Assessing biases of information contained in pedigrees for the classification of BRCA-genetic variants: a study arising from the ENIGMA analytical working group.

PURPOSE: One way of evaluating family history (FH) for classifying BRCA1/2 variants of uncertain clinical significance (VUS) is to assess the "BRCA-ness" of a pedigree by comparing it to reference populations. The aim of this study was to assess if prediction of BRCA pathogenic variant (mutation) status based on pedigree information differed due to changes in FH since intake, both in families with a pathogenic variant (BRCAm) and in families with wild-type (BRCAwt). PATIENTS AND METHODS: We compared the BRCA1/2 pathogenic variant detection probabilities between intake and most recent pedigree for BRCAm families (n = 64) and BRCAwt (n = 118) using the BRCAPRO software program. RESULTS: Follow-up time between intake and most recent pedigree was significantly longer (p < 0.001) in the BRCAm compared to the BRCAwt families. Among BRCAwt families, the probability to detect a pathogenic variant did not change over time. Conversely, among the BRCAm, this probability was significantly higher for most recent vs. intake pedigree (p = 0.006). CONCLUSION: Clinical scores change significantly over time for BRCAm families. This may be due to differences in follow-up, but also to differences in cancer risks from carrying a pathogenic variant in a highly penetrant gene. To reduce bias, models for VUS classification should incorporate FH collected at intake.

Colorectal cancer risk variants at 8q23.3 and 11q23.1 are associated with disease phenotype in APC mutation carriers.

Familial adenomatous polyposis (FAP) is a dominantly inherited syndrome caused by germline mutations in the APC gene and characterized by the development of multiple colorectal adenomas and a high risk of developing colorectal cancer (CRC). The severity of polyposis is correlated with the site of the APC mutation. However, there is also phenotypic variability within families with the same underlying APC mutation, suggesting that additional factors influence the severity of polyposis. Genome-wide association studies identified several single nucleotide polymorphisms (SNPs) that are associated with CRC. We assessed whether these SNPs are associated with polyp multiplicity in proven APC mutation carriers. Sixteen CRC-associated SNPs were analysed in a cohort of 419 APC germline mutation carriers from 182 families. Clinical data were retrieved from the Dutch Polyposis Registry. Allele frequencies of the SNPs were compared for patients with <100 colorectal adenomas versus patients with ≥100 adenomas, using generalized estimating equations with the APC genotype as a covariate. We found a trend of association of two of the tested SNPs with the ≥100 adenoma phenotype: the C alleles of rs16892766 at 8q23.3 (OR 1.71, 95 % CI 1.05-2.76, p = 0.03, dominant model) and rs3802842 at 11q23.1 (OR 1.51, 95 % CI 1.03-2.22, p = 0.04, dominant model). We identified two risk variants that are associated with a more severe phenotype in APC mutation carriers. These risk variants may partly explain the phenotypic variability in families with the same APC gene defect. Further studies with a larger sample size are recommended to evaluate and confirm the phenotypic effect of these SNPs in FAP.

BRCA1 and BRCA2 genetic testing-pitfalls and recommendations for managing variants of uncertain clinical significance.

BACKGROUND: Increasing use of BRCA1/2 testing for tailoring cancer treatment and extension of testing to tumour tissue for somatic mutation is moving BRCA1/2 mutation screening from a primarily prevention arena delivered by specialist genetic services into mainstream oncology practice. A considerable number of gene tests will identify rare variants where clinical significance cannot be inferred from sequence information alone. The proportion of variants of uncertain clinical significance (VUS) is likely to grow with lower thresholds for testing and laboratory providers with less experience of BRCA. Most VUS will not be associated with a high risk of cancer but a misinterpreted VUS has the potential to lead to mismanagement of both the patient and their relatives. DESIGN: Members of the Clinical Working Group of ENIGMA (Evidence-based Network for the Interpretation of Germline Mutant Alleles) global consortium (www.enigmaconsortium.org) observed wide variation in practices in reporting, disclosure and clinical management of patients with a VUS. Examples from current clinical practice are presented and discussed to illustrate potential pitfalls, explore factors contributing to misinterpretation, and propose approaches to improving clarity. RESULTS AND CONCLUSION: Clinicians, patients and their relatives would all benefit from an improved level of genetic literacy. Genetic laboratories working with clinical geneticists need to agree on a clinically clear and uniform format for reporting BRCA test results to non-geneticists. An international consortium of experts, collecting and integrating all available lines of evidence and classifying variants according to an internationally recognized system, will facilitate reclassification of variants for clinical use.

A white raven detected by imaging.

The purpose of this case report is to describe a rare case of a patient with a phaeochromocytoma with several cardiovascular complications, which can be attributed to the tumour. Detection of a phaeochromocytoma sometimes needs a 'Sherlock Holmes spirit' or simply time.

Breast cancer risk after salpingo-oophorectomy in healthy BRCA1/2 mutation carriers: revisiting the evidence for risk reduction.

BACKGROUND: Previous studies have reported a breast cancer (BC) risk reduction of approximately 50% after risk-reducing salpingo-oophorectomy (RRSO) in BRCA1/2 mutation carriers, but may have been subject to several types of bias. The purpose of this nationwide cohort study was to assess potential bias in the estimated BC risk reduction after RRSO. METHODS: We selected BRCA1/2 mutation carriers from an ongoing nationwide cohort study on Hereditary Breast and Ovarian Cancer in the Netherlands (HEBON). First, we replicated the analytical methods as previously applied in four major studies on BC risk after RRSO. Cox proportional hazards models were used to calculate hazard ratios and conditional logistic regression to calculate odds ratios. Secondly, we analyzed the data in a revised design in order to further minimize bias using an extended Cox model with RRSO as a time-dependent variable to calculate the hazard ratio. The most important differences between our approach and those of previous studies were the requirement of no history of cancer at the date of DNA diagnosis and the inclusion of person-time preceding RRSO. RESULTS: Applying the four previously described analytical methods and the data of 551 to 934 BRCA1/2 mutation carriers with a median follow-up of 2.7 to 4.6 years, the odds ratio was 0.61 (95% confidence interval [CI] = 0.35 to 1.08), and the hazard ratios were 0.36 (95% CI = 0.25 to 0.53), 0.62 (95% CI = 0.39 to 0.99), and 0.49 (95% CI = 0.33 to 0.71), being similar to earlier findings. For the revised analysis, we included 822 BRCA1/2 mutation carriers. After a median follow-up period of 3.2 years, we obtained a hazard ratio of 1.09 (95% CI = 0.67 to 1.77). CONCLUSION: In previous studies, BC risk reduction after RRSO in BRCA1/2 mutation carriers may have been overestimated because of bias. Using a design that maximally eliminated bias, we found no evidence for a protective effect.

Nonpolypoid colorectal neoplasms: a challenge in endoscopic surveillance of patients with Lynch syndrome.

BACKGROUND AND STUDY AIMS: Patients with Lynch syndrome may develop colorectal cancer (CRC), despite intensive colonoscopic surveillance. Nonpolypoid colorectal neoplasms might be a major contributor to the occurrence of these cancers. The aim of this case - control study was to compare the endoscopic appearance of colorectal neoplasms between patients with Lynch syndrome and control individuals at average risk for CRC. PATIENTS AND METHODS: The endoscopists at the Maastricht University Medical Center were first given training to ensure familiarity with the appearance and classification of nonpolypoid lesions. Patients with Lynch syndrome and patients at average risk for CRC who underwent elective colonoscopy at the Center were prospectively included. Nonpolypoid lesions were defined as lesions with a height of less than half the diameter, and advanced histology was defined as the presence of high grade dysplasia or early cancer. RESULTS: A total of 59 patients with Lynch syndrome (mean age 48.7 years, 47.5 % men) and 590 matched controls (mean age 50.2 years, 47.5 % men) were included. In patients with Lynch syndrome, adenomas were significantly more likely to be nonpolypoid than they were in controls: 43.3 % vs. 16.9 % (OR 3.60, 95 %CI 1.90 - 6.83; P < 0.001). This was particularly true for proximal adenomas: 58.1 % vs. 16.3 % (OR 6.93, 95 %CI 2.92 - 16.40; P < 0.001). Adenomas containing advanced histology were more often nonpolypoid in patients with Lynch syndrome than in controls (4/5, 80.0 % vs. 5/17, 29.4 %; P = 0.19). Serrated polyps were also more often nonpolypoid in patients with Lynch syndrome than in controls: 49.2 % vs. 20.4 % (OR 3.57, 95 %CI 1.91 - 6.68; P < 0.001). CONCLUSIONS: In patients with Lynch syndrome, colorectal neoplasms are more likely to have a nonpolypoid shape than those from average risk patients, especially in the proximal colon. These findings suggest that proficiency in recognition and endoscopic resection of nonpolypoid colorectal lesions are needed to ensure colonoscopic prevention against CRC in this high risk population.

Occult Breast Cancer due to Multiple Calcified Hamartomas in a Patient with Cowden Syndrome.

Cowden syndrome (CS) is an autosomal dominant disorder characterized by presence of multiple hamartomas, and other benign and malignant abnormalities of the breasts, skin, thyroid, endometrium, gastrointestinal tract, and central nervous system. Hamartomas are benign, developmentally disorganized tumors that can develop in any of the above mentioned organs. The presence of massive calcifications in the breasts in very young women is an indication to perform a breast MRI to exclude a neoplasm since, like in the current case report, presence of breast calcifications may obscure a neoplasm. Although fibrocystic disease and cooccurrence of fibrocystic disease and breast cancer are much more common than CS, the presence of massive calcifications in the breasts of very young women should elicit the possibility of an underlying genetic disease. Furthermore, breast cancer and macrocephaly are considered major criteria for the diagnosis of CS and the combination of both is enough to establish the clinical diagnosis of this entity. Fibrocystic disease of the breasts and multinodular goiter are minor criteria. Family history is also important for the diagnosis of (any) hereditary disease.

Is colorectal surveillance indicated in patients with PTEN mutations?

AIM: Patients with germline phosphatase and tensin homologue (PTEN) mutations develop hamartomatous lesions in several organs and are at increased risk of various malignancies. We assessed the lifetime risk of benign and malignant gastrointestinal lesions in patients with a proven PTEN mutation. METHOD: Data on gender, mutation, dates of birth, last contact, and diagnosis, location and type of gastrointestinal lesions were collected from nine countries. The lifetime risk of gastrointestinal lesions was calculated by Kaplan-Meier methods. RESULTS: A total of 156 patients (67 men, 43%) from 101 families with a PTEN mutation were included. Patients were born between 1928 and 2008. Benign gastrointestinal polyps were reported in 49 (31%) patients at a mean age of 38 years (range 18-62 years) and were most often hamartomas. Twenty-two (44%) patients had upper as well as lower gastrointestinal lesions, 14 (29%) had only colonic lesions and 13 (27%) had gastrointestinal lesions at unknown sites. The cumulative risk of developing benign gastrointestinal polyps was 70% at age 60. Four patients (two men) developed colorectal carcinoma at 53, 57, 59 and 62 years, respectively. The cumulative risk of developing colorectal carcinoma was 18% at age 60. Except for one carcinoid in the small intestine, no upper gastrointestinal cancers were observed. CONCLUSION: Benign gastrointestinal lesions are common in PTEN mutation carriers, and a three- to four-fold increased lifetime risk of colorectal cancer compared with the general population may exist. Colorectal screening of patients with germline PTEN mutations is recommended, starting at age 40 years.

Distress in partners of individuals diagnosed with or at high risk of developing tumors due to rare hereditary cancer syndromes.

OBJECTIVE: Li Fraumeni syndrome (LFS) and Von Hippel-Lindau disease (VHL) are two rare hereditary tumor syndromes, characterized by a high risk of developing multiple tumors at various sites and ages for which preventive and treatment options are limited. For partners, it may be difficult to deal with the on-going threat of tumors in both their spouse and children. Therefore, this study aims to evaluate the prevalence of and factors associated with psychological distress among partners of individuals with or at high risk of LFS or VHL. METHODS: As part of a nationwide, cross-sectional study, partners of individuals diagnosed with or at high risk of LFS or VHL were invited to complete a self-report questionnaire assessing distress, worries, and health-related quality of life. RESULTS: Fifty-five (58%) of those high-risk individuals with a partner consented to having their partner approached for the study. In total, 50 partners (91%) completed the questionnaire, of whom 28% reported clinically relevant levels of syndrome-related distress. Levels of distress and worries of the partners and their high-risk spouse were significantly correlated. Younger age and a lack of social support were also associated significantly with heightened levels of distress and worries. The majority of partners (76%) believed that professional psychosocial support should be routinely offered to them. CONCLUSIONS: Approximately one-quarter of the partners exhibit clinically relevant levels of distress that warrant psychological support. The distress levels of the 'patient' could potentially be used to identify partners at risk of developing clinically relevant levels of distress.

Regular surveillance for Li-Fraumeni Syndrome: advice, adherence and perceived benefits.

Li Fraumeni Syndrome (LFS) is a hereditary cancer syndrome characterized by a high risk of developing various types of cancer from birth through late adulthood. Clinical benefits of surveillance for LFS are limited. The aim of this study is to investigate which advice for regular surveillance, if any, is given to high risk LFS individuals, adherence to that advice, and any psychological gain or burden derived from surveillance. Fifty-five high risk individuals (proven carriers and those at 50% risk) from families with a p53 germline mutation were invited to participate, of whom 82% completed a self-report questionnaire assessing advice for regular surveillance, compliance, perceived benefits and barriers of screening and LFS-related distress (IES) and worries (CWS). In total, 71% of the high risk family members received advice to undergo regular surveillance for LFS. The majority (78%) reported adherence with the recommended advice. All high risk women aged 25 or older reported having been advised to undergo annual breast cancer surveillance (n = 11), of whom 64% (n = 7) in specific received advice to undergo a mammography. Seventy-eight percent of respondents indicated having received tailored surveillance advice based on family cancer history. The large majority of respondents believed in the value of surveillance to detect tumors at an early stage (90%) and reported that it gave them a sense of control (84%) and security (70%). Despite its limited clinical benefits, the majority of high risk LFS family are advised to undergo, and are adherent to, and report psychological benefit from, regular surveillance programs.

Psychosocial impact of Von Hippel-Lindau disease: levels and sources of distress.

Von Hippel-Lindau disease (VHL) is a hereditary tumor susceptibility syndrome, characterized by an increased risk of developing multiple benign and malignant tumors at various sites and ages with limited preventive options. This study evaluates the prevalence of distress among VHL family members and factors associated significantly with such distress. Forty-eight families with a VHL mutation were identified via the nine family cancer clinics in the Netherlands. In total, 171 family members (carriers, 50% at-risk, non-carriers) were approached, of whom 123 (72%) completed a self-report questionnaire. Approximately 40% of the VHL family members reported clinically relevant levels of distress, approaching 50% among the carriers and, possibly even more striking, 36% among the non-carriers. Having lost a first degree relative due to VHL during adolescence (OR 11.2; 95% CI 1.4-86.9) was related significantly to heightened levels of distress. Approximately, only one-third of those who reported heightened levels of distress had received professional psychosocial support. A substantial percentage of family members experience clinically relevant levels of distress. We would recommend the introduction of a procedure for screening for distress in this vulnerable population. Special attention should be paid to those individuals who have lost a close relative due to VHL during adolescence.

Efficiency of BRCAPRO and Myriad II mutation probability thresholds versus cancer history criteria alone for BRCA1/2 mutation detection.

Considerable differences exist amongst countries in the mutation probability methods and thresholds used to select patients for BRCA1/2 genetic screening. In order to assess the added value of mutation probability methods, we have retrospectively calculated the BRCAPRO and Myriad II probabilities in 306 probands who had previously been selected for DNA-analysis according to criteria based on familial history of cancer. DNA-analysis identified 52 mutations (16.9%) and 11 unclassified variants (UVs, 3.6%). Compared to cancer history, a threshold > or = 10% with BRCAPRO or with Myriad II excluded about 40% of the patients from analysis, including four with a mutation and probabilities <10% with both programs. All four probands had a BRCA2 mutation. BRCAPRO and Myriad II showed similar specificity at 10% threshold, overall BRCAPRO was more sensitive than Myriad II for the detection of mutations. Only two of the probands with an UV had probabilities >20% with BRCAPRO and Myriad II. In summary, BRCAPRO and Myriad II are more efficient than cancer history alone to exclude patients without a mutation. BRCAPRO performs better for the detection of BRCA1 mutations than of BRCA2 mutations. The Myriad II scores provided no additional information than the BRCAPRO scores alone for the detection of patients with a mutation. The use of thresholds excluded from analysis the majority of patients carrying an UV.

Multiplicity in polyp count and extracolonic manifestations in 40 Dutch patients with MYH associated polyposis coli (MAP).

OBJECTIVE: To investigate the contribution of MYH associated polyposis coli (MAP) among polyposis families in the Netherlands, and the prevalence of colonic and extracolonic manifestations in MAP patients. METHODS: 170 patients with polyposis coli, who previously tested negative for APC mutations, were screened by denaturing gradient gel electrophoresis and direct sequencing to identify MYH germline mutations. RESULTS: Homozygous and compound heterozygous MYH mutations were identified in 40 patients (24%). No difference was found in the percentage of biallelic mutation carriers between patients with 10-99 polyps or 100-1000 polyps (29% in both groups). Colorectal cancer was found in 26 of the 40 patients with MAP (65%) within the age range 21 to 67 years (median 45). Complete endoscopic reports were available for 16 MAP patients and revealed five cases with gastro-duodenal polyps (31%), one of whom also presented with a duodenal carcinoma. Breast cancer occurred in 18% of female MAP patients, significantly more than expected from national statistics (standardised morbidity ratio = 3.75). CONCLUSIONS: Polyp numbers in MAP patients were equally associated with the attenuated and classical polyposis coli phenotypes. Two thirds of the MAP patients had colorectal cancer, 95% of whom were older than 35 years, and one third of a subset of patients had upper gastrointestinal lesions. Endoscopic screening of the whole intestine should be carried out every two years for all MAP patients, starting from age 25-30 years. The frequent occurrence of additional extraintestinal manifestations, such as breast cancer among female MAP patients, should be thoroughly investigated.

Cancer risks in BRCA2 families: estimates for sites other than breast and ovary.

BACKGROUND: In BRCA2 mutation carriers, increased risks have been reported for several cancer sites besides breast and ovary. As most of the families included in earlier reports were selected on the basis of multiple breast/ovarian cancer cases, it is possible that risk estimates may differ in mutation carriers with a less striking family history. METHODS: In the Netherlands, 139 BRCA2 families with 66 different pathogenic mutations were included in a nationwide study. To avoid testing bias, we chose not to estimate risk in typed carriers, but rather in male and female family members with a 50% prior probability of being a carrier (n = 1811). The relative risk (RR) for each cancer site with the exception of breast and ovarian cancer was determined by comparing observed numbers with those expected, based on Dutch cancer incidence rates. RESULTS: We observed an excess risk for four cancer sites: pancreas (RR 5.9; 95% confidence interval (CI) 3.2 to 10.0), prostate (2.5; 1.6 to 3.8), bone (14.4; 2.9 to 42.1) and pharynx (7.3; 2.0 to 18.6). A small increase was observed for cancer of the digestive tract (1.5; 1.1 to 1.9). Histological verification was available for 46% of the tumours. Nearly all increased risks reached statistical significance for men only. Cancer risks tended to be higher for people before the age of 65 years. Moreover, families with mutations outside the previously defined ovarian cancer cluster region tended to have a higher cancer risk. CONCLUSIONS: We found that BRCA2 carriers are at increased risk for cancers of the prostate and pancreas, and possibly bone and pharynx. Larger databases with extended follow up are needed to provide insight into mutation specific risks of selected carriers in BRCA2 families.

The -148 C/T fibrinogen gene polymorphism and fibrinogen levels in ischaemic stroke: a case-control study.

BACKGROUND: To determine whether -148 C/T fibrinogen gene promoter polymorphism increases stroke risk by modifying the fibrinogen level. DESIGN: A case-control study of patients with first ever ischaemic stroke, confirmed by computed tomography. METHODS: Venous blood samples were collected for fibrinogen and routine coagulation tests one week after the stroke, and after three months in about half the patients. Population controls were age and sex matched. -148 C/T fibrinogen polymorphism was determined by polymerase chain reaction followed by digestion with restriction enzymes HindIII/AluI. RESULTS: There were 124 patients and 125 controls, mean age 56 years (range 18 to 75); 34 patients (27%) and 41 controls (33%) were heterozygous for -148 C/T fibrinogen polymorphism; six patients (5%) and five controls (4%) had the T/T genotype. The odds ratio of ischaemic stroke associated with CC homozygotes v T carriers was 0.8 (95% confidence interval, 0.5 to 1.4). Relative risk for ischaemic stroke associated with fibrinogen levels in the highest quartile was 3.9 (1.9 to 8.4) at one week, decreasing to 1.4 (0.6 to 3.3) at three months. CONCLUSIONS: -148 C/T fibrinogen gene polymorphism was not a strong risk factor for ischaemic stroke. High fibrinogen levels early after acute stroke probably represent an acute phase response.

Hyponatraemic coma induced by desmopressin and ibuprofen in a woman with von Willebrand's disease.

A middle-aged woman was admitted to the hospital after being found unconscious at home. A brain CT scan excluded an intracranial bleed or other focal abnormality. Laboratory analysis showed hyponatraemia (sodium: 121 mmol L(-1)) and a low plasma osmolality, with normal sodium excretion and urine osmolality. A diagnosis of hyponatraemic coma was made. The patient was treated with water restriction; 24 h later the sodium was 135 mmol L(-1) and the patient was neurologically fully recovered. The patient, who suffered from von Willebrand's disease, had received desmopressin and ibuprofen for analgesia 2 days before after a dental intervention. She had received desmopressin several times in the past without any complications. A few patients treated with desmopressin for coagulation abnormalities have been reported to develop water intoxication and severe hyponatraemia resulting in seizures and coma. By inhibiting prostaglandin synthesis, non-steroid anti-inflammatory agents (NSAIDs) potentiate the effect of water reabsorption in the renal tubules of vasopressin, therefore enhancing water retention. Desmopressin and NSAIDs should not be used in combination in patients with bleeding disorders, but it is often followed in clinical practice. In addition, this is probably not an unusual situation in patients treated with desmopressin for other 'non-haemorrhagic' indications. This report emphasizes the need for practitioners to be aware of this rare but severe complication.

Levels of vitamin K-dependent procoagulant and anticoagulant proteins in over-anticoagulated patients.

Coumarin anticoagulants impair the biological activity of the vitamin K-dependent procoagulant and anticoagulant proteins. There are no reports that focus on the levels of these proteins in over-anticoagulated patients. Therefore, we determined the levels of factor II, factor VII, factor IX and factor X, protein C and protein S in 25 randomly selected over-anticoagulated patients (International Normalized Ratio >/= 6.0) and in 25 matched, therapeutically anticoagulated patients with an International Normalized Ratio within the therapeutic zone. Furthermore, to study a possible effect of the cause of over-anticoagulation, coagulant levels were compared between 16 over-anticoagulated patients with fever in the preceding 2 weeks and 24 over-anticoagulated patients with stable congestive heart failure. The pattern of procoagulant level reductions in the three groups of over-anticoagulated patients was largely the same as in therapeutically anticoagulated patients: factor X was the lowest and factor IX the highest. The difference was that, in over-anticoagulated patients, factor VII was relatively low among the procoagulant factors compared with therapeutically anticoagulated patients. Protein C was lower than protein S in over-anticoagulated patients with congestive heart failure, but was similar to protein S in the other study groups. In over-anticoagulated patients with fever, the vitamin K-dependent coagulation proteins except factor X were significantly lower than in over-anticoagulated patients with congestive heart failure, especially factor VII and protein S.

Elevated prothrombin is a risk factor for cerebral arterial ischemia in young adults.

The prevalence of elevated prothrombin (PT) in the absence of the G20210A mutation has not been studied in patients with cerebral ischemia. We carried out a case-control study of PT G20210A and PT activity in 49 adult patients aged 45 years or less, with TIA or ischemic stroke without cardiac embolism or large vessel disease, and 87 controls from a group of blood donors. Five patients were heterozygous for PT 20210A (OR=2.3, 95% CI: 0.6-8.0). Even after exclusion of individuals with the PT gene variant, the PT activity was significantly higher in patients than in controls (1.11 vs. 0.97, P=0.0003). The relative risk of cerebral ischemia in patients within the fourth quartile of PT activity (1.10 U/ml or higher), was 3.2 fold (95% CI: 1.03-9.96), than in patients whose level of PT activity was in the second or third quartile. We conclude that, although PT 20210A may be a weak risk factor for TIA and ischemic stroke in young patients, increased PT activity, which is more frequent than the mutation, appears to be more strongly related to cerebral ischemia.

[From gene to disease; from mutations in the Von Willebrand factor gene to hemorrhagic diathesis and thrombocytopenia]. / Van gen naar ziekte; van mutaties in het Von Willebrand-factorgen naar hemorragische diathese en trombocytopenie.

The broad spectrum of both clinical presentation and severity of bleeding complications observed in Von Willebrand's disease is the result of a high number of mutations. Most are clustered in specific functional domains, leading to quantitative (types 1 and 3) or qualitative (types 2: A, B, M and N or Normandy) defects in the Von Willebrand factor (VWF) protein. Unlike all the other subtypes, type 2B is the result of a 'gain of function' phenotype characterised by an enhanced binding affinity of the VWF protein to the glycoprotein (Gp) Ib complex of platelets, which causes the platelets to disappear from the circulation, resulting in thrombocytopenia. The thrombocytopenia can be triggered by stress or desmopressin, among other causes, and therefore the latter is contraindicated. Type 2B is characterised in vitro by enhanced platelet agglutination with ristocetin. All 2B mutations are located in exon 28, in a small region encoding the Gp-Ib binding site within the A1 domain of VWF. These mutations inactivate a regulatory function of the A1 domain which facilitates Gp-Ib binding.

[Intermittent thrombocytopenia as a manifestation of Von Willebrand's disease]. / Intermitterende trombocytopenie als uiting van de ziekte van Von Willebrand.

A 38-year-old man with Von Willebrand's disease type 2 came to us for treatment advice in relation to a trip abroad, and also a 53-year-old woman with bleeding treated as idiopathic thrombocytopenic purpura (ITP). In the man, a trial dose of desmopressin led to severe thrombopenia, and in the woman, treatments, such as splenectomy and prednisone in the past, had been ineffective. In both patients further investigations led to the diagnosis 'Von Willebrand-disease type 2B'. Despite the fact that Von Willebrand's disease type 2B has distinctive laboratory characteristics, such as thrombocytopenia, a positive Ristocetin Induced Platelet Agglutination (RIPA) test at a low ristocetin concentration, and an abnormal multimer pattern, some cases have incomplete or atypical presentations which can be misleading for the diagnosis. A wrong diagnosis can lead to ineffective and potentially dangerous therapeutic interventions. Molecular genetic analysis of type 2B mutations is simple and can help in making the correct diagnosis in cases of familial thrombocytopenia or for a further characterisation of Von Willebrand type 2.