Carriers Of Pathogenic Mutations Research Articles

Abstract 18: Molecular characterization of Brazilian patients suspected for Lynch syndrome

Abstract Lynch syndrome (LS), former known as Hereditary Non Polyposis Colorectal cancer (HNPCC), accounts for 3-5% of all colorectal cancers (CRC) and is inherited in an autossomal dominant fashion. This syndrome is characterized by early CRC onset, high incidence of tumors in the ascending colon, excess of synchronous and metachronous tumors, and accelerated transition adenoma-carcinoma (2-3 years). Nowadays, LS is regarded of patients who carry deleterious germline mutations in one of the five Mismatch repair genes, such as MutL homolog 1 (MLH1), MutS homolog 2 (MSH2), MutS homolog 6 (MSH6), post-meiotic segregation increased 1 (PMS1) or post-meiotic segregation increased 2 (PMS2). In order to characterize Brazilian patients suspect for LS, we assessed the frequency of germline point mutations in MSH6, PMS1 and PMS2 in patients negative for point mutations in MLH1 and MSH2 by capillary sequencing. We also assessed chromosomal deletions in MLH1 and MSH2 and MSH6 generating a complete characterization of MMR genes. The analysis of the five MMR genes revealed 46 carriers of pathogenic mutations, including 25 in MSH2 (54%), 16 in MLH1 (35%), 4 in MSH6 (9%) and one in PMS2 (2%) gene In addition, from the 70 negative patients, we selected one mutation negative family that met the stringent Amsterdam criteria (AC) for whole exome sequencing using the SOLID platform. For this family, we selected 5 close blood relatives, including 3 affected and 2 unaffected individuals in order to facilitate the identification of new susceptibility genes with autosomal dominant pattern. The results revealed two candidate genes, c-KIT and WDR27 that segregated with the disease. Additional analysis are under evaluation. Citation Format: Felipe C. Silva, Giovana T. Torrezan, Márcia CP Figueiredo, Jose Roberto O. Ferreira, Érika M. Santos, Wilson T. Nakagawa, Samuel Aguiar-Junior, Benedito M. Rossi, Fabio O. Ferreira, Dirce M. Carraro. Molecular characterization of Brazilian patients suspected for Lynch syndrome. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Susceptibility and Cancer Susceptibility Syndromes; Jan 29-Feb 1, 2014; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(23 Suppl):Abstract nr 18. doi:10.1158/1538-7445.CANSUSC14-18

Clinical phenotype in heterozygote and biallelic Bernard-Soulier syndrome--a case control study.

Bernard-Soulier syndrome (BSS) is a rare severe autosomal recessive bleeding disorder. To date heterozygous carriers of BSS mutations have not been shown to have bleeding symptoms. We assessed bleeding using a semi-quantitative questionnaire, platelet parameters, PFA-100 closure times, ristocetin response, GP Ib/IX expression and VWF antigen in 14 BSS patients, 30 heterozygote carriers for related mutations and 29 controls. Eight mutations in GP1BA, GP1BB or GP9 were identified including four previously unknown pathogenic mutations. Subjects with BSS reported markedly more mucocutaneous bleeding than controls. Increased bleeding was also observed in heterozygotes. Compared to controls, patients with BSS had lower optical platelet counts (P < 0.001), CD61-platelet counts (P < 0.001) and higher mean platelet volume (17.7 vs. 7.8 fL, P < 0.001) and ristocetin response and closure times were unmeasurable. Heterozygotes had higher MPV (9.7 fL, P < 0.001) and lower platelet counts (P < 0.001) than controls but response to ristocetin and closure times were normal. The VWF was elevated in both BSS and in heterozygotes (P = 0.005). We conclude that heterozygotes for BSS mutations have lower platelet counts than controls and show a bleeding phenotype albeit much milder than in BSS. Both patients with BSS and heterozygote carriers of pathogenic mutations have raised VWF.

Current novel-gene-finding strategy for autosomal-dominant hypercholesterolaemia needs refinement

AimsAutosomal-dominant hypercholesterolaemia (ADH) is a heterogeneous common disorder, and uncovering the molecular determinants that underlie ADH is a major focus of cardiovascular research. However, despite rapid technical advances, efforts to...

A.P.15: Severe early onset cardiomyopathy in females with Danon disease is not caused by skewed X-chromosome inactivation

Danon disease is caused by mutations in the lysosome-associated membrane protein-2 gene, LAMP2, which is located on the X chromosome. Female carriers may occasionally present already in childhood with cardiomyopathy and a very severe disease course. It has been proposed that this is a result of unfavorable skewing of X-chromosome inactivation. We have investigated two young girls aged ten and thirteen years who underwent cardiac transplantation because of cardiomyopathy due to de novo heterozygous LAMP2 mutations. We also investigated one adult female with a more typical clinical phenotype. We found no evidence of skewed X-chromosome inactivation in the two young girls. In accordance with this finding skeletal muscle biopsy revealed no pathological changes. Expression of LAMP2 mRNA in cardiac muscle in the youngest patient revealed equal expression of both alleles also supporting the concept that there was no skewed X-chromosome inactivation. Immunohistochemistry in cardiac muscles of all three patients showed an unexpected and remarkable pattern with lack of LAMP2 protein large regions that also showed myocyte hypertrophy, disarray and lysosomal enlargement. In other large regions there was preserved LAMP2 expression and nearly normal histology. Our results demonstrate that skewed X-chromosome inactivation may not be a common cause of the severe cardiac phenotype seen in occasional female carriers of pathogenic LAMP2 mutations. Instead an uneven distribution of LAMP2 protein may cause deleterious effects depending on which regions of the myocardium that are lacking LAMP2 protein in spite of an overall moderate reduction of LAMP2 protein.

Arrhythmogenic cardiomyopathy: diagnosis, genetic background, and risk management.

Arrhythmogenic cardiomyopathy (AC), also known as arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C), is a hereditary disease characterised by ventricular arrhythmias, right ventricular and/or left ventricular dysfunction, and fibrofatty replacement of cardiomyocytes. Patients with AC typically present between the second and the fourth decade of life with ventricular tachycardias. However, sudden cardiac death (SCD) may be the first manifestation, often at young age in the concealed stage of disease. AC is diagnosed by a set of clinically applicable criteria defined by an international Task Force. The current Task Force Criteria are the essential standard for a correct diagnosis in individuals suspected of AC. The genetic substrate for AC is predominantly identified in genes encoding desmosomal proteins. In a minority of patients a non-desmosomal mutation predisposes to the phenotype. Risk stratification in AC is imperfect at present. Genotype-phenotype correlation analysis may provide more insight into risk profiles of index patients and family members. In addition to symptomatic treatment, prevention of SCD is the most important therapeutic goal in AC. Therapeutic options in symptomatic patients include antiarrhythmic drugs, catheter ablation, and ICD implantation. Furthermore, patients with AC and also all pathogenic mutation carriers should be advised against practising competitive and endurance sports.

Outcomes of adrenal-sparing surgery or total adrenalectomy in phaeochromocytoma associated with multiple endocrine neoplasia type 2: an international retrospective population-based study

The prevention of medullary thyroid cancer in patients with multiple endocrine neoplasia type 2 syndrome has demonstrated the ability of molecular diagnosis and prophylactic surgery to improve patient outcomes. However, the other major neoplasia associated with multiple endocrine neoplasia type 2, phaeochromocytoma, is not as well characterised in terms of occurrence and treatment outcomes. In this study, we aimed to systematically characterise the outcomes of management of phaeochromocytoma associated with multiple endocrine neoplasia type 2. This multinational observational retrospective population-based study compiled data on patients with multiple endocrine neoplasia type 2 from 30 academic medical centres across Europe, the Americas, and Asia. Patients were included if they were carriers of germline pathogenic mutations of the RET gene, or were first-degree relatives with histologically proven medullary thyroid cancer and phaeochromocytoma. We gathered clinical information about patients'RET genotype, type of treatment for phaeochromocytoma (ie, unilateral or bilateral operations as adrenalectomy or adrenal-sparing surgery, and as open or endoscopic operations), and postoperative outcomes (adrenal function, malignancy, and death). The type of surgery was decided by each investigator and the timing of surgery was patient driven. The primary aim of our analysis was to compare disease-free survival after either adrenal-sparing surgery or adrenalectomy. 1210 patients with multiple endocrine neoplasia type 2 were included in our database, 563 of whom had phaeochromocytoma. Treatment was adrenalectomy in 438 (79%) of 552 operated patients, and adrenal-sparing surgery in 114 (21%). Phaeochromocytoma recurrence occurred in four (3%) of 153 of the operated glands after adrenal-sparing surgery after 6-13 years, compared with 11 (2%) of 717 glands operated by adrenalectomy (p=0.57). Postoperative adrenal insufficiency or steroid dependency developed in 292 (86%) of 339 patients with bilateral phaeochromocytoma who underwent surgery. However, 47 (57%) of 82 patients with bilateral phaeochromocytoma who underwent adrenal-sparing surgery did not become steroid dependent. The treatment of multiple endocrine neoplasia type 2-related phaeochromocytoma continues to rely on adrenalectomies with their associated Addisonian-like complications and consequent lifelong dependency on steroids. Adrenal-sparing surgery, a highly successful treatment option in experienced centres, should be the surgical approach of choice to reduce these complications.

Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy and Cardiac Sarcoidosis

Background— Cardiac sarcoidosis (CS) may show overlap in the clinical presentation with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). We sought to investigate patients with CS who were misdiagnosed with ARVD/C and identify clinical features to distinguish these 2 groups. Methods and Results— Among patients enrolled in the Johns Hopkins ARVD/C registry, 15 patients with definite 2010 diagnostic criteria for ARVD/C were subsequently diagnosed with CS. Forty-two pathogenic desmosomal mutation carriers with definite ARVD/C based on the 2010 diagnostic criteria served as a control group. Patients with CS were older at the age of symptom onset, more likely to have comorbidities, and develop heart failure symptoms over time ( P &lt;0.05). Electrocardiographically, PR interval prolongation and high-grade atrioventricular block were exclusively associated with CS ( P &lt;0.05). HV interval prolongation and increased number of ventricular tachycardias induced were also associated with CS ( P &lt;0.05). Radiographically, significant left ventricular dysfunction, myocardial delayed enhancement of the septum, and mediastinal lymphadenopathy were more often see in those with CS ( P &lt;0.05). Conclusions— The 2010 diagnostic criteria for ARVD/C have limited discrimination in distinguishing between ARVD/C and CS. Despite the overlay in clinical presentation, older age of symptom onset, presence of cardiovascular comorbidities, nonfamilial pattern of disease, PR interval prolongation, high-grade atrioventricular block, significant left ventricular dysfunction, myocardial delayed enhancement of the septum, and mediastinal lymphadenopathy should raise the suspicion for CS.

The presentation of an asymptomatic ovarian carcinosarcoma caught by BRCA1 mutation surveillance program

Women with the BRCA1/2 mutations, which cause hereditary breast and ovarian cancer (HBOC), are 35–40 times more likely to develop ovarian cancer compared with the general population. We treated a patient in whom ovarian carcinosarcoma was identified during surveillance for HBOC. She had suffered from breast cancer at ages 45 and 50. At the age of 54 years, she was diagnosed as carrying an “uncertain significant” BRCA1 variant using a genetic mutation analysis. She was referred to our department, and surveillance was performed every 3–6 months for BRCA1 pathogenic mutation carriers due to her family history. At the age of 62 years, cervical and endometrial cytology suggested a diagnosis of adenocarcinoma. At this point, the CA125 level was 19.7 and positron emission tomography/computed tomography (PET/CT) images revealed a right ovarian tumor (SUVmax, 7.41). Surgery was performed, and ovarian carcinosarcoma (pT3cN0M0) was diagnosed. Adjuvant chemotherapy consisting of paclitaxel and carboplatin was initiated. In the month during which the cancer was identified, BRCA1 variant mutation was re-designated as “suspected deleterious,” and 8 years after the initial genetic diagnosis, the causative mutation was identified. The patient has been disease-free for 4 years since surgery. This case demonstrates both the importance and difficulty of surveillance.

Arrhythmogenic ventricular cardiomyopathy: A paradigm shift from right to biventricular disease.

Arrhythmogenic ventricular cardiomyopathy (AVC) is generally referred to as arrhythmogenic right ventricular (RV) cardiomyopathy/dysplasia and constitutes an inherited cardiomyopathy. Affected patients may succumb to sudden cardiac death (SCD), ventricular tachyarrhythmias (VTA) and heart failure. Genetic studies have identified causative mutations in genes encoding proteins of the intercalated disk that lead to reduced myocardial electro-mechanical stability. The term arrhythmogenic RV cardiomyopathy is somewhat misleading as biventricular involvement or isolated left ventricular (LV) involvement may be present and thus a broader term such as AVC should be preferred. The diagnosis is established on a point score basis according to the revised 2010 task force criteria utilizing imaging modalities, demonstrating fibrous replacement through biopsy, electrocardiographic abnormalities, ventricular arrhythmias and a positive family history including identification of genetic mutations. Although several risk factors for SCD such as previous cardiac arrest, syncope, documented VTA, severe RV/LV dysfunction and young age at manifestation have been identified, risk stratification still needs improvement, especially in asymptomatic family members. Particularly, the role of genetic testing and environmental factors has to be further elucidated. Therapeutic interventions include restriction from physical exercise, beta-blockers, sotalol, amiodarone, implantable cardioverter-defibrillators and catheter ablation. Life-long follow-up is warranted in symptomatic patients, but also asymptomatic carriers of pathogenic mutations.

Progranulin Peripheral Levels as a Screening Tool for the Identification of Subjects with Progranulin Mutations in a Portuguese Cohort

Background: Progranulin (PGRN) mutations are associated with different clinical phenotypes, including frontotemporal lobar degeneration (FTLD), corticobasal syndrome (CBS) and Alzheimer's disease (AD). As all pathogenic PGRN mutations identified so far cause disease through haploinsufficiency, determination of PGRN levels has been proposed as a reliable method to identify mutation carriers. Objective: To evaluate the accuracy of peripheral PGRN levels in the identification of the PGRN mutation carriers detected thus far in our Portuguese cohort. Methods: Serum PGRN levels were measured in 244 subjects (124 patients in the spectrum of FTLD, 2 asymptomatic descendants of a FTLD patient, 56 AD patients and 64 controls) by a novel commercial ELISA kit. Results: Low PGRN levels were detected in 7 individuals (5 behavioral variant frontotemporal dementia, 1 CBS, and 1 still clinically unaffected) that constituted the group of the null PGRN mutation carriers previously identified in our molecular diagnostic laboratory. The pathogenic mutations found consisted of 4 insertion-deletions, causing frameshifts resulting in premature stop codons, 3 of which were novel. In addition, a normal PGRN level was found in a patient harboring a novel missense variant. For this novel ELISA kit, we established a PGRN cut-off level that identified with 100% accuracy the pathogenic mutation carriers. Conclusion: This study supports the use of a novel assay for the determination of PGRN levels as a screening procedure to identify patients harboring null PGRN mutations. This approach would significantly decrease the required PGRN mutation analysis workload and should be extended to other clinical phenotypes than behavioral variant frontotemporal dementia and to apparently sporadic cases.

Mutations at the SLC20A2 gene and brain resilience in families with idiopathic basal ganglia calcification (“Fahr's disease”)

Mutations at the SLC20A2 gene and brain resilience in families with idiopathic basal ganglia calcification (“Fahr's disease”)

Risks of Less Common Cancers in Proven Mutation Carriers With Lynch Syndrome

Patients with Lynch syndrome are at high risk for colon and endometrial cancer, but also at an elevated risk for other less common cancers. The purpose of this retrospective cohort study was to provide risk estimates for these less common cancers in proven carriers of pathogenic mutations in the mismatch repair (MMR) genes MLH1, MSH2, and MSH6. Data were pooled from the German and Dutch national Lynch syndrome registries. Seven different cancer types were analyzed: stomach, small bowel, urinary bladder, other urothelial, breast, ovarian, and prostate cancer. Age-, sex- and MMR gene-specific cumulative risks (CRs) were calculated using the Kaplan-Meier method. Sex-specific incidence rates were compared with general population incidence rates by calculating standardized incidence ratios (SIRs). Multivariate Cox regression analysis was used to estimate the impact of sex and mutated gene on cancer risk. The cohort comprised 2,118 MMR gene mutation carriers (MLH1, n = 806; MSH2, n = 1,004; MSH6, n = 308). All cancers were significantly more frequent than in the general population. The highest risks were found for male small bowel cancer (SIR, 251; 95% CI, 177 to 346; CR at 70 years, 12.0; 95% CI, 5.7 to 18.2). Breast cancer showed an SIR of 1.9 (95% CI, 1.4 to 2.4) and a CR of 14.4 (95% CI, 9.5 to 19.3). MSH2 mutation carriers had a considerably higher risk of developing urothelial cancer than MLH1 or MSH6 carriers. The sex- and gene-specific differences of less common cancer risks should be taken into account in cancer surveillance and prevention programs for patients with Lynch syndrome.

Frequency of mutations in mismatch repair genes in a population-based study of women with ovarian cancer

Background:Mutations in genes for hereditary non-polyposis colorectal cancer (HNPCC) in ovarian cancer patients remains poorly defined. We sought to estimate the frequency and characteristics of HNPCC gene mutations in a population-based sample of women with epithelial ovarian cancer.Methods:The analysis included 1893 women with epithelial ovarian cancer ascertained from three population-based studies. Full-germline DNA sequencing of the coding regions was performed on three HNPCC genes, MLH1, MSH2 and MSH6. Collection of demographic, clinical and family history information was attempted in all women.Results:Nine clearly pathogenic mutations were identified, including five in MSH6, two each in MLH1 and MSH2. In addition, 28 unique predicted pathogenic missense variants were identified in 55 patients. Pathogenic mutation carriers had an earlier mean age at diagnosis of ovarian cancer, overrepresentation of cancers with non-serous histologies and a higher number of relatives with HNPCC-related cancers.Conclusions:Our findings suggest that fewer than 1% of women with ovarian cancer harbour a germline mutation in the HNPCC genes, with overrepresentation of MSH6 mutations. This represents a lower-range estimate due to the large number of predicted pathogenic variants in which pathogenicity could not definitively be determined. Identification of mismatch repair gene mutations has the potential to impact screening and treatment decisions in these women.

Back to the future: From genome to metabolome

In the traditional medical genetics setting, metabolic disorders, identified either clinically or through biochemical screening, undergo subsequent single gene testing to molecularly confirm diagnosis, provide further insight on natural disease history, and inform on disease management, treatment, familial testing, and reproductive options. For decades now, this process has been responsible for saving many lives worldwide. Only recently, though, has it become possible to move in the opposite direction by starting with an individual's whole genome or exome, and, guided by this data, study more minor perturbations in the absolute values and substrate ratios of clinically important biochemical analytes. Genomic individuality can also be used to guide more detailed phenotyping aimed at uncovering milder manifestations of known metabolic diseases. Metabolomic phenotyping in the Personal Genome Project for our first 200+ participants-all of whom are scheduled to have full genome sequence at more than 40× coverage available by May 2012-is aimed at uncovering potential subclinical and preclinical disease states in carriers of known pathogenic mutations and in lesser known rare variants that are protein predicted to be pathogenic. Our initial focus targets 88 genes involved in 68 metabolic disturbances with established evidence-based nutritional and/or pharmacological therapy as part of standard medical care.

Deep sequencing of theLRRK2gene in 14,002 individuals reveals evidence of purifying selection and independent origin of the p.Arg1628Pro mutation in Europe

Genetic variation in LRRK2 predisposes to Parkinson disease (PD), which underpins its development as a therapeutic target. Here, we aimed to identify novel genotype-phenotype associations that might support developing LRRK2 therapies for other conditions. We sequenced the 51 exons of LRRK2 in cases comprising 12 common diseases (n = 9,582), and in 4,420 population controls. We identified 739 single-nucleotide variants, 62% of which were observed in only one person, including 316 novel exonic variants. We found evidence of purifying selection for the LRRK2 gene and a trend suggesting that this is more pronounced in the central (ROC-COR-kinase) core protein domains of LRRK2 than the flanking domains. Population genetic analyses revealed that LRRK2 is not especially polymorphic or differentiated in comparison to 201 other drug target genes. Among Europeans, we identified 17 carriers (0.13%) of pathogenic LRRK2 mutations that were not significantly enriched within any disease or in those reporting a family history of PD. Analysis of pathogenic mutations within Europe reveals that the p.Arg1628Pro (c4883G>C) mutation arose independently in Europe and Asia. Taken together, these findings demonstrate how targeted deep sequencing can help to reveal fundamental characteristics of clinically important loci.

Pharmacological Approaches for BRCA1/2 Related Breast and Ovarian Cancer: Preclinical Studies and Early Clinical Trials

The identification of BRCA1 and BRCA2 genes has led to the understanding of the molecular basis of the Hereditary Breast and Ovarian Cancer Syndromes and to the development of preventive strategies by the identification of individuals carriers of pathogenic germ-line mutations. In the last few years the study of the complex molecular scenario of breast and ovarian tumors arising in the BRCA1 and 2 setting has opened new exciting treatment perspectives on the basis of the important defects in DNA repair which are linked to BRCA1/2 related carcinogenesis. Early clinical trials have clearly demonstrated the translational value of preclinical research on Cisplatin or Poly-ADP-ribose inhibitors. A new treatment paradigma is now emerging which links cancer treatment to the carcinogenetic process and whose value will probably spread beyond the specific setting of inherited breast and ovarian cancer.

Pathogenic germline TP53 mutations in adult sarcoma patients; implications for treatment and screening – description of an upcoming project

Identification and clinical annotation of risk alleles is critical for young people with sarcoma for several reasons. The mutated gene can be passed onto the next generation affecting reproductive choices. In addition, the risk of a second malignancy appears to be markedly increased in some patients. Thirdly, the risk to other relatives, parents and siblings may vary from 50% to an unquantifiable risk. Finally, ionizing radiation increases cancer risk synergistically in the presence of mutations in sarcoma genes such as Rb and TP53 and diagnostic and therapeutic radiation is modifiable in high risk individuals provided such mutations are identified. The primary aim of this project will be seeking to establish whether the detection of pathogenic germline TP53 mutations in adult sarcoma patients can improve outcomes through tailored clinical management. These patients have been recruited through the International Sarcoma Kindred Study (ISKS). This project will have access to the ISKS biospecimens, pedigree data, genetic information and data associated with clinical outcomes. The ISKS currently has 450 adult sarcoma probands, with recruitment on going. To date, sequencing has already been performed on 272 of these probands, in which 12 pathogenic mutations have been detected (4%). Index cases with an identified pathogenic TP53 mutation and their families will be systematically followed up to ascertain outcomes and to recruit further family members. The genetic status of this cohort will be collated with their clinical characteristics through examination of medical records and family history through pedigree data. The clinical outcomes of the identified pathogenic TP53 mutation carriers and treatments given will be documented and compared against affected non-mutation carriers using a pseudo case-control study design to assess how the effects of treatment combine with mutation status. A further aim of this project will be to conduct analyses nested within the whole ISKS cohort to seek to establish the pathogenicity of unclassified variants that have been detected so far in the ISKS cohort. This analysis will be twofold with the first part of the analysis being conducted with novel variants that have not yet been previously described. Once these variants are classified using an integrated evaluation approach, they will be examined alongside other variants detected in the cohort that have previously been described but where the magnitude of their effect on the risk of sarcoma has not yet been defined. A case-control study will then be conducted, which will be seeking to establish whether these variants are found at a higher frequency in sarcoma patients than the general population, thus implying an association with sarcoma. Based on this information, these variants will then be graded according to the guidelines recommended by the IARC Unclassified Genetic Variants Working Group to guide clinical management for the different variants.

Myopathy in a woman and her daughter associated with a novel splice site MTM1 mutation

We have investigated a woman and her daughter with an early onset, slowly progressive myopathy. Muscle biopsy showed in both cases severe atrophy with marked fatty replacement. Frequent fibers with internalized nuclei were present but no typical features of centronuclear myopathy. There were also many fibers with deep invaginations of the plasma membrane. The presence of necklace fibers provided clue to correct genetic diagnosis. Both patients had a novel heterozygous splice site mutation in the myotubularin gene, MTM1 (c.867+1G>T). Analysis of MTM1 cDNA revealed that the mutation resulted in aberrant splicing with variable exon skipping. The expression of normal transcripts was markedly reduced and there was reduced expression of myotubularin protein. Although the expression of the allele without the mutation was reduced we did not obtain evidence of skewed X-chromosome inactivation. Other factors than skewed X-inactivation may cause allele inactivation and manifestation of severe myopathy in heterozygous carriers of pathogenic MTM1 mutations.

Association of LRRK2 exonic variants with susceptibility to Parkinson's disease: a case–control study

Background The leucine-rich repeat kinase 2 gene (LRRK2) harbours highly penetrant mutations that are linked to familial parkinsonism. However, the extent of its polymorphic variability in relation to risk of Parkinson's disease (PD) has not been assessed systematically. We therefore assessed the frequency of LRRK2 exonic variants in individuals with and without PD, to investigate the role of the variants in PD susceptibility. LRRK2 was genotyped in patients with PD and controls from three series (white, Asian, and Arab-Berber) from sites participating in the Genetic Epidemiology of Parkinson's Disease Consortium. Genotyping was done for exonic variants of LRRK2 that were identified through searches of literature and the personal communications of consortium members. Associations with PD were assessed by use of logistic regression models. For variants that had a minor allele frequency of 0·5% or greater, single variant associations were assessed, whereas for rarer variants information was collapsed across variants. 121 exonic LRRK2 variants were assessed in 15 540 individuals: 6995 white patients with PD and 5595 controls, 1376 Asian patients and 962 controls, and 240 Arab-Berber patients and 372 controls. After exclusion of carriers of known pathogenic mutations, new independent risk associations were identified for polymorphic variants in white individuals (M1646T, odds ratio 1·43, 95% CI 1·15-1·78; p=0·0012) and Asian individuals (A419V, 2·27, 1·35-3·83; p=0·0011). A protective haplotype (N551K-R1398H-K1423K) was noted at a frequency greater than 5% in the white and Asian series, with a similar finding in the Arab-Berber series (combined odds ratio 0·82, 0·72-0·94; p=0·0043). Of the two previously reported Asian risk variants, G2385R was associated with disease (1·73, 1·20-2·49; p=0·0026), but no association was noted for R1628P (0·62, 0·36-1·07; p=0·087). In the Arab-Berber series, Y2189C showed potential evidence of risk association with PD (4·48, 1·33-15·09; p=0·012). The results for LRRK2 show that several rare and common genetic variants in the same gene can have independent effects on disease risk. LRRK2, and the pathway in which it functions, is important in the cause and pathogenesis of PD in a greater proportion of patients with this disease than previously believed. These results will help discriminate those patients who will benefit most from therapies targeted at LRRK2 pathogenic activity. Michael J Fox Foundation and National Institutes of Health.

Reduced penetrance of autosomal dominant hypercholesterolemia in a high percentage of families: Importance of genetic testing in the entire family

BackgroundAutosomal dominant hypercholesterolemias (ADHs) are characterised by increased plasma levels of total and LDL cholesterol, predisposing to premature atherosclerosis. ADHs comprise several diseases with undistinguishable phenotype, caused by mutations in different genes: LDLR, APOB and PCSK9. Genetic studies are usually performed in patients with altered cholesterol levels. However, some persons carrying pathogenic mutations are normocholesterolemic and there are no further studies about this subject. We have studied the frequency of families and individuals carrying ADH mutations who do not present the disease in Spanish population. MethodsWe have analysed genes known to cause ADH by direct sequencing in 24 ADH families (215 members). Functional effect of some LDLR gene mutations was assessed by transfecting cultured cells with plasmids. ResultsSix families with mutations presented 7 mutation carriers who did not show ADH phenotype: 30% of ADH families presented normocholesterolemic individuals, and 7% of carriers of pathogenic mutations did not show ADH phenotype. We have analysed the effect of some of these mutations and they are responsible for impaired LDL receptor function. We have excluded mutations in APOB and PCSK9 genes that could reduce LDLc levels. ConclusionsAn important percentage of ADH families presented individuals who do not show an ADH phenotype, but who are able to transmit the pathogenic mutation to their offspring. Genetic study of all subjects in ADH families should be performed in order to identify normocholesterolemic carriers that allow the detection of mutations in their descendants and the prevention of the disease consequences.