Genotype-phenotype correlation in patients suspected of having Sotos syndrome

BACKGROUND

Deletions and mutations in the NSD1 gene are the major cause of Sotos syndrome. We wanted to evaluate the genotype-phenotype correlation in patients suspected of having Sotos syndrome and determine the best discriminating parameters for the presence of a NSD1 gene alteration.

METHODS

Mutation and fluorescence in situ hybridization analysis was performed on blood samples of 59 patients who were clinically scored into 3 groups. Clinical data were compared between patients with and without NSD1 alterations. With logistic regression analysis the best combination of predictive variables was obtained.

RESULTS

In the groups of typical, dubious and atypical Sotos syndrome, 81, 36 and 0% of the patients, respectively, showed NSD1 gene alterations. Four deletions were detected. In 23 patients (2 families) 19 mutations were detected (1 splicing defect, 3 non-sense, 7 frameshift and 8 missense mutations). The best predictive parameters for a NSD1 gene alteration were frontal bossing, down-slanted palpebral fissures, pointed chin and overgrowth. Higher incidences of feeding problems and cardiac anomalies were found. The parameters, delayed development and advanced bone age, did not differ between the 2 subgroups.

CONCLUSIONS

In our patients suspected of having Sotos syndrome, facial features and overgrowth were highly predictive of a NSD1 gene aberration, whereas developmental delay and advanced bone age were not.

Cancer risk in hereditary nonpolyposis colorectal cancer due to MSH6 mutations: impact on counseling and surveillance

BACKGROUND & AIMS

Hereditary nonpolyposis colorectal carcinoma (HNPCC) is caused by a mutated mismatch repair (MMR) gene. The aim of our study was to determine the cumulative risk of developing cancer in a large series of MSH6 mutation carriers.

METHODS

Mutation analysis was performed in 20 families with a germline mutation in MSH6. We compared the cancer risks between MSH6 and MLH1/MSH2 mutation carriers. Microsatellite instability (MSI) analysis and immunohistochemistry (IHC) were performed in the available tumors.

RESULTS

A total of 146 MSH6 mutation carriers were identified. In these carriers, the cumulative risk for colorectal carcinoma was 69% for men, 30% for women, and 71% for endometrial carcinoma at 70 years of age. The risk for all HNPCC-related tumors was significantly lower in MSH6 than in MLH1 or MSH2 mutation carriers (P = 0.002). In female MSH6 mutation carriers, the risk for colorectal cancer was significantly lower (P = 0.0049) and the risk for endometrial cancer significantly higher (P = 0.02) than in MLH1 and MSH2 mutation carriers. In male carriers, the risk for colorectal cancer was lower in MSH6 mutation carriers, but the difference was not significant (P = 0.0854). MSI analysis in colorectal tumors had a sensitivity of 86% in predicting a MMR defect. IHC in all tumors had a sensitivity of 90% in predicting a mutation in MSH6.

CONCLUSIONS

We recommend starting colonoscopic surveillance in female MSH6 mutation carriers from age 30 years. Prophylactic hysterectomy might be considered in carriers older than 50 years. MSI and IHC analysis are sensitive tools to identify families eligible for MSH6 mutation analysis.

Genomic imbalances in mental retardation

INTRODUCTION

It has been estimated that cytogenetically visible rearrangements are present in approximately 1% of newborns. These chromosomal changes can cause a wide range of deleterious developmental effects, including mental retardation (MR). It is assumed that many other cases exist where the cause is a submicroscopic deletion or duplication. To facilitate the detection of such cases, different techniques have been developed, which have differing efficiency as to the number of loci and patients that can be tested.

METHODS

We implemented multiplex amplifiable probe hybridisation (MAPH) to test areas known to be rearranged in MR patients (for example, subtelomeric/pericentromeric regions and those affected in microdeletion syndromes) and to look for new regions that might be related to MR.

RESULTS

In this study, over 30 000 screens for duplications and deletions were carried out; 162 different loci tested in each of 188 developmentally delayed patients. The analysis resulted in the detection of 19 rearrangements, of which approximately 65% would not have been detected by conventional cytogenetic analysis. A significant fraction (46%) of the rearrangements found were interstitial, despite the fact that only a limited number of these loci have so far been tested.

DISCUSSION

Our results strengthen the arguments for whole genome screening within this population, as it can be assumed that many more interstitial rearrangements would be detected. The strengths of MAPH for this analysis are the simplicity, the high throughput potential, and the high resolution of analysis. This combination should help in the future identification of the specific genes that are responsible for MR.

Aberrant polycystin-1 expression results in modification of activator protein-1 activity, whereas Wnt signaling remains unaffected

Polycystin-1, the polycystic kidney disease 1 gene product, has been implicated in several signaling complexes that are known to regulate essential cellular functions. We investigated the role of polycystin-1 in Wnt signaling and activator protein-1 (AP-1) activation. To this aim, a membrane-targeted construct encoding the conserved C-terminal region of mouse polycystin-1 reported to mediate signal transduction activity was expressed in human embryonic and renal epithelial cells. To ensure specificity and minimal cotransfection effects, we focused our study on the endogenous proteins that actually transduce the signals, beta-catenin and T-cell factor/lymphoid-enhancing factor for Wnt signaling and (phosphorylated) c-Jun, ATF2, and c-Fos for AP-1. Our data indicate that the C-terminal region of polycystin-1 activates AP-1 by inducing phosphorylation and expression of at least c-Jun and ATF2, whereas c-Fos was not affected. Under our experimental conditions, polycystin-1 did not modulate Wnt signaling. AP-1 activity was aberrant in human autosomal dominant polycystic kidney disease (ADPKD) renal cystic epithelial cells and in renal epithelial cells expressing transgenic full-length polycystin-1, resulting in decreased Jun-ATF and increased Jun-Fos activity, whereas Wnt signaling remained unaffected. Since our data indicate that aberrant polycystin-1 expression results in altered AP-1 activity, polycystin-1 may be required for adequate AP-1 activity.

No effect of enalapril on progression in autosomal dominant polycystic kidney disease

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors are capable of reducing proteinuria and microalbuminuria with preservation of renal function in diabetic and non-diabetic renal disease. We designed a study investigating the effect of enalapril on the protection of renal function in autosomal dominant polycystic kidney disease (ADPKD).

METHODS

We studied 61 normotensive and 28 hypertensive ADPKD patients. The normotensive group participated in a randomized double-blind placebo-controlled study, using enalapril. The hypertensive group was randomized for open label treatment with enalapril or the beta-blocker atenolol. The follow-up was 3 years, and renal function was established repetitively by measuring the clearance of inulin.

RESULTS

In the normotensive group, renal function at baseline was 112 +/- 3 ml/min and decreased by -8 +/- 2 ml/min (P < 0.001). The loss of renal function in the patients treated with enalapril or placebo was similar (-7 +/- 3 vs -9 +/- 1 ml/min; P = 0.4). Although blood pressure significantly decreased with enalapril treatment, it had no effect on microalbuminuria. In the hypertensive group, renal function at baseline was 89 +/- 2 ml/min. The mean decline in renal function was -12 +/- 2 ml/min (P < 0.001), and was equal in patients treated with enalapril and those treated with atenolol. The patients treated with atenolol required more additional treatment to control blood pressure, but no difference on microalbuminuria was observed between the two treatments.

CONCLUSION

This study was unable to detect a beneficial effect of ACE inhibition on loss of renal function in ADPKD patients.

Abnormal hepatocystin caused by truncating PRKCSH mutations leads to autosomal dominant polycystic liver disease

Mutations in protein kinase C substrate 80K-H (PRKCSH), encoding for the protein hepatocystin, cause autosomal dominant polycystic liver disease (PCLD), which is clinically characterized by the presence of multiple liver cysts. PCLD has been documented in families from Europe (Netherlands, Belgium, Finland) as well as from the United States. In this article, we report results from extensive mutational analysis of the PRKCSH gene in a group of 14 PCLD families and 65 singleton cases of Dutch and Finnish descent with multiple simple liver cysts. We identified PRKCSH mutations in 12 families and in 3 sporadic cases. In 8 of 10 Finnish families we detected the 1437+2delTG splice-site mutation. In Dutch families, we found 2 other mutations that affect correct splicing of PRKCSH: 292+1 G>C (2 families) and 1338-2 A>G (1 family). In another Dutch family, we detected a novel deletion (374-375delAG) in exon 6, predicting an abnormal shortened protein. Investigation of the carrier haplotypes identified a common founder chromosome in unrelated individuals in each of the 3 identified splice-site mutations. In 2 Finnish families with dominantly inherited PCLD, and in 62 of 65 sporadic cases with multiple simple liver cysts, we failed to demonstrate any PRKCSH mutation. This corroborates the notion that autosomal dominant PCLD is genetically heterogeneous. In conclusion, we propose that, on the basis of our results, genetic screening for PRKCSH gene mutations should be limited to patients either with a positive family history for PCLD or who have severe polycystic liver disease.

Large deletions in the polycystic kidney disease 1 (PKD1) gene

Since identification of the genes mutated in patients with Autosomal Dominant Polycystic Kidney Disease, PKD1 and PKD2, a large number of different germ line mutations in both genes have been found by conventional PCR-based mutation detection methods. Nevertheless, in approximately 40% of the PKD1 families the disease-causing mutation remains to be elucidated. Complex germ line rearrangements are often not detectable by these standard diagnostic techniques. To detect large deletions in the PKD1 gene we performed Field Inversion Gel Electrophoresis (FIGE) followed by Southern blot analysis with probes selected in the unique and in the reiterated region of this gene. Our analysis revealed 4 deletions in 125 patients, indicating that large deletions in PKD1 are rare. Likely, patients with a deletion that also affects the neighbouring Tuberous Sclerosis Complex 2 (TSC2) gene will be diagnosed as patients with tuberous sclerosis. It was speculated that the exceptional polypyrimidine tract located in intron 21 and the small tract in intron 22, might play a role in the pathogenesis of ADPKD. Since this region is extremely difficult to amplify by PCR, we analysed the 5.8 kb BamHI fragment that contains the polypyrimidine tracts. We did not observe a disease-linked alteration although we detected two different rare variants either in PKD1 or in one of its homologues.

Altered distribution and co-localization of polycystin-2 with polycystin-1 in MDCK cells after wounding stress

Polycystin-1 and -2 are integral membrane glycoproteins defective in autosomal dominant polycystic kidney disease (ADPKD). Recent studies showed a coupled polycystin-1 and -2 action in cell signaling and channel activation suggesting an important biological role for the two proteins at the plasma membrane. To gain a better understanding about the (co)-distribution and dynamics of the polycystin-1 and -2 complex under stress conditions, we used a wound-healing model of Madine Darby canine kidney (MDCK) renal epithelial cells. In this model, cells near the wound edge undergo a process of reorganization to active migration, while cells further from the edge are unaffected and remain confluent. For the first time, endogenous polycystin-1 and -2 were found to partly co-localize in the plasma membrane of confluent monolayers, and both proteins co-localized in the primary cilium. Upon wound healing, the association of polycystin-2 to the membrane was greatly reduced at the wound edge and the submarginal cells. Polycystin-1 remained incorporated to the membrane at the edge of the cell sheet at all time points, although strongly reduced in lamellipodia-forming cells. Adherens junctions and desmosomes, and respective connected actin and keratin cytoskeleton were also disturbed in lamellipodia-forming cells. We propose that altered subcellular localization of polycystin-1 and -2 as a result of stress will affect signaling and other cellular processes mediated by these proteins.

Bannayan-Riley-Ruvalcaba syndrome: further delineation of the phenotype and management of PTEN mutation-positive cases

Bannayan-Riley-Ruvalcaba syndrome (BRRS) is characterised by macrocephaly, intestinal hamartomatous polyps, lipomas, pigmented maculae of the glans penis, developmental delay and mental retardation. The syndrome follows an autosomal dominant pattern of inheritance. In 1997 reports on two BRRS patients with a deletion at 10q23.2-q24.1 were published. In the same year, the first two families with BRRS and a mutation of the PTEN gene were reported. Mutations in the PTEN gene have also been demonstrated in patients with Cowden syndrome (CS), which shows partial clinical overlap with BRRS, and in families with cases both of BRRS and CS. PTEN mutation positive BRRS and CS are likely to be different phenotypic presentations of the same syndrome. If BRRS and CS are one single condition, the question arises whether patients with BRRS should be screened for malignant tumours, since patients with Cowden syndrome have an increased risk of breast, endometrial, thyroid and renal cancer. We present two isolated cases and one family and confirm that BRRS and CS are allelic. Furthermore, we review the PTEN mutation positive BRRS cases, to further delineate the phenotype and to compare the cases with a genomic deletion with the cases with a point mutation. We recommend offering BRRS cases with a mutation in PTEN the same surveillance protocol for (malignant) tumours as is currently recommended for CS. In addition, we propose a yearly haemoglobin test from early infancy for the early detection of intestinal hamartomas, which are likely to give severe complications, especially in BRRS cases.

Three new families with arterial tortuosity syndrome

Arterial tortuosity syndrome (ATS) is a rare condition with autosomal recessive inheritance characterized by connective tissue abnormalities. The most specific clinical findings are cardiovascular anomalies including tortuosity, lengthening, aneurysm, and stenosis formation of major arteries. Also ventricular hypertrophy is frequently present. Other anomalies are skin hyperextensibility and cutis laxa, joint laxity or contractures of the joints, and inguinal herniae. Histology shows disruption of elastic fibers of the media. These features suggest that ATS is a connective tissue disorder. A biochemical or molecular defect has not yet been identified. We describe here nine additional ATS patients from three consanguineous Moroccan families and review a total of 35 patients with this uncommon condition.

Risk Estimation for Healthy Women from Breast Cancer Families: New Insights and New Strategies

Risk estimation in breast cancer families is often estimated by use of the Claus tables. We analyzed the family histories of 196 counselees; compared the Claus tables with the Claus, the BRCA1/2, the BRCA1/2/ models; and performed linear regression analysis to extend the Claus tables with characteristics of hereditary breast cancer. Finally, we compared the Claus extended method with the Claus, the BRCA1/2, and the BRCA1/2/u models. We found 47% agreement for Claus table versus Claus model; 39% agreement for Claus table versus BRCA1/2 model; 48% agreement for Claus table versus BRCA1/2/u model; 37% agreement for Claus extended method versus Claus model; 44% agreement for Claus extended model versus BRCA1/2 model; and 66% agreement for Claus extended method versus BRCA1/2/u model. The regression formula (Claus extended method) for the lifetime risk for breast cancer was 0.08 + 0.40 (*) Claus Table + 0.07 (*) ovarian cancer + 0.08 (*) bilateral breast cancer + 0.07 (*) multiple cases. This new method for risk estimation, which is an extension of the Claus tables, incorporates information on the presence of ovarian cancer, bilateral breast cancer, and whether there are more than two affected relatives with breast cancer. This extension might offer a good alternative for breast cancer risk estimation in clinical practice.

Genetic Analysis of Short Stature

Short stature is a major concern for patients and their parents, and represents a diagnostic challenge to the clinician. A correct diagnosis is of particular importance in view of the availability of effective, but costly, therapy in a small subset of cases. Many different genetic etiologies of short stature are known. Therefore, chromosome as well as molecular analysis are requisite diagnostic investigations in children with short stature. Particularly in the group of children with idiopathic short stature, possibilities of molecular analysis are often underestimated. Important options are UPD7 and the FGFR3, SHOX, GH1 and GHR genes. Furthermore, analysis of the IGF and IGF1R genes should be considered. We propose a flow chart for molecular analysis in short stature.

Evaluation of diagnostic NOTCH3 immunostaining in CADASIL

CADASIL is caused by mutations in the NOTCH3 gene. Although increasingly recognized as a disease entity, the diagnostic confirmation can be lengthy or inconclusive. Recently, NOTCH3 immunostaining of skin biopsy specimens has been introduced as a new diagnostic test. The aim of this study was to independently assess the diagnostic value of NOTCH3 immunostaining, and determine whether the degree of immunostaining correlates with other disease parameters. We determined NOTCH3 mutation carrier status in 62 symptomatic and asymptomatic individuals from 15 CADASIL families. Skin biopsy specimens of these individuals, as well as of a disease control group, were immunostained with NOTCH3 antibody and blindly analyzed by two independent observers to determine sensitivity and specificity. A semiquantitative NOTCH3 immunostaining score was correlated with clinical, genetic and MRI parameters. The sensitivity was 90.2% and 85.4%, respectively, for the two observers, the specificity 95.2% and 100%; both lower than previously reported. Certain NOTCH3 mutations may underlie false-negative results. False-positive results were found in a non-mutated control, and also in one disease control. There was no difference in immunostaining between symptomatic and asymptomatic NOTCH3 mutated individuals. Furthermore, the NOTCH3 immunostaining score did not correlate with clinical or MRI parameters. NOTCH3 immunostaining is a supportive, but not definitive, CADASIL diagnostic test, and should be interpreted in the context of clinical and radiological data. Confirmation by DNA analysis is requisite for positive results, and when there exists high clinical suspicion, also for negative results.

Myocardial infarction in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an angiopathy caused by mutations in the NOTCH3 gene. Typical microvascular changes are found throughout the arterial tree, but the documented disease expression is confined to the central nervous system. In an ongoing CADASIL study, we noted a number of patients with early acute myocardial infarction (before the age of 50 years), as well as patients with electrocardiogram (ECG) abnormalities. We analyzed these data to determine whether myocardial ischemia is associated with NOTCH3 mutations. ECGs were recorded in mutated (n = 41) and nonmutated (n = 22) individuals from 15 genetically confirmed CADASIL families, and blindly classified according to the Minnesota code. Cardiologic history was assessed and cardiovascular disease risk factors were determined. Evidence for myocardial infarction was defined as a positive history for acute myocardial infarction and/or a Minnesota Code 1 (Q-waves) on ECG. We examined CADASIL myocardial tissue ultrastructurally and immunohistochemically for evidence of microangiopathy. We found that almost 25% (10/41) of mutation carriers had evidence of myocardial infarction, versus none of the 22 nonmutation carriers (p = 0.011). Five had a medical history of acute myocardial infarction, and 5 had current pathologic Q-waves on ECG. Acute myocardial infarction occurred at a mean age of 39.6 +/- 5.22 years, and predated major neurologic symptoms of CADASIL in all cases. Pathologic examination of myocardial tissue revealed typical CADASIL arteriopathic changes of the coronary microvasculature. To our knowledge, this is the first study showing that NOTCH3 mutation carriers may be at increased risk of early acute myocardial infarction, expanding CADASIL disease expression beyond the central nervous system to include the heart.

Genetic counselling and the intention to undergo prophylactic mastectomy: effects of a breast cancer risk assessment

Scientific reports suggest that women at risk for familial breast cancer may benefit from prophylactic mastectomy. However, few data are available about how women decide upon this clinical option, and in particular, what role an objective risk assessment plays in this. The purpose of the present study is to assess whether this objective risk information provided in genetic counselling affects the intention for prophylactic mastectomy. Additionally, the (mediating) effects of breast cancer worry and perceived risk are investigated. A total of 241 women completed a questionnaire before and after receiving information about their familial lifetime breast cancer risk in a genetic counselling session. Path analysis showed that the objective risk information had a corrective effect on perceived risk (beta=0.38; P=0.0001), whereas the amount of breast cancer worry was not influenced by the counselling session. The objective risk information did not directly affect the intention for prophylactic mastectomy. The intention was influenced by perceived risk after counselling (beta=0.23; P=0.002), and by the precounselling levels of perceived risk (beta=0.27; P=0.00025) and breast cancer worry (beta=0.32; P=0.0001), that is, higher levels of perceived risk and breast cancer worry imply a stronger intention for prophylactic mastectomy. A personal history of breast cancer did not directly influence the intention for prophylactic mastectomy, but affected women who had undergone a mastectomy as surgical treatment were more positively inclined to have a prophylactic mastectomy than women who had had breast-conserving therapy. The impact of objective risk information on the intention for prophylactic mastectomy is limited and is mediated by perceived risk. Important determinants of the intention for prophylactic mastectomy were precounselling levels of breast cancer worry and perceived risk, suggesting that genetic counselling is only one event in the entire process of decision making. Therefore, interventions aimed at improving decision making on prophylactic mastectomy should explicitly address precounselling factors, such as personal beliefs and the psychological impact of the family medical history.

Somatic mosaicism of a point mutation in the dystrophin gene in a patient presenting with an asymmetrical muscle weakness and contractures

We describe a patient with somatic mosaicism of a point mutation in the dystrophin gene causing benign muscular dystrophy with an unusual asymmetrical distribution of muscle weakness and contractures. To our knowledge this is the first patient with asymmetrical weakness and contractures in an ambulatory patient with a dystrophinopathy.

Incipient CADASIL

BACKGROUND

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is caused by mutations in the NOTCH3 gene. Knowledge of disease expression in young adult NOTCH3 mutation carriers (MCs) is limited.

OBJECTIVE

To characterize clinical, neuropsychological, and radiological status in NOTCH3 MCs younger than 35 years.

DESIGN

Clinical characterization and blinded survey comparing MCs with non-MCs.

SETTING

Referral center.

PARTICIPANTS

Individuals younger than 35 years who were at a 50% risk of a NOTCH3 mutation, from our CADASIL database. Thirteen individuals, from 8 families, met the criteria.

METHODS

Comprehensive clinical, genetic, neuropsychological, and radiological investigations. Magnetic resonance images were scored according to a standardized white matter hyperintensities rating scale.

RESULTS

Six individuals, from 5 families, were MCs. Clinical symptoms consisted of migraine (with aura), stroke, and stroke-like episodes. We did not find evidence for psychiatric disturbances, functional disability, or cognitive dysfunction, compared with non-MCs. Radiologically, a characteristic magnetic resonance imaging lesion pattern emerged for all MCs. This comprised white matter hyperintensities in the anterior temporal lobes, the frontal lobes, and the periventricular frontal caps.

CONCLUSIONS

Migraine (with aura) and stroke can present in NOTCH3 MCs younger than 35 years; however, more importantly, physical function and cognition are intact. Possible subtle cognitive dysfunction needs to be assessed in a larger study. White matter hyperintensities on magnetic resonance imaging are characteristic, and are consistently visualized from the age of 21 years and onward. Awareness of the clinical and radiological features of CADASIL in those younger than 35 years should increase early diagnosis and allow for customized counseling of young adults from families with CADASIL.

Loss of CBP acetyltransferase activity by PHD finger mutations in Rubinstein-Taybi syndrome

Disruption of one copy of the human CREB binding protein (CBP or CREBBP) gene leads to the Rubinstein-Taybi syndrome (RTS), a developmental disorder characterized by retarded growth and mental functions, broad thumbs, broad big toes and typical facial abnormalities. The CREB binding protein (CBP) is an essential transcriptional coactivator for many different transcription factors. CBP has the intrinsic ability to acetylate histones and other proteins, which is regarded as an important step in transcription activation. In vitro studies have shown that this enzymatic activity critically depends on the integrity of a plant homeodomain (PHD)-type zinc finger in the HAT domain of CBP. We therefore investigated whether PHD finger mutations are present in RTS patients. Mutational analysis of 39 patients revealed eight novel heterozygous mutations in the HAT domain of CBP, one of which alters a conserved PHD finger amino acid (E1278K), while a second mutation deletes exon 22, which encodes the central region of the PHD finger. Functional analysis of these RTS-associated PHD finger mutants showed that they lacked in vitro acetyltransferase activity towards histones and CBP itself and displayed reduced coactivator function for the transcription factor CREB. Importantly, in EBV-transformed lymphoblastoid cells from the exon 22 deletion patient we found approximately 50% less endogenous CBP HAT activity. These findings therefore underscore the functional importance of the PHD finger in vivo and imply that reduction of CBP HAT activity, as exemplified here by disruption of the PHD finger, is sufficient to cause RTS.

[From gene to disease; SLC3A1, SLC7A9 and cystinuria]

In total, 1-2% of adults and 6-8% of children suffering from kidney stones have cystinuria, a defect in the transport of amino acids, which leads to high concentrations of cystine in the urine. Two genes have been implicated, solute carrier family 3 (cystine, basic and) neutral amino acid transporter, member 1 (SLC3A1) coding for the protein related to the system bo,+ amino-acid transporter, and solute carrier family 7, member 9 (SLC7A9), coding for the protein bo,+AT. There are three clinically defined types of cystinuria. Type I (autosomal recessive) is characterised by mutations in the SLC3A1 gene; carriers have normal cystine levels in urine. In total 80% of non-type-I patients have a detectable mutation in the SLC7A9 gene. First-degree relatives of a patient with type 2 (dominant) or type 3 (incomplete recessive) cystinuria may have slightly elevated cystine levels in the urine. The early recognition and treatment of cystinuria is important because recurrent stone formation may lead to urinary tract infection and, eventually, renal failure.

Testing the test--why pursue a better test for Huntington disease?

In 1993, the gene mutation for Huntington disease (HD) was identified and testing became possible with a reliability of >99%, without the need for co-operation of relatives. In 1997, a systematic information program offered the mutation retest to individuals who had earlier received a linkage test result for HD, which has a residual uncertainty of 1-9%. The characteristics of 129 individuals tested by linkage analysis for HD are reported on, as well as the reasons for their reassessment by mutation testing. Three groups were compared: (1) people who were retested between 1993 and 1997, before this study had started, (2) people who were retested after we provided information, and (3) persons who refrained from retesting. Nearly half of the linkage-tested individuals were retested, with the exception of noncarriers with a residual risk of 1 or 2%. Of them, less than one out of five were retested. Carriers with a hopeful view on the future (BHS) and a better sense of well-being (GHQ) were more likely to have the retest. Female carriers were also more likely to have the retest before we contacted them. Noncarriers who were retested were more anxious (HADS) than noncarriers who refrained from the retest. Retestees were younger at the time of testing. No risk reversals were revealed by this study.

Dominant hemochromatosis due to N144H mutation of SLC11A3: clinical and biological characteristics

Hereditary hemochromatosis is classically inherited as a recessive trait but is genetically heterogeneous. Mutations in the HFE and the TFR2 genes account for about 80% of patients and a third locus on chromosome 1q is responsible for juvenile hemochromatosis. We describe here the clinical and biological characteristics of autosomal dominant form of iron overload due to the N144H mutation of the SLC11A3 gene. Clinical signs of iron overload in patients include joint pains, cardiomyopathies, liver fibrosis and hormonal disorders including diabetes mellitus. The main and most common clinical symptoms in this family were joint complaints and early signs of arthrosis. Serum ferritin levels in iron overloaded subjects varied from 31 to 2179 ng/ml and the transferrin saturation from 13 to 88.6%. The iron overload is moderate compared to patients with type 1 hemochromatosis but the deferoxamine test was normal in all patients. The disease in this family segregated as a dominant trait. None of the patients was homozygous or compound heterozygous for any known mutation in the HFE or TFR2 genes. The disease in this family represents a non-classical form of iron overload caused by the N144H mutation in the SLC11A3 gene. The reports of other distinct mutations in SLC11A3 suggest that this gene may be of interest for further etiologic research.

[Phenotypic variability: genetics and chance--deletion 22q11 and schizophrenia]

Haploinsufficiency syndromes, such as the deletion 22q11, the velo-cardio-facial or DiGeorge/Shprintzen syndrome characterised by chromosome 22q11 deletion, show marked variability in the clinical features. This variability may be due to chance fluctuations in expression of genes in the deleted segment, which tend to have more impact if only one copy of the gene is present. The apparent association between deletion 22q11 and schizophrenia indicates a role for a gene within the deletion in signal transduction in the brain.