Heather MacLeod

Altered chromosomal positioning, compaction, and gene expression with a lamin A/C gene mutation.

Background Lamins A and C, encoded by the LMNA gene, are filamentous proteins that form the core scaffold of the nuclear lamina. Dominant LMNA gene mutations cause multiple human diseases including cardiac and skeletal myopathies. The nuclear lamina is thought to regulate gene expression by its direct interaction with chromatin. LMNA gene mutations may mediate disease by disrupting normal gene expression. Methods/Findings To investigate the hypothesis that mutant lamin A/C changes the laminas ability to interact with chromatin, we studied gene misexpression resulting from the cardiomyopathic LMNA E161K mutation and correlated this with changes in chromosome positioning. We identified clusters of misexpressed genes and examined the nuclear positioning of two such genomic clusters, each harboring genes relevant to striated muscle disease including LMO7 and MBNL2. Both gene clusters were found to be more centrally positioned in LMNA-mutant nuclei. Additionally, these loci were less compacted. In LMNA mutant heart and fibroblasts, we found that chromosome 13 had a disproportionately high fraction of misexpressed genes. Using three-dimensional fluorescence in situ hybridization we found that the entire territory of chromosome 13 was displaced towards the center of the nucleus in LMNA mutant fibroblasts. Additional cardiomyopathic LMNA gene mutations were also shown to have abnormal positioning of chromosome 13, although in the opposite direction. Conclusions These data support a model in which LMNA mutations perturb the intranuclear positioning and compaction of chromosomal domains and provide a mechanism by which gene expression may be altered.

Lamin A/C truncation in dilated cardiomyopathy with conduction disease

BackgroundMutations in the gene encoding the nuclear membrane protein lamin A/C have been associated with at least 7 distinct diseases including autosomal dominant dilated cardiomyopathy with conduction system disease, autosomal dominant and recessive Emery Dreifuss Muscular Dystrophy, limb girdle muscular dystrophy type 1B, autosomal recessive type 2 Charcot Marie Tooth, mandibuloacral dysplasia, familial partial lipodystrophy and Hutchinson-Gilford progeria.MethodsWe used mutation detection to evaluate the lamin A/C gene in a 45 year-old woman with familial dilated cardiomyopathy and conduction system disease whose family has been well characterized for this phenotype [1].ResultsDNA from the proband was analyzed, and a novel 2 base-pair deletion c.908_909delCT in LMNA was identified.ConclusionsMutations in the gene encoding lamin A/C can lead to significant cardiac conduction system disease that can be successfully treated with pacemakers and/or defibrillators. Genetic screening can help assess risk for arrhythmia and need for device implantation.

Therapy Insight: cardiovascular complications associated with muscular dystrophies

The muscular dystrophies are commonly associated with cardiovascular complications, including cardiomyopathy and cardiac arrhythmias. These complications are caused by intrinsic defects in cardiomyocyte and cardiac conduction system function, and by the presence of severe skeletal muscle disease, which also contributes to cardiac dysfunction. Unlike the skeletal muscle degenerative process, for which treatment options are currently limited, therapy is available for the cardiovascular complications that accompany muscular dystrophy. New therapies for skeletal muscle degeneration are moving into clinical trials and, ultimately, into clinical practice. These therapies are expected to also improve the cardiac function, longevity and wellbeing of muscular dystrophy patients.

A novel FKRP mutation in congenital muscular dystrophy disrupts the dystrophin glycoprotein complex

Mutations in the gene encoding fukutin related protein (FKRP) produce a spectrum of disease including congenital muscular dystrophy and limb girdle muscular dystrophy. FKRP is one member of a class of molecules thought to be glycosyltransferases that mediate O-linked glycosylation. The primary target of these glycosyltransferases is thought to be dystroglycan. We now report two unrelated Mexican children with congenital muscular dystrophy who each have the identical, novel 1387A>G, N463D mutation. Muscle biopsies from these children show a reduction of alpha-dystroglycan and also show reduction of beta-dystroglycan, and alpha-, beta-, and gamma-sarcoglycan, suggesting that FKRP mutations can perturb membrane associated proteins beyond dystroglycan.

A Pilot Study of a Family History Risk Assessment Tool for Cardiovascular Disease

This study evaluated the effectiveness of using a family history questionnaire to ascertain patients and families at-risk for inherited cardiovascular disease. A questionnaire composed of 21 questions was developed based on the experience of a cardiovascular genetic counselor. This questionnaire was administered to 39 patients at a University-based cardiology practice reflecting general and specialized aspects of cardiovascular medicine. Using the number and degree of relatedness of relatives reported and limited age of onset information participants were ranked into three familial risk categories. Thirty-nine patients participated in this pilot study. Of the 39 patients, six Mendelian diseases were identified. All individuals surveyed in this study were found to be at high and/or moderate risk for at least one disease based on the family history questionnaire. Twenty-five out of 39 participants (64.1%) were found to be at high risk for at least one cardiovascular disease, and thirty-three out of 39 participants (84.6%) were found to be at moderate risk for at least one disease. A family history of arrhythmia disorders, hypertension, hyperlipidemia, coronary artery disease and diabetes were more likely to be associated with a personal history in family histories of both moderate and high risk. Family history questionnaires in cardiology clinics can be a cost-effective tool for identifying patients and families who are in the greatest need of genetic evaluation and genetic counseling services.

Ventricular fibrillation following autologous intramyocardial cell therapy for inherited cardiomyopathy

A 41-year-old male with cardiomyopathy from an inherited beta myosin heavy-chain mutation underwent treatment for heart failure with intramyocardial cell transplantation. He received direct injections into his heart of autologous precursor cells isolated from his blood. He immediately suffered ventricular fibrillation. Although he was resuscitated, he experienced a prolonged downward course that prohibited his undergoing transplantation. His autopsy revealed marked fibrosis throughout the myocardium with areas of mononuclear cell infiltrate. This case highlights the potential adverse effects associated with intramyocardial therapy in the cardiomyopathic heart.

Improving Forensic Pathologic Investigation of Sudden Death in the Young: Tools, Guidance, and Methods of Cardiovascular Dissection from the Sudden Death in the Young Case Registry

The Sudden Death in the Young (SDY) Case Registry, a prospective, population-based registry active in ten states, has developed tools to aid pathologists and death investigators in the evaluation and autopsy of unexplained, natural sudden deaths in the pediatric population. The tools were developed by a team of experts representing forensic pathology; pediatric-, cardiac-, and neuropathology; cardiology; neurology/epileptology; pediatrics; genetic counseling; and public health. These tools focus on collecting data relevant to determination of cause of death with a focus on dissection of the cardiovascular system. The tools provide an objective checklist format for ease of use and data extraction. By sharing the tools here and highlighting the examination of the cardiovascular system, the SDY Case Registry encourages a standardized approach to death investigation, autopsy, and data collection for sudden, unexpected deaths in the young towards a goal of informing prevention efforts. Acad Forensic Pathol. 2018 8(2): 347-391

Genetic Counselors’ Approach To Postmortem Genetic Testing After Sudden Death: An Exploratory Study

A significant portion of sudden death cases result from an underlying genetic etiology, which may be determined through postmortem genetic testing. The National Association of Medical Examiners (NAME) recommends that an appropriate postmortem sample is saved on all sudden death cases under the age of 40. Genetic counselors (GCs) play an important role in this process by working with medical examiners and coroners (ME/Cs) to recommend and interpret specific testing and to guide family members. A survey sent to the National Society of Genetic Counselors was designed and implemented to learn more about the experiences of genetic counselors who had considered or ordered postmortem genetic testing. Results showed that cardiovascular GCs were significantly more willing to recommend genetic testing in younger age decedents (ages 10, 18, 30, 40, and 50) compared to other specialty GCs (p<0.05, Chi-square). Thirty-seven percent (7 of 19) of GCs reported insurance covering some portion of genetic testing. Participants also reported highest success for DNA extractions with fresh and frozen blood, reinforcing NAME recommendations for appropriate sample collection for postmortem genetic testing. Overall, participating GCs demonstrated a very good understanding for the appropriate use of postmortem genetic testing and did identify suspected barriers of cost and lack of insurance coverage as deterrents. With the rapid decrease in costs for diagnostic genetic testing, ME/C awareness of NAME recommendations for sample collection and storage remain important to facilitate postmortem genetic testing.