Duration of rectal colonization with extended-spectrum beta-lactamase-producing Escherichia coli: results of an open, dynamic cohort study in Dutch nursing home residents (2013–2019)

Background

In 2016, a study in a Dutch nursing home showed prolonged colonization duration of extended-spectrum β-lactamase-producing (ESBL)-ST131 compared to ESBL-non-ST131. In this study, we assessed the duration of rectal ESBL-producing E. coli (ESBL-EC) colonization in residents in the same nursing home for an extended period of six years. We aimed to estimate the influence of a possible bias when follow up is started during an outbreak.

Methods

Between 2013 and 2019, repetitive point prevalence surveys were performed by culturing rectal or faecal swabs from all residents. Kaplan–Meier survival analysis was performed to calculate the median time to clearance of ESBL-EC with a log-rank analysis to test for differences between ESBL-ST131 and ESBL-non-ST131.

Results

The study showed a median time to clearance of 13.0 months (95% CI 0.0–27.9) for ESBL-ST131 compared to 11.2 months (95% CI 4.8–17.6) for ESBL-non-ST131 (p = 0.044). In the subgroup analysis of residents who were ESBL-EC positive in their first survey, the median time to clearance for ST131 was 59.7 months (95% CI 23.7–95.6) compared to 16.2 months (95% CI 2.1–30.4) for ESBL-non-ST131 (p = 0.036). In the subgroup analysis of residents who acquired ESBL-EC, the median time to clearance for ST131 was 7.2 months (95% CI 2.1–12.2) compared to 7.9 months (95% CI 0.0–18.3) for ESBL-non-ST131 (p = 0.718). The median time to clearance in the ESBL-ST131 group was significantly longer in residents who were ESBL-ST131 colonised upon entering the study than in residents who acquired ESBL-ST131 during the study (p = 0.001).

Conclusion

A prolonged colonization with ESBL-ST131 was only found in the subgroup who was ESBL-EC positive upon entering the study. The prolonged duration with ESBL-ST131 in the previous study was probably biased by factors that occured during (the start of) the outbreak.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13756-022-01132-9.

Biallelic POC1A variants cause syndromic severe insulin resistance with muscle cramps

OBJECTIVE

To describe clinical, laboratory, and genetic characteristics of three unrelated cases from Chile, Portugal, and Saudi Arabia with severe insulin resistance, SOFT syndrome, and biallelic pathogenic POC1A variants.

DESIGN

Observational study.

METHODS

Probands' phenotypes, including short stature, dysmorphism, and insulin resistance, were compared with previous reports.

RESULTS

Cases 1 (female) and 3 (male) were homozygous for known pathogenic POC1A variants: c.649C>T, p.(Arg217Trp) and c.241C>T, p.(Arg81*), respectively. Case 2 (male) was compound heterozygous for p.(Arg217Trp) variant and the rare missense variant c.370G>A, p.(Asp124Asn). All three cases exhibited severe insulin resistance, acanthosis nigricans, elevated serum triglycerides and decreased HDL, and fatty liver, resembling three previously reported cases. All three also reported severe muscle cramps. Aggregate analysis of the six known cases with biallelic POC1A variants and insulin resistance showed decreased birth weight and length mean (s.d.): -2.8 (0.9) and -3.7 (0.9) SDS, respectively), severe short stature mean (s.d.) height: -4.9 (1.7) SDS) and moderate microcephaly (mean occipitofrontal circumference -3.0 (range: -4.7 to -1.2)). These findings were similar to those reported for patients with SOFT syndrome without insulin resistance. Muscle biopsy in Case 3 showed features of muscle involvement secondary to a neuropathic process.

CONCLUSIONS

Patients with SOFT syndrome can develop severe dyslipidaemic insulin resistance, independent of the exonic position of the POC1A variant. They also can develop severe muscle cramps. After diagnosis, patients should be regularly screened for insulin resistance and muscle complaints.

Variants in NGLY1 lead to intellectual disability, myoclonus epilepsy, sensorimotor axonal polyneuropathy and mitochondrial dysfunction

NGLY1 encodes the enzyme N‐glycanase that is involved in the degradation of glycoproteins as part of the endoplasmatic reticulum‐associated degradation pathway. Variants in this gene have been described to cause a multisystem disease characterized by neuromotor impairment, neuropathy, intellectual disability, and dysmorphic features. Here, we describe four patients with pathogenic variants in NGLY1. As the clinical features and laboratory results of the patients suggested a multisystem mitochondrial disease, a muscle biopsy had been performed. Biochemical analysis in muscle showed a strongly reduced ATP production rate in all patients, while individual OXPHOS enzyme activities varied from normal to reduced. No causative variants in any mitochondrial disease genes were found using mtDNA analysis and whole exome sequencing. In all four patients, variants in NGLY1 were identified, including two unreported variants (c.849T>G (p.(Cys283Trp)) and c.1067A>G (p.(Glu356Gly)). Western blot analysis of N‐glycanase in muscle and fibroblasts showed a complete absence of N‐glycanase. One patient showed a decreased basal and maximal oxygen consumption rates in fibroblasts. Mitochondrial morphofunction fibroblast analysis showed patient specific differences when compared to control cell lines. In conclusion, variants in NGLY1 affect mitochondrial energy metabolism which in turn might contribute to the clinical disease course.

Variable workup calls for guideline development for type 2A hereditary haemochromatosis

BACKGROUND

Type 2A hereditary haemochromatosis (type 2A HH) is a rare iron-loading disorder caused by mutations in the HFE2 gene, which encodes the HJV protein. We present characteristics, treatment and follow-up of subjects diagnosed with type 2A HH in the Netherlands to increase awareness of the disease and its treatment, and to define knowledge gaps.

METHODS

We collected clinical, biochemical and genetic data from seven patients (two female; five probands) from six families genetically diagnosed with type 2A HH at the Expertise Center for Iron Disorders, Radboud University Medical Centre between 2006 and 2016.

RESULTS

The five probands presented with heterogeneous complaints between the ages of 19 and 39. One of two patients with delayed clinical diagnosis developed hypogonadism and Y. enterocolitica sepsis. Diagnostic workup and follow-up varied. When assessed, elevated transferrin saturation (79-98%), ferritin (1400-6200 µg/l) and severely elevated liver iron levels were found, and in all subjects, phlebotomies were initiated. One subject was switched to erythrocytapheresis. Target ferritin levels varied. Despite long-term iron depletion, two subjects developed clinical complications. Sanger sequencing revealed two pathogenic HFE2 variants (homozygous or compound heterozygous) for the five families of Dutch descent and one new pathogenic variant in the family of non-Dutch descent.

CONCLUSION

Three genetic variants caused type 2A HH in six families. Clinical diagnosis was delayed in two subjects. We observed variance in presentation, workup, follow-up and treatment. We found new complications in long-term iron-depleted patients. We recommend research and guidelines for optimal workup, follow-up and treatment of type 2A HH.

Prolonged colonisation with Escherichia coli O25:ST131 versus other extended-spectrum beta-lactamase-producing E. coli in a long-term care facility with high endemic level of rectal colonisation, the Netherlands, 2013 to 2014

The extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli clone ST131 (ESBL-ST131) has spread in healthcare settings worldwide. The reasons for its successful spread are unknown, but might include more effective transmission and/or longer persistence. We evaluated the colonisation dynamics of ESBL-producing E. coli (ESBL-EC), including ESBL-ST131, in a long-term care facility (LTCF) with an unusually high prevalence of rectal ESBL-EC colonisation. During a 14-month period, rectal or faecal samples were obtained from 296 residents during six repetitive prevalence surveys, using ESBL-selective culture. Transmission rates, reproduction numbers, and durations of colonisation were compared for ESBL-ST131 vs other ESBL-EC. Furthermore, the likely time required for ESBL-ST131 to disappear from the LTCF was estimated. Over time, the endemic level of ESBL-ST131 remained elevated whereas other ESBL-EC returned to low-level prevalence, despite comparable transmission rates. Survival analysis showed a half-life of 13 months for ESBL-ST131 carriage, vs two to three months for other ESBL-EC (p < 0.001). Per-admission reproduction numbers were 0.66 for ESBL-ST131 vs 0.56 for other ESBL-EC, predicting a mean time of three to four years for ESBL-ST131 to disappear from the LTCF under current conditions. Transmission rates were comparable for ESBL-ST131 vs other ESBL-EC. Prolonged rectal carriage explained the persistence of ESBL-ST131 in the LTCF.

Missense-depleted regions in population exomes implicate ras superfamily nucleotide-binding protein alteration in patients with brain malformation

Genomic sequence interpretation can miss clinically relevant missense variants for several reasons. Rare missense variants are numerous in the exome and difficult to prioritise. Affected genes may also not have existing disease association. To improve variant prioritisation, we leverage population exome data to identify intragenic missense-depleted regions (MDRs) genome-wide that may be important in disease. We then use missense depletion analyses to help prioritise undiagnosed disease exome variants. We demonstrate application of this strategy to identify a novel gene association for human brain malformation. We identified de novo missense variants that affect the GDP/GTP-binding site of ARF1 in three unrelated patients. Corresponding functional analysis suggests ARF1 GDP/GTP-activation is affected by the specific missense mutations associated with heterotopia. These findings expand the genetic pathway underpinning neurologic disease that classically includes FLNA. ARF1 along with ARFGEF2 add further evidence implicating ARF/GEFs in the brain. Using functional ontology, top MDR-containing genes were highly enriched for nucleotide-binding function, suggesting these may be candidates for human disease. Routine consideration of MDR in the interpretation of exome data for rare diseases may help identify strong genetic factors for many severe conditions, infertility/reduction in reproductive capability, and embryonic conditions contributing to preterm loss.

Measuring the quality of infection control in Dutch nursing homes using a standardized method; the Infection prevention RIsk Scan (IRIS)

Background

We developed a standardised method to assess the quality of infection control in Dutch Nursing Home (NH), based on a cross-sectional survey that visualises the results. The method was called the Infection control RIsk Infection Scan (IRIS). We tested the applicability of this new tool in a multicentre surveillance executed June and July 2012.

Methods

The IRIS includes two patient outcome-variables, i.e. the prevalence of healthcare associated infections (HAI) and rectal carriage of Extended-Spectrum Beta-Lactamase (ESBL) producing Enterobacteriaceae (ESBL-E); two patient-related risk factors, i.e. use of medical devices, and antimicrobial therapy; and three ward-related risk factors, i.e. environmental contamination, availability of local guidelines, and shortcomings in infection prevention preconditions. Results were categorised as low-, intermediate- and high risk, presented in an easy-to-read graphic risk spider-plot. This plot was given as feedback to management and healthcare workers of the NH.

Results

Large differences were found among most the variables in the different NH. Common shortcomings were the availability of infection control guidelines and the level of environmental cleaning. Most striking differences were observed in the prevalence of ESBL carriage, ranged from zero to 20.6% (p < 0.001).

Conclusions

The IRIS provided a rapid and easy to understand assessment of the infection control situation of the participating NH. The results can be used to improve the quality of infection control based on the specific needs of a NH but needs further validation in future studies. Repeated measurement can determine the effectiveness of the interventions. This makes the IRIS a useful tool for quality systems.

Thirteen new patients with guanidinoacetate methyltransferase deficiency and functional characterization of nineteen novel missense variants in the GAMT gene

Guanidinoacetate methyltransferase deficiency (GAMT-D) is an autosomal recessively inherited disorder of creatine biosynthesis. Creatine deficiency on cranial proton magnetic resonance spectroscopy, and elevated guanidinoacetate levels in body fluids are the biomarkers of GAMT-D. In 74 patients, 50 different mutations in the GAMT gene have been identified with missense variants being the most common. Clinical and biochemical features of the patients with missense variants were obtained from their physicians using a questionnaire. In 20 patients, 17 missense variants, 25% had a severe, 55% a moderate, and 20% a mild phenotype. The effect of these variants on GAMT enzyme activity was overexpressed using primary GAMT-D fibroblasts: 17 variants retained no significant activity and are therefore considered pathogenic. Two additional variants, c.22C>A (p.Pro8Thr) and c.79T>C (p.Tyr27His) (the latter detected in control cohorts) are in fact not pathogenic as these alleles restored GAMT enzyme activity, although both were predicted to be possibly damaging by in silico analysis. We report 13 new patients with GAMT-D, six novel mutations and functional analysis of 19 missense variants, all being included in our public LOVD database. Our functional assay is important for the confirmation of the pathogenicity of identified missense variants in the GAMT gene.

Implementation of a bundle of care to reduce surgical site infections in patients undergoing vascular surgery

Background

Surgical site infections (SSI’s) are associated with severe morbidity, mortality and increased health care costs in vascular surgery.

Objective

To implement a bundle of care in vascular surgery and measure the effects on the overall and deep-SSI’s rates.

Design

Prospective, quasi-experimental, cohort study.

Methods

A prospective surveillance for SSI’s after vascular surgery was performed in the Amphia hospital in Breda, from 2009 through 2011. A bundle developed by the Dutch hospital patient safety program (DHPSP) was introduced in 2009. The elements of the bundle were (1) perioperative normothermia, (2) hair removal before surgery, (3) the use of perioperative antibiotic prophylaxis and (4) discipline in the operating room. Bundle compliance was measured every 3 months in a random sample of surgical procedures and this was used for feedback.

Results

Bundle compliance improved significantly from an average of 10% in 2009 to 60% in 2011. In total, 720 vascular procedures were performed during the study period and 75 (10.4%) SSI were observed. Deep SSI occurred in 25 (3.5%) patients. Patients with SSI’s (28,5±29.3 vs 10.8±11.3, p<0.001) and deep-SSI’s (48.3±39.4 vs 11.4±11.8, p<0.001) had a significantly longer length of hospital stay after surgery than patients without an infection. A significantly higher mortality was observed in patients who developed a deep SSI (Adjusted OR: 2.96, 95% confidence interval 1.32–6.63). Multivariate analysis showed a significant and independent decrease of the SSI-rate over time that paralleled the introduction of the bundle. The SSI-rate was 51% lower in 2011 compared to 2009.

Conclusion

The implementation of the bundle was associated with improved compliance over time and a 51% reduction of the SSI-rate in vascular procedures. The bundle did not require expensive or potentially harmful interventions and is therefore an important tool to improve patient safety and reduce SSI’s in patients undergoing vascular surgery.

Reduction of surgical site infections after implementation of a bundle of care

Background

Surgical Site Infections (SSI) are relatively frequent complications after colorectal surgery and are associated with substantial morbidity and mortality.

Objective

Implementing a bundle of care and measuring the effects on the SSI rate.

Design

Prospective quasi experimental cohort study.

Methods

A prospective surveillance for SSI after colorectal surgery was performed in the Amphia Hospital, Breda, from January 1, 2008 until January 1, 2012. As part of a National patient safety initiative, a bundle of care consisting of 4 elements covering the surgical process was introduced in 2009. The elements of the bundle were perioperative antibiotic prophylaxis, hair removal before surgery, perioperative normothermia and discipline in the operating room. Bundle compliance was measured every 3 months in a random sample of surgical procedures.

Results

Bundle compliance improved significantly from an average of 10% in 2009 to 60% in 2011. 1537 colorectal procedures were performed during the study period and 300 SSI (19.5%) occurred. SSI were associated with a prolonged length of stay (mean additional length of stay 18 days) and a significantly higher 6 months mortality (Adjusted OR: 2.71, 95% confidence interval 1.76–4.18). Logistic regression showed a significant decrease of the SSI rate that paralleled the introduction of the bundle. The adjusted Odds ratio of the SSI rate was 36% lower in 2011 compared to 2008.

Conclusion

The implementation of the bundle was associated with improved compliance over time and a 36% reduction of the SSI rate after adjustment for confounders. This makes the bundle an important tool to improve patient safety.

Outbreak of methicillin-resistant Staphylococcus aureus ST398 in a Dutch nursing home

We describe an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) ST398 in a nursing home in the Netherlands. Seven residents and 4 healthcare workers were identified with MRSA ST398, but 2 of the healthcare workers carried other strains. This study demonstrates that MRSA ST398 can spread in nursing homes.

Identification of 34 novel and 56 known FOXL2 mutations in patients with Blepharophimosis syndrome

Blepharophimosis syndrome (BPES) is caused by loss-of-function mutations in the single-exon forkhead transcription factor gene FOXL2 and by genomic rearrangements of the FOXL2 locus. Here, we focus on 92 new intragenic FOXL2 mutations, 34 of which are novel. Specifically, we found 10 nonsense mutations (11%), 13 missense mutations (14%), 40 deletions or insertions leading to a frameshift (43%), and 29 in-frame changes (32%), of which 28 (30%) lead to a polyalanine expansion. This study confirms the existence of two previously described mutational hotspots. Moreover, we gained novel insights in genotype-phenotype correlations, emphasizing the need to interpret genotype-phenotype correlations individually and always in the context of further clinical observations.

Familial CHARGE syndrome and the CHD7 gene: a recurrent missense mutation, intrafamilial recurrence and variability

CHARGE syndrome is an autosomal dominant condition that is caused by mutations in the CHD7 gene. Few familial cases of this syndrome have been reported and these were characterized by a wide clinical variability. We here report on five CHD7 mutation positive families and comment on their clinical features. We observed somatic and germline mosaicism as well as parent-to-child transmission of non-mosaic CHD7 mutations as causes of familial CHARGE syndrome. In one family with two affected sibs a somatic mutation was identified in lymphocytes of a clinically unaffected parent (2520G > A in exon 8). This is the second report of somatic CHD7 mosaicism in an unaffected parent. In two further families with affected siblings, we could not detect the mutation in parental lymphocytes suggesting germline mosaicism. The previously reported clinical variability was strikingly present in all five families. We find that alterations in CHD7 can result in a very mild phenotype, characterized by only a few minor symptoms of the CHARGE syndrome clinical spectrum. Such a mild phenotype was present in two families that shared the same 6322G > A missense mutation. These two families showed parent-to-child transmission. Phenotypically milder forms of CHARGE syndrome have a higher risk of transmission to multiple family members.

Identification of HNPCC by molecular analysis of colorectal and endometrial tumors

Hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) is a dominantly inherited syndrome characterized by the development of colorectal cancer, endometrial cancer and other cancers and the presence of microsatellite instability (MSI) in tumors. The Bethesda guidelines have been proposed for the identification of families suspected of HNPCC that require further molecular analysis. We have evaluated the yield of MSI-analysis in a large series of Dutch families suspected of HNPCC. We also analysed whether the loss of mismatch repair (MMR) protein detected by immunohistochemistry (IHC) of colorectal cancer (CRC) and endometrial cancer correlated with the presence of MSI and/or a MMR gene mutation. The results showed that the Bethesda criteria with a few modifications are appropriate to identify families eligible for genetic testing. In addition, we found that MSI and IHC-analysis of CRC using antibodies against MLH1, MSH2, MSH6 and PMS2 proteins are equally effective for identifying carriers of the known MMR gene defects. However, as long as the role of other putative MMR genes in hereditary CRC has not been elucidated, IHC-analysis cannot completely replace MSI. For this reason, we prefer MSI-analysis as first step in families suspected of HNPCC. On the other hand, in families fulfilling the revised Amsterdam criteria in which the probability of detecting a mutation is relatively high, we would recommend IHC as first diagnostic step because the result might predict the specific underlying MMR gene mutation. MSI or IHC-analysis of endometrial cancer alone was found to be less sensitive compared with these tests performed in colorectal cancer. Therefore, probably the best approach in the analysis of this cancer is to perform both techniques. The identification of HNPCC is important as it makes it possible to target effective preventative measures. Our studies showed that MSI and IHC analysis of colorectal and endometrial cancer, are reliable cost-effective tools that can be used to identify patients with HNPCC.

Microsatellite instability, immunohistochemistry, and additional PMS2 staining in suspected hereditary nonpolyposis colorectal cancer

PURPOSE

Immunohistochemistry (IHC) and microsatellite instability (MSI) analysis can be used to identify patients with a possible DNA mismatch repair defect [hereditary nonpolyposis colorectal carcinoma (HNPCC)]. The Bethesda criteria have been proposed to select families for determination of MSI. The aims of this study were to assess the yield of MSI analysis in families suspected for HNPCC, to compare the results of immunohistochemical staining and MSI analysis, and to assess the additional value of PMS2 staining.

EXPERIMENTAL DESIGN

Clinical data and tumors were collected from 725 individuals from 631 families with suspected HNPCC. MSI analysis was performed using eight markers including the 5 National Cancer Institute markers. Four immunohistochemical staining antibodies were used (MLH1, MSH2, MSH6 and PMS2).

RESULTS

A MSI-H (tumors with instability for >30% of the markers) phenotype in colorectal cancers (CRCs) was observed in 21-49% of families that met the various Bethesda criteria. In families with three cases of CRC diagnosed at age > 50 years, families with a solitary case of CRC diagnosed between ages 45 and 50 years, and families with one CRC case and a first-degree relative with a HNPCC-related cancer, one diagnosed between ages 45 and 50 years (all Bethesda-negative families), the yield of MSI-H was 10-26%. Immunohistochemical staining confirmed the MSI results in 93% of the cases. With IHC, adding PMS2 staining led to the identification of an additional 23% of subjects with an hMLH1 germ-line mutation (35 carriers were tested).

CONCLUSIONS

The Bethesda guidelines for MSI analysis should include families with three or more cases of CRC diagnosed at age > 50 years. The age at diagnosis of CRC in the original guidelines should be raised to 50 years. Routine IHC diagnostics for HNPCC should include PMS2 staining.

Conventional and tissue microarray immunohistochemical expression analysis of mismatch repair in hereditary colorectal tumors

Immunohistochemistry (IHC) of mismatch repair (MMR) proteins in colorectal tumors together with microsatellite analysis (MSI) can be helpful in identifying families eligible for mutation analysis. The aims were to determine sensitivity of IHC for MLH1, MSH2, and MSH6 and MSI analysis in tumors from known MMR gene mutation carriers; and to evaluate the use of tissue microarrays for IHC (IHC-TMA) of colon tumors in its ability to identify potential carriers of MMR gene mutations, and compare it with IHC on whole slides. IHC on whole slides was performed in colorectal tumors from 45 carriers of a germline mutation in one of the MMR genes. The TMA cohort consisted of 129 colon tumors from (suspected) hereditary nonpolyposis colorectal cancer (HNPCC) patients. Whole slide IHC analysis had a sensitivity of 89% in detecting MMR deficiency in carriers of a pathogenic MMR mutation. Sensitivity by MSI analysis was 93%. IHC can also be used to predict which gene is expected to harbor the mutation: for MLH1, MSH2, and MSH6, IHC on whole slides would have correctly predicted the mutation in 48%, 92%, and 75% of the cases, respectively. We propose a scheme for the diagnostic approach of families with (suspected) HNPCC. Comparison of the IHC results based on whole slides versus TMA, showed a concordance of 85%, 95%, and 75% for MLH, MSH2, and MSH6, respectively. This study therefore shows that IHC-TMA can be reliably used to simultaneously screen a large number of tumors from (suspected) HNPCC patients, at first in a research setting.

Two sensitive and rapid chromogenic assays of fondaparinux sodium (Arixtra) in human plasma and other biological matrices

Fondaparinux is a synthetic selective inhibitor of factor Xa recently approved for thromboprophylaxis after major orthopedic surgery. Determination of its concentration gives valuable insight into specific pharmacokinetics or safety studies. The aim of the study was to develop direct, sensitive, precise and accurate assays of fondaparinux sodium in different biological matrices. Consistency with the recommended chromogenic assay for low molecular weight heparin required a similar method. However, recent data indicated some variability in the determination of anti-Xa level between commercial chromogenic assays. Consequently, we developed and validated two chromogenic methods (A and B) for assaying fondaparinux in plasma and other biological matrices. The assays are calibrated with fondaparinux, a pure chemical entity, and the result is expressed as amount (microg) of the fondaparinux calibrator. Results showed that precision was lower than 5.2% in plasma or plasma water and 13% in placental medium. The accuracy was lower than 7.6% in plasma or plasma water and 10.2% in placental medium. The lower limit of quantification in plasma was 0.042 microg/mL with automated Method A and 0.019 microg/mL with Method B. The assay was not affected by the source of the samples, the presence of blood cells, EDTA, citrate or repeated cycles of freezing and thawing. The two chromogenic assays calibrated with fondaparinux sodium reach the equivalence criteria for plasma samples and provide reliable and reproducible results.

Atypical HNPCC owing to MSH6 germline mutations: analysis of a large Dutch pedigree

Hereditary non-polyposis colorectal cancer (HNPCC) is the most common genetic susceptibility syndrome for colorectal cancer. HNPCC is most frequently caused by germline mutations in the DNA mismatch repair (MMR) genes MSH2 and MLH1. Recently, mutations in another MMR gene, MSH6 (also known as GTBP), have also been shown to result in HNPCC. Preliminary data indicate that the phenotype related to MSH6 mutations may differ from the classical HNPCC caused by defects in MSH2 and MLH1. Here, we describe an extended Dutch HNPCC family not fulfilling the Amsterdam criteria II and resulting from a MSH6 mutation. Overall, the penetrance of colorectal cancer appears to be significantly decreased (p<0.001) among the MSH6 mutation carriers in this family when compared with MSH2 and MLH1 carriers (32% by the age of 80 v >80%). Endometrial cancer is a frequent manifestation among female carriers (six out of 13 malignant tumours). Transitional cell carcinoma of the urinary tract is also relatively common in both male and female carriers (10% of the carriers). Moreover, the mean age of onset of both colorectal cancer (MSH6 v MSH2/MLH1 = 55 years v 44/41 years) and endometrial carcinomas (MSH6 v MSH2/MLH1 = 55 years v 49/48 years) is delayed. As previously reported, we confirm that the pattern of microsatellite instability, in combination with immunohistochemical analysis, can predict the presence of a MSH6 germline defect. The detailed characterisation of the clinical phenotype of this kindred contributes to the establishment of genotype-phenotype correlations in HNPCC owing to mutations in specific mismatch repair genes.