TNNI3K mutation in familial syndrome of conduction system disease, atrial tachyarrhythmia and dilated cardiomyopathy.

Locus mapping has uncovered diverse etiologies for familial atrial fibrillation (AF), dilated cardiomyopathy (DCM), and mixed cardiac phenotype syndromes, yet the molecular basis for these disorders remains idiopathic in most cases. Whole-exome sequencing (WES) provides a powerful new tool for familial disease gene discovery. Here, synergistic application of these genomic strategies identified the pathogenic mutation in a familial syndrome of atrial tachyarrhythmia, conduction system disease (CSD), and DCM vulnerability. Seven members of a three-generation family exhibited the variably expressed phenotype, three of whom manifested CSD and clinically significant arrhythmia in childhood. Genome-wide linkage analysis mapped two equally plausible loci to chromosomes 1p3 and 13q12. Variants from WES of two affected cousins were filtered for rare, predicted-deleterious, positional variants, revealing an unreported heterozygous missense mutation disrupting the highly conserved kinase domain in TNNI3K. The G526D substitution in troponin I interacting kinase, with the most deleterious SIFT and Polyphen2 scores possible, resulted in abnormal peptide aggregation in vitro and in silico docking models predicted altered yet energetically favorable wild-type mutant dimerization. Ventricular tissue from a mutation carrier displayed histopathological hallmarks of DCM and reduced TNNI3K protein staining with unique amorphous nuclear and sarcoplasmic inclusions. In conclusion, mutation of TNNI3K, encoding a heart-specific kinase previously shown to modulate cardiac conduction and myocardial function in mice, underlies a familial syndrome of electrical and myopathic heart disease. The identified substitution causes a TNNI3K aggregation defect and protein deficiency, implicating a dominant-negative loss of function disease mechanism.

Prevalence and clinical manifestations of 22q11.2 microdeletion in adults with selected conotruncal anomalies.

OBJECTIVES: This study was designed to determine the prevalence and clinical manifestations of 22q11.2 microdeletion in adults with selected conotruncal anomalies and to assess the clinician's ability to predict the presence or absence of 22q11.2 microdeletion on the basis of clinical features. BACKGROUND: It is known that 22q11.2 microdeletion is a chromosomal anomaly with cardiac and extracardiac manifestations. The prevalence and manifestations in adults have not been well characterized. METHODS: A total of 103 consecutive adults with either tetralogy of Fallot (TOF), pulmonary atresia/ventricular septal defect (PA/VSD), or truncus arteriosus (TA) were prospectively screened for 22q11.2 microdeletion using a fluorescence in situ hybridization (FISH) assay. Clinicians were asked to predict 22q11.2 microdeletion status on the basis of clinical features. A geneticist blinded to FISH assay results reviewed photographs of the patients for typical dysmorphic features of 22q11.2 microdeletion. RESULTS: Six patients (prevalence 5.8%, 95% confidence interval 1.3 to 10.3) had 22q11.2 microdeletion (3 with TOF, 2 with PA/VSD, 1 with TA). In two of these patients, the clinician incorrectly predicted absence of the deletion. In three, typical dysmorphic features of 22q11.2 microdeletion were absent. CONCLUSIONS: Our work showed that 22q11.2 microdeletion is under-recognized in adults with congenital heart disease. The absence of typical phenotypic features makes it difficult to correctly predict if the deletion is present. Screening for 22q11.2 microdeletion should be considered in adults with high-risk cardiac lesions, as it has important implications in reproductive counseling and surveillance for associated extracardiac manifestations.

Genetic testing: practical, ethical, and counseling considerations.

Genetic testing is becoming a much more common practice in medicine today. This presents a unique set of challenges for medical professionals in virtually all specialties. The practical aspects of determining which test to order, and in interpreting the result accurately in the context of the family history, can be difficult. Additionally, the ethical conundrums that frequently present themselves when genetic risk assessment and/or genetic testing is being considered can be daunting. These challenges present real concerns for medical professionals and patients alike. Included in this article is a review of some of the practical and ethical complexities associated with genetic testing. Pretest and posttest genetic counseling is also emphasized as an important and essential process in today's medical practice.

Usual interstitial pneumonia complicating dyskeratosis congenita.

Dyskeratosis congenita (DC) is a rare disorder characterized by skin hyperpigmentation, nail dystrophy, and leukoplakia of mucous membranes. Pulmonary complications occur in approximately 20% of patients, although the specific histopathologic features, the temporal relationship between the diagnosis of DC and the development of pulmonary fibrosis, and the response to specific treatment are largely undefined. We describe 2 patients with DC who developed usual interstitial pneumonia. Pulmonary fibrosis developed 18 and 38 years after the original manifestations of DC. Both patients died of respiratory failure, 4 and 6 months after lung biopsy. Pulmonary fibrosis in patients with DC may be linked to underlying abnormalities of fibroblast function.

Sodium channel mutations and susceptibility to heart failure and atrial fibrillation.

CONTEXT: Dilated cardiomyopathy (DCM), a genetically heterogeneous disorder, causes heart failure and rhythm disturbances. The majority of identified DCM genes encode structural proteins of the contractile apparatus and cytoskeleton. Recently, genetic defects in calcium and potassium regulation have been discovered in patients with DCM, implicating an alternative disease mechanism. The full spectrum of genetic defects in DCM, however, has not been established. OBJECTIVES: To identify a novel gene for DCM at a previously mapped locus, define the spectrum of mutations in this gene within a DCM cohort, and determine the frequency of DCM among relatives inheriting a mutation in this gene. DESIGN, SETTING, AND PARTICIPANTS: Refined mapping of a DCM locus on chromosome 3p in a multigenerational family and mutation scanning in 156 unrelated probands with DCM, prospectively identified at the Mayo Clinic between 1987 and 2004. Relatives underwent screening echocardiography and electrocardiography and DNA sample procurement. MAIN OUTCOME MEASURE: Correlation of identified mutations with cardiac phenotype. RESULTS: Refined locus mapping revealed SCN5A, encoding the cardiac sodium channel, as a candidate gene. Mutation scans identified a missense mutation (D1275N) that cosegregated with an age-dependent, variably expressed phenotype of DCM, atrial fibrillation, impaired automaticity, and conduction delay. In the DCM cohort, additional missense (T220I, R814W, D1595H) and truncation (2550-2551insTG) SCN5A mutations, segregating with cardiac disease or arising de novo, were discovered in unrelated probands. Among individuals with an SCN5A mutation 27% had early features of DCM (mean age at diagnosis, 20.3 years), 38% had DCM (mean age at diagnosis, 47.9 years), and 43% had atrial fibrillation (mean age at diagnosis, 27.8 years). CONCLUSIONS: Heritable SCN5A defects are associated with susceptibility to early-onset DCM and atrial fibrillation. Similar or even identical mutations may lead to heart failure, arrhythmia, or both.

Pheochromocytomas and paragangliomas in von Hippel-Lindau disease: a role for laparoscopic and cortical-sparing surgery.

HYPOTHESIS: Von Hippel-Lindau disease (VHL) is an autosomal-dominant disorder characterized by benign and malignant tumors involving the central nervous system, kidneys, pancreas, adrenal glands, and paraganglia. Appropriate management of pheochromocytomas and paragangliomas in VHL is evolving as we better understand the genetics and natural course of the disease and master advanced surgical techniques for adrenalectomy. DESIGN: Retrospective chart review. SETTING: Tertiary referral center. PATIENTS: A total of 109 patients identified at the Mayo Clinic, Rochester, Minn, with VHL (60 males and 49 females) between January 1, 1975, and June 30, 2000. Seventeen patients (16%) had an identifiable adrenal mass and 3 patients had paragangliomas. Follow-up was complete in all but 2 patients. MAIN OUTCOME MEASURES: Clinical presentation, preoperative evaluation, surgical management, and outcome. RESULTS: Three patients with paragangliomas and 13 of 17 patients with adrenal masses underwent surgical resection. Median age at time of diagnosis was 30 years (range, 16-47 years); 8 (40%) were asymptomatic. Fractionated urinary catecholamine and metanephrine concentrations were normal in one third of patients. Computed tomographic scanning identified 20 (83%) of 24 tumors. Adrenalectomies were performed as unilateral or bilateral, open or laparoscopic, and, finally, total or cortical-sparing. Seven (50%) of the patients underwent other concurrent abdominal procedures. There were no deaths, with an overall operative morbidity of 2 patients (14%). Only the 2 patients in whom bilateral total adrenalectomies were performed became corticosteroid dependent. No recurrences have been noted to date. CONCLUSIONS: A multidisciplinary approach is imperative for proper examination and monitoring of patients with VHL. Evaluation should begin early in life and always before elective surgery and childbirth. All adrenal masses in patients with VHL should be thoroughly evaluated and most should be resected. Early intervention and advanced surgical techniques better allow for cortical-sparing and laparoscopic procedures. With low recurrence rates, corticosteroid independence can be maintained for prolonged periods.

Homozygosity mapping and exome sequencing reveal GATAD1 mutation in autosomal recessive dilated cardiomyopathy.

BACKGROUND: Dilated cardiomyopathy (DCM) is a heritable, genetically heterogeneous disorder that typically exhibits autosomal dominant inheritance. Genomic strategies enable discovery of novel, unsuspected molecular underpinnings of familial DCM. We performed genome-wide mapping and exome sequencing in a unique family wherein DCM segregated as an autosomal recessive (AR) trait. METHODS AND RESULTS: Echocardiography in 17 adult descendants of first cousins revealed DCM in 2 female siblings and idiopathic left ventricular enlargement in their brother. Genotyping and linkage analysis mapped an AR DCM locus to chromosome arm 7q21, which was validated and refined by high-density homozygosity mapping. Exome sequencing of the affected sisters was then used as a complementary strategy for mutation discovery. An iterative bioinformatics process was used to filter >40,000 genetic variants, revealing a single shared homozygous missense mutation localized to the 7q21 critical region. The mutation, absent in HapMap, 1000 Genomes, and 474 ethnically matched controls, altered a conserved residue of GATAD1, encoding GATA zinc finger domain-containing protein 1. Thirteen relatives were heterozygous mutation carriers with no evidence of myocardial disease, even at advanced ages. Immunohistochemistry demonstrated nuclear localization of GATAD1 in left ventricular myocytes, yet subcellular expression and nuclear morphology were aberrant in the proband. CONCLUSIONS: Linkage analysis and exome sequencing were used as synergistic genomic strategies to identify GATAD1 as a gene for AR DCM. GATAD1 binds to a histone modification site that regulates gene expression. Consistent with murine DCM caused by genetic disruption of histone deacetylases, the data implicate an inherited basis for epigenetic dysregulation in human heart failure.

Mutations in ribonucleic acid binding protein gene cause familial dilated cardiomyopathy.

OBJECTIVES: We sought to identify a novel gene for dilated cardiomyopathy (DCM). BACKGROUND: DCM is a heritable, genetically heterogeneous disorder that remains idiopathic in the majority of patients. Familial cases provide an opportunity to discover unsuspected molecular bases of DCM, enabling pre-clinical risk detection. METHODS: Two large families with autosomal-dominant DCM were studied. Genome-wide linkage analysis was used to identify a disease locus, followed by fine mapping and positional candidate gene sequencing. Mutation scanning was then performed in 278 unrelated subjects with idiopathic DCM, prospectively identified at the Mayo Clinic. RESULTS: Overlapping loci for DCM were independently mapped to chromosome 10q25-q26. Deoxyribonucleic acid sequencing of affected individuals in each family revealed distinct heterozygous missense mutations in exon 9 of RBM20, encoding ribonucleic acid (RNA) binding motif protein 20. Comprehensive coding sequence analyses identified missense mutations clustered within this same exon in 6 additional DCM families. Mutations segregated with DCM (peak composite logarithm of the odds score >11.49), were absent in 480 control samples, and altered residues within a highly conserved arginine/serine (RS)-rich region. Expression of RBM20 messenger RNA was confirmed in human heart tissue. CONCLUSIONS: Our findings establish RBM20 as a DCM gene and reveal a mutation hotspot in the RS domain. RBM20 is preferentially expressed in the heart and encodes motifs prototypical of spliceosome proteins that regulate alternative pre-messenger RNA splicing, thus implicating a functionally distinct gene in human cardiomyopathy. RBM20 mutations are associated with young age at diagnosis, end-stage heart failure, and high mortality.

Delineation of the cryptic 1qter deletion phenotype.

The 1qter microdeletion is often reported in the literature as a part of a complex chromosome rearrangement. We describe a patient with a normal initial cytogenetic analysis later found by subtelomeric FISH to have a de novo isolated 1qter microdeletion. Further characterization was completed through microarray comparative genomic hybridization (CGH) and specific bacterial artificial chromosomes (BACs) to a region of 5.2-5.3 Mbp. Six additional cases were reviewed from a literature search. While no particular feature is specifically unique, the most frequently associated features include short stature, developmental delay and mental retardation, microcephaly, seizures, abnormal corpus callosum, and abnormal ear shape. This further delineates the phenotype and further narrows the chromosomal region responsible for a 1qter microdeletion phenotype.

Mosaic ring 20 with no detectable deletion by FISH analysis: Characteristic seizure disorder and literature review.

Ring chromosome 20 is a rare chromosome disorder characterized by a typical seizure phenotype consisting of complex partial seizures, frequent progression to generalized tonic or tonic-clonic seizures, and nocturnal frontal lobe seizures with frequent episodes of non-convulsive status epilepticus. Development may be normal or mildly delayed, followed by cognitive and behavioral decline after seizure onset. Here, we describe a patient with a typical severe seizure phenotype and a mosaic ring chromosome 20 without loss of p or q subtelomere regions or telomeric sequences. The ring had a longer telomere length than either of the telomere ends of its homologous chromosome 20 by quantitative fluorescence in situ hybridization analysis, suggesting that it might be derived from telomere-telomere fusion. The phenotypic comparison of this patient and other chromosome 20 cases that had terminal deletions of 20qter (n = 1) and 20pter (n = 7), shows that the epilepsy phenotype and electroencephalographic abnormalities are characteristic in patients with ring chromosome 20. Several hypotheses have been proposed to address the elusive mechanisms underlying the seizure disorder in ring chromosome 20. These possibilities include haploinsufficiency of two epilepsy genes CHRNA4 and KCNQ2 located at 20qter, silencing of these genes by a telomere position effect, or microdeletions or rearrangements of genetic material during the ring formation.

Utility of subtelomeric fluorescent DNA probes for detection of chromosome anomalies in 425 patients.

PURPOSE: A complete set of subtelomeric fluorescent DNA probes, except the acrocentric p-arms, was developed in 1996, was optimized in 1998, and is commercially available. These and other fluorescence in situ hybridization (FISH) probes have been used to detect anomalies of the subtelomere regions among groups of patients with idiopathic mental retardation (MR), developmental delay (DD), and/or nonspecific dysmorphic features (NDF), and individuals with multiple miscarriages (MM) who were karyotypically normal by standard G-banding techniques. METHODS: A total of 425 patients were analyzed, of whom 372 had idiopathic MR/DD/NDF and 53 were involved in MM. An effort was made to select individuals for this study who were either normal karyotypically or who had subtle chromosomal anomalies that were inconclusive by banded chromosome analysis, although this was not always possible. RESULTS: Anomalies involving the subtelomere regions were detected at a frequency of 6.8% in the MR/DD/NDF group. The cryptic or subtle anomalies are estimated to be about 3.4%. It was necessary to use M-FISH, chromosome, and locus specific FISH probes to clarify some of the abnormalities. No abnormalities were detected in the MM group. Deletion variants were present for 2qter, 7pter, and Xpter/Ypter subtelomeric regions ranging from <1 to 9.6%. CONCLUSIONS: The subtelomeric FISH probes are instrumental in the detection of subtelomeric anomalies in a significant proportion, although no more than 50% are subtle, of patients with idiopathic MR/DD/NDF. In some cases, however, it was necessary to use other FISH probes to clarify the nature of these abnormalities. No subtelomeric abnormalities were detected in our group of 53 MM patients, suggesting a relatively low frequency of occurrence in this patient population.

Microduplication 22q11.2, an emerging syndrome: clinical, cytogenetic, and molecular analysis of thirteen patients.

Chromosome 22, particularly band 22q11.2, is predisposed to rearrangements due to misalignments of low-copy repeats (LCRs). DiGeorge/velocardiofacial syndrome (DG/VCFS) is a common disorder resulting from microdeletion within the same band. Although both deletion and duplication are expected to occur in equal proportions as reciprocal events caused by LCR-mediated rearrangements, very few microduplications have been identified. We have identified 13 cases of microduplication 22q11.2, primarily by interphase fluorescence in situ hybridization (FISH). The size of the duplications, determined by FISH probes from bacterial artificial chromosomes and P(1) artificial chromosomes, range from 3-4 Mb to 6 Mb, and the exchange points seem to involve an LCR. Molecular analysis based on 15 short tandem repeats confirmed the size of the duplications and indicated that at least 1 of 15 loci has three alleles present. The patients' phenotypes ranged from mild to severe, sharing a tendency for velopharyngeal insufficiency with DG/VCFS but having other distinctive characteristics, as well. Although the present series of patients was ascertained because of some overlapping features with DG/VCF syndromes, the microduplication of 22q11.2 appears to be a new syndrome.