Aad Tibben | Leiden University (original) (raw)
Papers by Aad Tibben
Brain, 2000
Several mutations in the amyloid precursor protein (APP) gene may lead to either Alzheimer&am... more Several mutations in the amyloid precursor protein (APP) gene may lead to either Alzheimer's disease or cerebral haemorrhage due to congophilic amyloid angiopathy (CAA). A single family is known in which both types of pathology are expressed because of a missense mutation at codon 692 of the APP gene (APP692). Here we describe the clinical and pathological expression of APP692 in eight patients with the mutation. Furthermore, 21 first-degree relatives with an a priori risk of 50% of being a carrier were tested for the APP692 mutation and studied for presymptomatic signs by neurological examination, neuropsychological testing and brain MRI. Patients with APP692 presented with haemorrhage, dementia or both. The dementia in patients with the APP692 mutation was compatible with Alzheimer's disease both clinically and neuropathologically. Of the 21 healthy relatives at 50% risk, five carried the APP692 mutation. The presymptomatic carriers showed a subtle, non-significant impairment of cognitive function compared with relatives without APP692. A significant increase in the number of periventricular and subcortical white matter lesions at young age was seen in presymptomatic carriers (mean age 26.4 years). The findings of this study suggest that a single (genetic) mechanism may underlie the pathology of Alzheimer's disease and CAA. These diseases are manifested subclinically by white matter pathology. Further insight into the relationship between CAA and Alzheimer's disease may provide clues about the aetiology of Alzheimer's disease.
Psycho-Oncology, 2005
Since p16-Leiden presymptomatic testing for hereditary melanoma has become available in the Nethe... more Since p16-Leiden presymptomatic testing for hereditary melanoma has become available in the Netherlands, the benefits and risks of offering such testing are evaluated. The current paper investigated why the non-participants were reluctant to participate in genetic testing. Sixty six eligible individuals, who were knowledgeable about the test but had not participated in genetic testing by January 2003, completed a self-report questionnaire assessing motivation, anxiety, family dynamics, risk knowledge and causal attributions. Non-participants reported anxiety levels below clinical significance. A principal components analysis on reasons for non-participation distinguished two underlying motives: emotional and rational motivation. Rational motivation for non-participation was associated with more accurate risk knowledge, the inclination to preselect mutation carriers within the family and lower scores on anxiety. Emotional motivation for non-participation was associated with disease misperceptions, hesitation to communicate unfavourable test results within the family and higher scores on anxiety. Rational and emotional motivation for non-participation in the genetic test for hereditary melanoma was found. Emotionally motivated individuals may be reluctant to disseminate genetic risk information. Rationally motivated individuals were better informed than emotionally motivated individuals. It is suggested that a leaflet is added to the invitation letter to enhance informed decision-making about genetic testing.
Psycho-Oncology
Prospective studies regarding the psychosexual impact after different types of breast reconstruct... more Prospective studies regarding the psychosexual impact after different types of breast reconstruction (BR) are scarce. The impact of either implant or deep inferior epigastric artery perforator (DIEP) flap BR on body image and sexual relationship satisfaction was investigated in time. At baseline, 98 women opting for delayed implant or DIEP flap BR after mastectomy for breast cancer completed a survey. The majority was followed up at 6 months (96%) and 20 months (86%) postoperatively. Questionnaires included the body image scale, Dutch Relationship Questionnaire, Short Form - 36 Health Survey and the Impact of Event Scale. Mixed modeling analyses indicated that preoperative body image improved significantly after 20 months (p < 0.001), and there was no statistically significant difference between the two types of BR. A better body image was related to a better general mental health (p = 0.02), less cancer distress (p < 0.001) and a higher partner relationship satisfaction (p &l...
European Journal of Human Genetics, 2013
The Lancet
197 the treating physician. With the possible exception of tubal ligation, there is always a risk... more 197 the treating physician. With the possible exception of tubal ligation, there is always a risk, albeit low, of conception during treatment. The physician should then explain to the couple the risks and advantages of treatment, so that the partners agree to the use of additional and effective contraceptive measures. If conception does occur, abortion should be considered.
The Lancet
Marshall JB. Tuberculosis of the gastrointestinal tract and peritoneum. Am J Gastroenterol 1993; ... more Marshall JB. Tuberculosis of the gastrointestinal tract and peritoneum. Am J Gastroenterol 1993; 88: 989-99. 3 Puylaert JBCM, Vermeyden RJ, van der Werf SDJ, Doornbos L, Koumans RKJ. Incidence and sonographic diagnosis of bacterial ileocaecitis masquerading as appendicitis. Lancet 1989; ii: 84-86.
Nederlands tijdschrift voor geneeskunde
The American Journal of Human Genetics
Attitudes toward predictive testing programs, in individuals who choose not to undertake the test... more Attitudes toward predictive testing programs, in individuals who choose not to undertake the test (i.e., nonparticipants), may be influenced by fears of an unfavorable result. The reasons not to participate in predictive testing programs for Huntington disease (HD) were studied in members of the Dutch Huntington Association who were at 50% risk. They had completed the same baseline psychological questionnaires as had the participants in the Dutch DNA-testing program. The group of 34 nonparticipants was similar to the tested participants in the Dutch predictive testing program, with respect to average age (31.1 years), male:female ratio (1:2), the frequency of a stable relationship (70%), and level of education (67% had high school education or higher). Testing did not seem to be a realistic option for nonparticipants for improving their quality of life. In comparison with participants, nonparticipants had a significantly more pessimistic outlook on themselves and their futures. When...
Genetics in Medicine
To test the "false-reassurance hypothesis," which suggests that women who receive an un... more To test the "false-reassurance hypothesis," which suggests that women who receive an uninformative BRCA1/2 test result may incorrectly conclude that they no longer have an elevated risk, with possible harmful consequences for adherence to breast surveillance guidelines. A prospective questionnaire design was used to compare 183 women with an uninformative BRCA test result (94 affected and 89 unaffected) with 41 proven BRCA mutation-carriers and 49 true negatives before and after BRCA1/2 test disclosure. After DNA-test disclosure, test applicants differed from each other with regard to their perception of the likelihood of carrying a deleterious gene (P < 0.0001). The BRCA mutation carriers reported the highest perceived likelihood and the true negatives reported the lowest. Compared to the predisclosure measures, women who received an uninformative DNA test result reported a lower perceived risk after disclosure (P < 0.0001), suggesting a relatively high level of rea...
Journal of Medical Genetics, 1998
The first comparative study on predicting post-test distress (conceptualised by intrusion and avo... more The first comparative study on predicting post-test distress (conceptualised by intrusion and avoidance, measured with the Impact of Event Scale) after presymptomatic genetic testing for Huntington's disease (HD, n=25), cancer syndromes (familial adenomatous polyposis (FAP, n=23)), and hereditary breast and ovarian cancer (HBOC, n=10) is reported. The variables with the highest predictive potential of post-test distress are presented. Participants who
Journal of Medical Genetics, 1997
In a comparative study on the effects of predictive DNA testing for late onset disorders, pre-tes... more In a comparative study on the effects of predictive DNA testing for late onset disorders, pre-test psychological distress was assessed in people at risk for Huntington's disease (HD, n = 41), cerebral haemorrhage (HCHWA-D, n = 9), breast and ovarian cancer (HBOC, n = 24), and polyposis coli (FAP, n = 45). Partners, if available, also participated in the study.
Journal of plastic, reconstructive & aesthetic surgery : JPRAS, Jan 19, 2015
Journal of medical genetics, 1999
Presymptomatic DNA testing for autosomal dominant hereditary breast/ovarian cancer (HBOC) became ... more Presymptomatic DNA testing for autosomal dominant hereditary breast/ovarian cancer (HBOC) became an option after the identification of the BRCA1 and BRCA2 genes in 1994-1995. Healthy female mutation carriers have a high lifetime risk for breast cancer (56-87%) or ovarian cancer (10-60%) and may opt for intensive breast and ovary surveillance or prophylactic surgery (mastectomy/oophorectomy). We studied general and cancer related distress in 85 healthy women with a 25% or 50% risk of being carrier of a BRCA1/BRCA2 gene mutation and 66 partners in the six to eight week period between genetic counselling/blood sampling and disclosure of the test result. Questionnaire and interview data are analysed. Associations are explored between levels of distress and (1) expected consequences of being identified as a mutation carrier, (2) personality traits, (3) sociodemographic variables, and (4) experiences related to HBOC. Mean pre-test anxiety and depression levels in women at risk of being a ...
European journal of human genetics : EJHG, Jan 18, 2015
This paper contains a joint ESHG/ASHG position document with recommendations regarding responsibl... more This paper contains a joint ESHG/ASHG position document with recommendations regarding responsible innovation in prenatal screening with non-invasive prenatal testing (NIPT). By virtue of its greater accuracy and safety with respect to prenatal screening for common autosomal aneuploidies, NIPT has the potential of helping the practice better achieve its aim of facilitating autonomous reproductive choices, provided that balanced pretest information and non-directive counseling are available as part of the screening offer. Depending on the health-care setting, different scenarios for NIPT-based screening for common autosomal aneuploidies are possible. The trade-offs involved in these scenarios should be assessed in light of the aim of screening, the balance of benefits and burdens for pregnant women and their partners and considerations of cost-effectiveness and justice. With improving screening technologies and decreasing costs of sequencing and analysis, it will become possible in t...
Dementia, 2009
Patients with frontotemporal dementia (FTD) need complete care in the final stages of the disease... more Patients with frontotemporal dementia (FTD) need complete care in the final stages of the disease. Some informal caregivers continue the in-home care whereas others institutionalize. This study identifies differences between in-home FTD patients and their caregivers (FTDH) and institutionalized FTD patients (FTDN) and their caregivers. Twelve in-home and 24 institutionalized FTD patients in the final stages of the disease, and
Dementia and Geriatric Cognitive Disorders, 2008
Background/Aims: The current study examined the change of caregiver burden and the development of... more Background/Aims: The current study examined the change of caregiver burden and the development of the quality of the partner relation in frontotemporal dementia (FTD). Methods: During a 2-year period, deterioration, behavioural problems, caregiver burden, general psychopathology, quality of life, social support, coping strategies and relationship quality were inspected in 63 FTD caregiver-care recipient dyads. Results: After 2 years patients reached
Oncologica / Vereniging van Oncologie Verpleegkundigen
Nederlands tijdschrift voor geneeskunde
Frontotemporal dementia (FTD) is a neurodegenerative disorder characterised by progressive behavi... more Frontotemporal dementia (FTD) is a neurodegenerative disorder characterised by progressive behavioural disturbance, aphasia and a decline in frontal cognitive functions. Frontotemporal atrophy on CT and MRI, and hypoperfusion of the frontal brain regions on single-photon emission computed tomography (SPECT), are characteristic findings. Neuropathological examination reveals deposition of abnormally phosphorylated tau protein in neurons and glial cells in a number of the sporadic and familial cases, while aspecific changes with neuronal loss, spongiosis and gliosis are found in the remaining cases. A familial form with an autosomal dominant pattern of inheritance is seen in 20% of FTD patients. Mutations in the tau gene have been identified in a number of families with deposition of abnormal tau protein in affected brain regions. Presymptomatic DNA testing is now available for relatives of patients with tau mutations, but must only be considered after extensive genetic counselling in...
The Medical journal of Australia, Jan 6, 2005
Objectives: To assess whether healthcare professionals correctly incorporate the relevance of a f... more Objectives: To assess whether healthcare professionals correctly incorporate the relevance of a favourable test outcome in a close relative when determining the level of risk for individuals at risk for Huntington's disease. Design and setting: Survey of clinical geneticists and genetic counsellors from 12 centres of clinical genetics (United Kingdom, 6; The Netherlands, 4; Italy, 1; Australia, 1) in May-June 2002. Participants were asked to assess risk of specific individuals in 10 pedigrees, three of which required use of Bayes' theorem. Participants: 71 clinical geneticists and 41 other healthcare professionals involved in genetic counselling. Main outcome measures: Proportion of respondents correctly assessing risk in the three target pedigrees; proportion of respondents who were confident of their estimate. Results: 50%-64% of respondents (for the three targets separately) did not include the favourable test information and incorrectly estimated the risks as being about equal to the prior risks; 77%-91% of these respondents were "sure" or "completely sure" that their estimations were correct. Twenty of the 112 respondents correctly estimated the risks for all three target pedigrees. Conclusions: Clinical geneticists and genetic counsellors frequently use prior risks in situations where Bayes' theorem should be applied, leading to overestimations of the MJA 2005; 182: 116-118 risk for an individual.
Brain, 2000
Several mutations in the amyloid precursor protein (APP) gene may lead to either Alzheimer&am... more Several mutations in the amyloid precursor protein (APP) gene may lead to either Alzheimer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease or cerebral haemorrhage due to congophilic amyloid angiopathy (CAA). A single family is known in which both types of pathology are expressed because of a missense mutation at codon 692 of the APP gene (APP692). Here we describe the clinical and pathological expression of APP692 in eight patients with the mutation. Furthermore, 21 first-degree relatives with an a priori risk of 50% of being a carrier were tested for the APP692 mutation and studied for presymptomatic signs by neurological examination, neuropsychological testing and brain MRI. Patients with APP692 presented with haemorrhage, dementia or both. The dementia in patients with the APP692 mutation was compatible with Alzheimer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease both clinically and neuropathologically. Of the 21 healthy relatives at 50% risk, five carried the APP692 mutation. The presymptomatic carriers showed a subtle, non-significant impairment of cognitive function compared with relatives without APP692. A significant increase in the number of periventricular and subcortical white matter lesions at young age was seen in presymptomatic carriers (mean age 26.4 years). The findings of this study suggest that a single (genetic) mechanism may underlie the pathology of Alzheimer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease and CAA. These diseases are manifested subclinically by white matter pathology. Further insight into the relationship between CAA and Alzheimer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease may provide clues about the aetiology of Alzheimer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease.
Psycho-Oncology, 2005
Since p16-Leiden presymptomatic testing for hereditary melanoma has become available in the Nethe... more Since p16-Leiden presymptomatic testing for hereditary melanoma has become available in the Netherlands, the benefits and risks of offering such testing are evaluated. The current paper investigated why the non-participants were reluctant to participate in genetic testing. Sixty six eligible individuals, who were knowledgeable about the test but had not participated in genetic testing by January 2003, completed a self-report questionnaire assessing motivation, anxiety, family dynamics, risk knowledge and causal attributions. Non-participants reported anxiety levels below clinical significance. A principal components analysis on reasons for non-participation distinguished two underlying motives: emotional and rational motivation. Rational motivation for non-participation was associated with more accurate risk knowledge, the inclination to preselect mutation carriers within the family and lower scores on anxiety. Emotional motivation for non-participation was associated with disease misperceptions, hesitation to communicate unfavourable test results within the family and higher scores on anxiety. Rational and emotional motivation for non-participation in the genetic test for hereditary melanoma was found. Emotionally motivated individuals may be reluctant to disseminate genetic risk information. Rationally motivated individuals were better informed than emotionally motivated individuals. It is suggested that a leaflet is added to the invitation letter to enhance informed decision-making about genetic testing.
Psycho-Oncology
Prospective studies regarding the psychosexual impact after different types of breast reconstruct... more Prospective studies regarding the psychosexual impact after different types of breast reconstruction (BR) are scarce. The impact of either implant or deep inferior epigastric artery perforator (DIEP) flap BR on body image and sexual relationship satisfaction was investigated in time. At baseline, 98 women opting for delayed implant or DIEP flap BR after mastectomy for breast cancer completed a survey. The majority was followed up at 6 months (96%) and 20 months (86%) postoperatively. Questionnaires included the body image scale, Dutch Relationship Questionnaire, Short Form - 36 Health Survey and the Impact of Event Scale. Mixed modeling analyses indicated that preoperative body image improved significantly after 20 months (p < 0.001), and there was no statistically significant difference between the two types of BR. A better body image was related to a better general mental health (p = 0.02), less cancer distress (p < 0.001) and a higher partner relationship satisfaction (p &l...
European Journal of Human Genetics, 2013
The Lancet
197 the treating physician. With the possible exception of tubal ligation, there is always a risk... more 197 the treating physician. With the possible exception of tubal ligation, there is always a risk, albeit low, of conception during treatment. The physician should then explain to the couple the risks and advantages of treatment, so that the partners agree to the use of additional and effective contraceptive measures. If conception does occur, abortion should be considered.
The Lancet
Marshall JB. Tuberculosis of the gastrointestinal tract and peritoneum. Am J Gastroenterol 1993; ... more Marshall JB. Tuberculosis of the gastrointestinal tract and peritoneum. Am J Gastroenterol 1993; 88: 989-99. 3 Puylaert JBCM, Vermeyden RJ, van der Werf SDJ, Doornbos L, Koumans RKJ. Incidence and sonographic diagnosis of bacterial ileocaecitis masquerading as appendicitis. Lancet 1989; ii: 84-86.
Nederlands tijdschrift voor geneeskunde
The American Journal of Human Genetics
Attitudes toward predictive testing programs, in individuals who choose not to undertake the test... more Attitudes toward predictive testing programs, in individuals who choose not to undertake the test (i.e., nonparticipants), may be influenced by fears of an unfavorable result. The reasons not to participate in predictive testing programs for Huntington disease (HD) were studied in members of the Dutch Huntington Association who were at 50% risk. They had completed the same baseline psychological questionnaires as had the participants in the Dutch DNA-testing program. The group of 34 nonparticipants was similar to the tested participants in the Dutch predictive testing program, with respect to average age (31.1 years), male:female ratio (1:2), the frequency of a stable relationship (70%), and level of education (67% had high school education or higher). Testing did not seem to be a realistic option for nonparticipants for improving their quality of life. In comparison with participants, nonparticipants had a significantly more pessimistic outlook on themselves and their futures. When...
Genetics in Medicine
To test the "false-reassurance hypothesis," which suggests that women who receive an un... more To test the "false-reassurance hypothesis," which suggests that women who receive an uninformative BRCA1/2 test result may incorrectly conclude that they no longer have an elevated risk, with possible harmful consequences for adherence to breast surveillance guidelines. A prospective questionnaire design was used to compare 183 women with an uninformative BRCA test result (94 affected and 89 unaffected) with 41 proven BRCA mutation-carriers and 49 true negatives before and after BRCA1/2 test disclosure. After DNA-test disclosure, test applicants differed from each other with regard to their perception of the likelihood of carrying a deleterious gene (P < 0.0001). The BRCA mutation carriers reported the highest perceived likelihood and the true negatives reported the lowest. Compared to the predisclosure measures, women who received an uninformative DNA test result reported a lower perceived risk after disclosure (P < 0.0001), suggesting a relatively high level of rea...
Journal of Medical Genetics, 1998
The first comparative study on predicting post-test distress (conceptualised by intrusion and avo... more The first comparative study on predicting post-test distress (conceptualised by intrusion and avoidance, measured with the Impact of Event Scale) after presymptomatic genetic testing for Huntington's disease (HD, n=25), cancer syndromes (familial adenomatous polyposis (FAP, n=23)), and hereditary breast and ovarian cancer (HBOC, n=10) is reported. The variables with the highest predictive potential of post-test distress are presented. Participants who
Journal of Medical Genetics, 1997
In a comparative study on the effects of predictive DNA testing for late onset disorders, pre-tes... more In a comparative study on the effects of predictive DNA testing for late onset disorders, pre-test psychological distress was assessed in people at risk for Huntington's disease (HD, n = 41), cerebral haemorrhage (HCHWA-D, n = 9), breast and ovarian cancer (HBOC, n = 24), and polyposis coli (FAP, n = 45). Partners, if available, also participated in the study.
Journal of plastic, reconstructive & aesthetic surgery : JPRAS, Jan 19, 2015
Journal of medical genetics, 1999
Presymptomatic DNA testing for autosomal dominant hereditary breast/ovarian cancer (HBOC) became ... more Presymptomatic DNA testing for autosomal dominant hereditary breast/ovarian cancer (HBOC) became an option after the identification of the BRCA1 and BRCA2 genes in 1994-1995. Healthy female mutation carriers have a high lifetime risk for breast cancer (56-87%) or ovarian cancer (10-60%) and may opt for intensive breast and ovary surveillance or prophylactic surgery (mastectomy/oophorectomy). We studied general and cancer related distress in 85 healthy women with a 25% or 50% risk of being carrier of a BRCA1/BRCA2 gene mutation and 66 partners in the six to eight week period between genetic counselling/blood sampling and disclosure of the test result. Questionnaire and interview data are analysed. Associations are explored between levels of distress and (1) expected consequences of being identified as a mutation carrier, (2) personality traits, (3) sociodemographic variables, and (4) experiences related to HBOC. Mean pre-test anxiety and depression levels in women at risk of being a ...
European journal of human genetics : EJHG, Jan 18, 2015
This paper contains a joint ESHG/ASHG position document with recommendations regarding responsibl... more This paper contains a joint ESHG/ASHG position document with recommendations regarding responsible innovation in prenatal screening with non-invasive prenatal testing (NIPT). By virtue of its greater accuracy and safety with respect to prenatal screening for common autosomal aneuploidies, NIPT has the potential of helping the practice better achieve its aim of facilitating autonomous reproductive choices, provided that balanced pretest information and non-directive counseling are available as part of the screening offer. Depending on the health-care setting, different scenarios for NIPT-based screening for common autosomal aneuploidies are possible. The trade-offs involved in these scenarios should be assessed in light of the aim of screening, the balance of benefits and burdens for pregnant women and their partners and considerations of cost-effectiveness and justice. With improving screening technologies and decreasing costs of sequencing and analysis, it will become possible in t...
Dementia, 2009
Patients with frontotemporal dementia (FTD) need complete care in the final stages of the disease... more Patients with frontotemporal dementia (FTD) need complete care in the final stages of the disease. Some informal caregivers continue the in-home care whereas others institutionalize. This study identifies differences between in-home FTD patients and their caregivers (FTDH) and institutionalized FTD patients (FTDN) and their caregivers. Twelve in-home and 24 institutionalized FTD patients in the final stages of the disease, and
Dementia and Geriatric Cognitive Disorders, 2008
Background/Aims: The current study examined the change of caregiver burden and the development of... more Background/Aims: The current study examined the change of caregiver burden and the development of the quality of the partner relation in frontotemporal dementia (FTD). Methods: During a 2-year period, deterioration, behavioural problems, caregiver burden, general psychopathology, quality of life, social support, coping strategies and relationship quality were inspected in 63 FTD caregiver-care recipient dyads. Results: After 2 years patients reached
Oncologica / Vereniging van Oncologie Verpleegkundigen
Nederlands tijdschrift voor geneeskunde
Frontotemporal dementia (FTD) is a neurodegenerative disorder characterised by progressive behavi... more Frontotemporal dementia (FTD) is a neurodegenerative disorder characterised by progressive behavioural disturbance, aphasia and a decline in frontal cognitive functions. Frontotemporal atrophy on CT and MRI, and hypoperfusion of the frontal brain regions on single-photon emission computed tomography (SPECT), are characteristic findings. Neuropathological examination reveals deposition of abnormally phosphorylated tau protein in neurons and glial cells in a number of the sporadic and familial cases, while aspecific changes with neuronal loss, spongiosis and gliosis are found in the remaining cases. A familial form with an autosomal dominant pattern of inheritance is seen in 20% of FTD patients. Mutations in the tau gene have been identified in a number of families with deposition of abnormal tau protein in affected brain regions. Presymptomatic DNA testing is now available for relatives of patients with tau mutations, but must only be considered after extensive genetic counselling in...
The Medical journal of Australia, Jan 6, 2005
Objectives: To assess whether healthcare professionals correctly incorporate the relevance of a f... more Objectives: To assess whether healthcare professionals correctly incorporate the relevance of a favourable test outcome in a close relative when determining the level of risk for individuals at risk for Huntington's disease. Design and setting: Survey of clinical geneticists and genetic counsellors from 12 centres of clinical genetics (United Kingdom, 6; The Netherlands, 4; Italy, 1; Australia, 1) in May-June 2002. Participants were asked to assess risk of specific individuals in 10 pedigrees, three of which required use of Bayes' theorem. Participants: 71 clinical geneticists and 41 other healthcare professionals involved in genetic counselling. Main outcome measures: Proportion of respondents correctly assessing risk in the three target pedigrees; proportion of respondents who were confident of their estimate. Results: 50%-64% of respondents (for the three targets separately) did not include the favourable test information and incorrectly estimated the risks as being about equal to the prior risks; 77%-91% of these respondents were "sure" or "completely sure" that their estimations were correct. Twenty of the 112 respondents correctly estimated the risks for all three target pedigrees. Conclusions: Clinical geneticists and genetic counsellors frequently use prior risks in situations where Bayes' theorem should be applied, leading to overestimations of the MJA 2005; 182: 116-118 risk for an individual.