.
OBJECTIVES: Melanoma is a significant cause of morbidity and mortality worldwide and incidence is increasing. Survival after treatment is inversely related to the thickness of the tumour at diagnosis. Population screening has the potential to reduce mortality but there is no conclusive evidence of benefit. Such evidence can come best from a randomised trial. Here we describe the design of a community based randomised trial of a population screening programme for melanoma in Queensland, Australia and early results of the first phase of the trial. METHODS: A total of 44 communities (aggregate population 560 000 adults aged 30 years or more) will be randomised to receive either a community based screening programme for 3 years or normal practice. The screening programme promotes thorough skin self examination and whole body skin examination by a doctor and provides open access skin cancer screening clinics. In its first phase, the trial is underway in nine intervention and nine control communities. The primary outcome measure is mortality from melanoma during 15 years of follow up. RESULTS: The first phase of the trial has shown the feasibility of implementing a population skin screening programme including regular skin cancer screening clinics, and has shown the strong support of communities and doctors for the programme. There has been a significant 2.5-fold increase in participation in screening in the intervention communities in this first phase after the first 12 months of the trial and no significant increase in participation in screening in control communities during this period. CONCLUSIONS: The design of a community based randomised trial of screening for melanoma has been successfully peer reviewed and the intervention has been shown to be feasible in practice. This randomised trial may be one of the last opportunities to develop the evidence required for public health recommendations for population screening for melanoma.
Mutation analysis of the CDKN2A promoter in Australian melanoma families.
Approximately 50% of all melanoma families worldwide show linkage to 9p21-22, but only about half of these have been shown to contain germ line CDKN2A mutations. It has been hypothesized that a proportion of these families carry mutations in the noncoding regions of CDKN2A. Several Canadian families have been reported to carry a mutation in the 5' UTR, at position -34 relative to the start site, which gives rise to a novel AUG translation initiation codon that markedly decreases translation from the wild-type AUG (Liu et al., 1999). Haplotype sharing in these Canadian families suggested that this mutation is of British origin. We sequenced 1,327 base pairs (bp) of CDKN2A, making up 1,116 bp of the 5' UTR and promoter, all of exon 1, and 61 bp of intron 1, in at least one melanoma case from 110 Australian families with three or more affected members known not to carry mutations within the p16 coding region. In addition, 431 bp upstream of the start codon was sequenced in an additional 253 affected probands from two-case melanoma families for which the CDKN2A mutation status was unknown. Several known polymorphisms at positions -33, -191, -493, and -735 were detected, in addition to four novel variants at positions 120, -252, -347, and -981 relative to the start codon. One of the probands from a two-case family was found to have the previously reported Q50R mutation. No family member was found to carry the mutation at position -34 or any other disease-associated mutation. For further investigation of noncoding CDKN2A mutations that may affect transcription, allele-specific expression analysis was carried out in 31 of the families with at least three affected members who showed either complete or "indeterminate" 9p haplotype sharing without CDKN2A exonic mutations. Reverse transcription polymerase chain reaction and automated sequencing showed expression of both CDKN2A alleles in all family members tested. The lack of CDKN2A promoter mutations and the absence of transcriptional silencing in the germ line of this cohort of families suggest that mutations in the promoter and 5' UTR play a very limited role in melanoma predisposition.
Melanocortin-1 receptor polymorphisms and risk of melanoma: is the association explained solely by pigmentation phenotype?
Risk of cutaneous malignant melanoma (CMM) is increased in sun-exposed whites, particularly those with a pale complexion. This study was designed to investigate the relationship of the melanocortin-1 receptor (MC1R) genotype to CMM risk, controlled for pigmentation phenotype. We report the occurrence of five common MC1R variants in an Australian population-based sample of 460 individuals with familial and sporadic CMM and 399 control individuals-and their relationship to such other risk factors as skin, hair, and eye color; freckling; and nevus count. There was a strong relationship between MC1R variants and hair color and skin type. Moreover, MC1R variants were found in 72% of the individuals with CMM, whereas only 56% of the control individuals carried at least one variant (P<.001), a finding independent of strength of family history of melanoma. Three active alleles (Arg151Cys, Arg160Trp, and Asp294His), previously associated with red hair, doubled CMM risk for each additional allele carried (odds ratio 2.0; 95% confidence interval 1. 6-2.6). No such independent association could be demonstrated with the Val60Leu and Asp84Glu variants. Among pale-skinned individuals alone, this association between CMM and MC1R variants was absent, but it persisted among those reporting a medium or olive/dark complexion. We conclude that the effect that MC1R variant alleles have on CMM is partly mediated via determination of pigmentation phenotype and that these alleles may also negate the protection normally afforded by darker skin coloring in some members of this white population.
Genetic and environmental contributions to size, color, shape, and other characteristics of melanocytic naevi in a sample of adolescent twins.
The presence of melanocytic naevi is the strongest known risk factor for malignant melanoma. We have developed a computer imaging system with which it is possible to make quantitative measures of the size, color, and shape of pigmented lesions. The objective of this study was to examine the genetic and environmental contributions to these characteristics of naevi as measured by computer image analysis in a sample of adolescent twins. We captured video images of the 5 most atypical pigmented skin lesions (i.e., the largest, darkest, or most irregularly shaped) on each individual from 322 Australian adolescent twin pairs. Features extracted by computer image analysis for each lesion included color, size, symmetry, elongation, boundary irregularity, and edge distinctness. We found major genetic influences on the color and size of lesions accounting for between 40 and 80% of total variance. There were significant components of shared environmental influence (22-45% of total variance) for the color variables, with sun exposure the most obvious explanation. Differences between individuals in naevus color and size are largely genetic in origin although there are significant environmental contributions to color as well.
A major quantitative-trait locus for mole density is linked to the familial melanoma gene CDKN2A: a maximum-likelihood combined linkage and association analysis in twins and their sibs.
Important risk factors for melanoma are densely clustered melanocytic nevi (common moles) and mutations in the p16 (CDKN2A) gene. Nevi may be subclassified as raised or flat. In our sample, raised nevi were 27% of the total, and the two kinds had a correlation of.33. Correlations for total-nevus count (TNC) in 153 MZ and 199 DZ twin pairs were.94 and.60, respectively, which are compatible with a very-high degree of genetic determination. We hypothesized that some of the genetic variance might be due to variation in the p16 gene. Analysis of linkage to a highly polymorphic marker (D9S942), located close to p16, detected quantitative-trait-loci (QTL) effects accounting for 27% of variance in TNC, rising to 33% if flat but not raised moles were considered. Total heritability was higher for raised (.69) than for flat (.42) moles, but QTL linkage was 0 for raised moles, whereas it accounted for 80% of the heritability of flat moles; additionally, family environment accounted for only 15% of variance in raised versus 46% in flat moles. These findings suggest that raised and flat nevi have very different etiologies. Longer alleles at D9S942 were associated with higher flat-mole counts, and a novel modification to a within-sibship association test showed that this association is genuine and not due to population stratification, although it accounts for only 1% of total variance. Since germline mutations in the exons of CDKN2A are rare, it is likely that variants in the noncoding regions of this gene, or in another gene nearby, are responsible for this major determinant of moliness and, hence, of melanoma risk.
Segregation analysis of cutaneous melanoma in Queensland.
To investigate whether the familial clustering of cutaneous melanoma is consistent with Mendelian inheritance of a major autosomal gene, maximum likelihood segregation analyses were performed in a population-based sample of 1,912 families ascertained through a proband with melanoma diagnosed in Queensland between 1982 and 1990. Analyses were performed with the S.A.G.E. statistical package, using the REGTL program for a binary trait with a variable age of onset. We sought medical confirmation for all family members reported to have had melanoma, and only medically verified cases among relatives were included in the analyses. The hypothesis of codominant Mendelian inheritance gave a significantly better fit to the data than either dominant or recessive Mendelian inheritance, or environmental transmission. Overall, both Mendelian inheritance of a single major gene, and purely environmental transmission were rejected (P < 0.001). In both the single major gene and environmental models, there was strong evidence of familial dependence in melanoma occurrence (P < 0.001). These results are consistent with reported genetic heterogeneity in melanoma inheritance and suggest that other familial factors, such as pigmentation, skin type, and sun exposure habits, may play an important role in the familial clustering of melanoma.
Reliability of computer image analysis of pigmented skin lesions of Australian adolescents.
BACKGROUND: The diagnosis of melanomas at an early stage is associated with improved survival, so the recognition of changes in pigmented skin lesions over time is important. We have developed a computer imaging system with the aim of assisting clinicians in differentiating early melanomas from benign pigmented skin lesions. The objective of this study was to investigate the system's reliability over time in measuring diagnostic characteristics of pigmented skin lesions, including their color, size, shape, and distinctness of boundary. METHODS: We captured video images of 5 lesions, all larger than 2 mm in greatest dimension, on each of 66 Australian adolescents on 2 occasions approximately 1 month apart. Features extracted by computer image analysis included area, perimeter, and regularity of outline of the lesions, the mean and standard deviation of reflectance at red, green, and blue wavelengths, and the mean and standard deviation of the gradients of red, green, and blue reflectance at the lesion boundary. RESULTS: All measurements showed moderate to high reliability (intraclass correlation coefficients 0.66-0.94), except for the standard deviations of the color gradients, whose reliability improved to moderate levels (0.68-0.71) when the mean of 5 lesions was considered. For most outcomes, reasonable within subject reliability was achieved when five lesions per subject were measured. CONCLUSIONS: These results, in combination with previous work demonstrating the reasonable ability of this computer imaging system to discriminate between malignant melanomas and other pigmented lesions, indicates that the system has the potential to become a useful tool for clinicians in following people with pigmented lesions over time to detect early malignant changes.
Mechanism of NO-induced oxidation of myoglobin and hemoglobin.
Nitric oxide (NO) has been implicated as mediator in a variety of physiological functions, including neurotransmission, platelet aggregation, macrophage function, and vasodilation. The consumption of NO by extracellular hemoglobin and subsequent vasoconstriction have been suggested to be the cause of the mild hypertensive events reported during in vivo trials of hemoglobin-based O2 carriers. The depletion of NO from endothelial cells is most likely due to the oxidative reaction of NO with oxyhemoglobin in arterioles and surrounding tissue. In order to determine the mechanism of this key reaction, we have measured the kinetics of NO-induced oxidation of a variety of different recombinant sperm whale myoglobins (Mb) and human hemoglobins (Hb). The observed rates depend linearly on [NO] but show no dependence on [O2]. The bimolecular rate constants for NO-induced oxidation of MbO2 and HbO2 are large (k.ox,NO = 30-50 microM-1 s-1 for the wild-type proteins) and similar to those for simple nitric oxide binding to deoxygenated Mb and Hb. Both reversible NO binding and NO-induced oxidation occur in two steps: (1) bimolecular entry of nitric oxide into the distal portion of the heme pocket and (2) rapid reaction of noncovalently bound nitric oxide with the iron atom to produce Fe(2+)-N=O or with Fe(2+)-O-O delta- to produce Fe(3+)-OH2 and nitrate. Both the oxidation and binding rate constants for sperm whale Mb were increased when His(E7) was replaced by aliphatic residues. These mutants lack polar interactions in the distal pocket which normally hinder NO entry into the protein. Decreasing the volume of the distal pocket by replacing Leu(B10) and Val(E11) with aromatic amino acids markedly inhibits NO-induced oxidation of MbO2. The latter results provide a protein engineering strategy for reducing hypertensive events caused by extracellular hemoglobin-based O2 carriers. This approach has been explored by examining the effects of Phe(B10) and Phe(E11) substitutions on the rates of NO-induced oxidation of the alpha and beta subunits in recombinant human hemoglobin.
The Queensland Familial Melanoma Project: study design and characteristics of participants.
Family history of melanoma is associated with an increased risk for the disease. Neither the relative contributions of genetic and shared environmental factors to familial risk nor how genetic susceptibility is mediated are known. The Queensland Familial Melanoma Project was undertaken to investigate (a) the role of genetic susceptibility as indicated by skin type, pigmentation and the prevalence of naevi and (b) exposure to solar ultraviolet radiation, and their interaction in the aetiology of familial melanoma. After obtaining doctor's consent, a brief family history questionnaire was mailed to all Queensland residents with a first primary cutaneous melanoma diagnosed between 1982 and 1990. Detailed information on melanoma history and standard melanoma risk factors was sought from all responding twins and familial cases, from a sample of non-familial cases and from cases' relatives. Medical confirmation was sought for all relatives reported to have had melanoma. The final sample comprises 15,907 persons in the 1,912 families of 2,118 melanoma cases, including 509 families in which there are two or more individuals with confirmed melanoma. Melanoma history and risk factors were obtained for 9,746 relatives, including 94 twins of cases. This is the largest family and twin study of cutaneous melanoma yet conducted in an unselected, geographically-defined population. We describe the design of the study and the characteristics of the total study population.
Accuracy of case-reported family history of melanoma in Queensland, Australia.
A positive family history is used in clinical practice as an indication of increased melanoma risk, yet there are no data on the accuracy of reported family histories of melanoma. The validity of case-reported family history of melanoma was assessed in the course of a family and twin study of melanoma in Queensland, Australia, conducted among the families of 2,118 melanoma cases diagnosed in Queensland between 1982 and 1990. A total of 913 melanoma cases made 1,267 reports of melanoma among their first-degree relatives. A total of 1,040 of these reports were checked, first through relatives themselves and then, if the relative also said they had had melanoma, through the relative's medical records. Medical confirmation of melanoma as the diagnosis was obtained for 623 reports (59.9%; 95% confidence interval 56.9-62.9): a false-positive reporting rate by cases of 40.1%. The level of false-positive reporting was lower for cases under 70 years of age, for women, for cases whose own diagnosis of melanoma was more than 5 years earlier, and for cases with three or more relatives with melanoma. Media campaigns in Queensland aimed at increasing skin cancer awareness, and confusion between melanoma and other more common actinic neoplasma (basal and squamous cell carcinomas), may partly explain the high false-positive reporting rate observed here. For this reason, It is difficult to generalize these findings to northern hemisphere populations where skin cancer is not such an important public health issue.
Risk of colorectal adenomas in patients with a family history of colorectal cancer: some implications for screening programmes.
BACKGROUND AND AIMS: Most colorectal cancers (CRC) arise in colorectal adenomas. A case-control study was conducted to see whether a family history of CRC is associated with a higher prevalence of colorectal adenomas. SUBJECTS: Subjects were drawn from all patients who underwent colonoscopy at the Royal Brisbane Hospital between 1980-1982 and 1985, and included 141 cases with colorectal adenomas diagnosed at colonoscopy and 882 controls who were free of polyps at colonoscopy. METHODS: The prevalence of family history of CRC was compared between patients with adenomas and negative colonoscopy controls. RESULTS: Overall, patients with one first degree relative with CRC were at no greater risk for adenomas at colonoscopy than patients with no family history (odds ratio (OR) = 0.8, 95% confidence intervals (CI) = 0.4, 1.5). Patients with two or more affected first degree relatives had a more than doubled risk for adenomas (OR = 2.3, 95% CI = 0.5, 8.2), and were also more likely to carry moderately or severely dysplastic adenomas (OR = 14.1, 95% CI = 2.0, 62.9). CONCLUSIONS: These findings are consistent with the hypothesis that some families, in addition to those with familial adenomatous polyposis, have an increased susceptibility to develop colorectal adenomas, and that adenomas in such families may have a greater tendency to undergo malignant transformation.
Heterogeneity of melanoma risk in families of melanoma patients.
While it is recognized that relatives of melanoma patients are at increased risk for this disease, the source and extent of variation in melanoma risk between families of melanoma cases is unknown. Heterogeneity of familial melanoma risk was assessed among the families (comprising 7,666 first-degree relatives) of 1,149 cutaneous melanoma cases diagnosed in Queensland, Australia, between 1982 and 1987. The measure of familial melanoma risk was based on the number of cases of melanoma in the family in excess of those predicted from the age-, sex-, and birth cohort-specific cumulative incidences of melanoma among all relatives in the sample. Probands over-reported melanoma occurrence among their relatives, with a false positive reporting rate of 44.5% (216 false reports out of 485). Only medically verified cases among relatives were included in the analysis. There was statistically significant heterogeneity in family risk, with 53 (4.7%) of the total 1,116 unrelated families containing significantly more melanoma cases than expected considering the size of the family, and the age, sex, and birth cohort distributions of family members. In univariate analyses, members of the high-risk families were significantly more likely to have poor ability to tan, a propensity to sunburn, fair skin color, red hair, and many melanocytic nevi. When all variables were included simultaneously in a multiple logistic regression model, only the associations with tanning ability, skin color, and number of nevi remained significant. There were no significant differences overall between high-risk and other families in the sites and ages at diagnosis of melanoma, although melanomas on variably sun-exposed sites (trunk and legs) were diagnosed earlier in the high-risk families, independent of the stage at diagnosis.
Comparability of naevus counts between and within examiners, and comparison with computer image analysis.
In the course of an investigation of melanocytic naevus development in Queensland, Australia, whole-body naevus counts of 66 adolescents were performed separately by two nurse examiners on two occasions on average 4 weeks apart. There was good agreement between the two examiners for counts of total naevi on the whole body (intra-class correlation coefficient = 0.96) and at selected subsites (face, neck, back, upper arms, lower arms). Agreement was lower when raised naevi only were counted (0.83). Intra-examiner repeatability was high for both nurses, particularly for the more experienced examiner (intra-class correlation coefficients = 0.98 and 0.91 for total naevi on the whole body), and was consistently better when all naevi were counted rather than naevi of a particular size. Independent counts of naevi on the back using a computer imaging technique were reproducible (intra-class correlation coefficient = 0.92), but showed only moderate agreement with counts by the nurse examiners. Overall, these results demonstrate high comparability of naevus counts between and within similarly trained examiners. They do not support the common practice in epidemiological studies of restricting counts to naevi larger than 2 mm, or of counting raised naevi only.
Comparability of surrogate and self-reported information on melanoma risk factors.
Surrogate reports by patients about their relatives, and vice versa, are potentially of great use in studies of the genetic and environmental causes of the familial aggregation of cancer. To assess the quality of such information in a family study of melanoma aetiology in Queensland, Australia, the authors compared surrogate reports with self-reports of standard melanoma risk factors obtained by mailed self-administered questionnaire. There was moderate agreement between surrogate reports provided by the cases and relatives' self-reports for questions on ability to tan (polychoric correlation coefficient (pc) = 0.60), skin colour (pc = 0.57), average propensity to burn (pc = 0.56), and hair colour at age 21 (kappa coefficient = 0.55), although relatives in the extreme risk factor categories were misclassified by surrogates at least half of the time. Agreement was lower for questions on degree of moliness (pc = 0.45), tendency to acute sunburn (pc = 0.42), and number of episodes of painful sunburn (pc = 0.23). The quality of relatives' surrogate reports about cases was similar to that of cases' surrogate reports about relatives. Cases who reported a family history of melanoma provided better surrogate information than did cases who indicated no family history, and female cases provided better surrogate reports than did males. Cases were better able to report for their parents and children than for their siblings. The authors conclude that when the use of surrogate reports of melanoma risk factors is unavoidable, results should be interpreted cautiously in the light of potentially high rates of misclassification. In particular, surrogate reports appear to be a comparatively poor measure of self-assessment of number of moles, the strongest known phenotypic indicator of melanoma risk, and may bias comparisons between families with and without a history of melanoma.
The gene encoding the phosphatidylinositol transfer protein is essential for cell growth.
Phosphatidylinositol transfer proteins (PI-TPs) catalyze the transfer of phosphatidylinositol and phosphatidylcholine between membranes in vitro. However, the in vivo function of these proteins is unknown. In this paper, we use a combined biochemical and genetic approach to determine the importance of PI-TP in vivo. An oligonucleotide based on the amino-terminal sequence of the PI-TP from Saccharomyces cerevisiae was used to screen a yeast genomic library for the gene encoding PI-TP (PIT1 gene). Positive clones showed overproduction of transfer activities and transfer protein in the 100,000 x g supernatants. The 5' terminus of the PIT1 gene correlates with the predicted codons for residues 3-30 of the determined protein sequence. A putative intron is located between the codons for residues 2 and 3 of the protein sequence. The codons for the first two amino acids of the protein and the presumptive initiation methionine precede the intron. Tetrad analysis of a heterozygous diploid (PIT1/pit1::LEU2) revealed that the PIT1 gene is essential for cell growth. Nonviable spores could be rescued by transformation of the above diploid prior to sporulation, with a plasmid-borne copy of the wild type gene.
Antisera to synthetic peptide recognize high molecular weight enkephalin-containing proteins.
Antisera to a synthetic peptide corresponding to the 95-117 sequence of proenkephalin were used to develop a sensitive radioimmunoassay. Gel-filtration of acid extracts of bovine adrenal medulla and purified chromaffin granules revealed that the antisera recognized high molecular weight material (Mr approximately 5,000-30,000). The material in peak I ( Mr 20 ,000-30,000) and peak II (Mr 10,000-20,000) was further purified by immunoaffinity chromatography. Sequential digestion of each of these fractions with trypsin and carboxypeptidase B generated immunoreactive Met-enkephalin. This study demonstrates that antisera against a synthetic peptide cross-react with high molecular weight enkephalin-containing precursors, validating the use of these antisera in studies of enkephalin biosynthesis.