Yuxin Fan

LAMP2 microdeletions in patients with Danon disease.

Background—Danon disease is an X-linked dominant disorder characterized by the clinical triad of hypertrophic cardiomyopathy, skeletal myopathy, and variable mental retardation. Pathologically, autophagic vacuoles are noted in both skeletal and cardiac muscle. It exhibits an X-linked dominant mode of inheritance, and male carriers are severely affected, whereas female carriers develop milder and later-onset cardiac symptoms. Danon disease has been associated with mutations in the lysosome-associated membrane glycoprotein 2 (LAMP2) gene located at Xq24, typically resulting in splicing defects or protein truncation affecting the LAMP2. Because of its rarity, the full spectrum of genetic mutation resulting in Danon disease has not been elucidated. Methods and Results—We analyzed 3 male cases with clinical and pathological findings consistent with Danon disease. Comprehensive mutational analysis failed to yield detectable products for selected LAMP2 exons, and genomic DNA deletion was suspected. Genomic junction fragment polymerase chain reaction analysis in case 1 identified a novel Alu-mediated 34-kb microdeletion encompassing the entire 5′-untranslated region and exon 1 of LAMP2. In case 2 and 3, junctional polymerase chain reaction and Southern blot analyses mapped the breakpoint to an MIRb and (TA)n simple repeats present in intron 3, which determined a 64-kb and a 58-kb deletion, respectively, thereby ablating exons 4 to 10. Western blot analysis confirmed the absence of LAMP2 in protein extract from lymphocytes of index case 2. Conclusion—This article is the first report of Danon disease caused by microdeletions at Xq24, which functionally ablate LAMP2. The microdeletion mechanism appears to involve 1 Alu-mediated unequal recombination and 2 chromosomal breakage points involving TA-rich repeat sequences.

Missense mutations in FBN1 exons 41 and 42 cause Weill–Marchesani syndrome with thoracic aortic disease and Marfan syndrome

Mutations in FBN1 cause a range of overlapping but distinct conditions including Marfan syndrome (MFS), Weill–Marchesani syndrome (WMS), familial thoracic aortic aneurysms/dissections (FTAAD), acromicric dysplasia (AD), and geleophysic dysplasia (GD). Two forms of acromelic dysplasia, AD and GD, characterized by short stature, brachydactyly, reduced joint mobility, and characteristic facies, result from heterozygous missense mutations occurring in exons 41 and 42 of FBN1; missense mutations in these exons have not been reported to cause MFS or other syndromes. Here we report on probands with MFS and WMS who have heterozygous FBN1 missense mutations in exons 41 and 42, respectively. The proband with WMS has ectopia lentis, short stature, thickened pinnae, tight skin, striae atrophicae, reduced extension of the elbows, contractures of the fingers and toes, and brachydactyly and has a missense mutation in exon 42 of FBN1 (c.5242T>C; p.C1748R). He also experienced a previously unreported complication of WMS, an acute thoracic aortic dissection. The second proband displays classic characteristics of MFS, including ectopia lentis, skeletal features, and aortic root dilatation, and has a missense mutation in exon 41 of FBN1 (c.5084G>A; p.C1695Y). These phenotypes provide evidence that missense mutations in exons 41 and 42 of FBN1 lead to MFS and WMS in addition to AD and GD and also suggest that all individuals with pathogenic FBN1 mutations in these exons should be assessed for thoracic aortic disease and ectopia lentis. Further studies are necessary to elucidate the factors responsible for the different phenotypes associated with missense mutations in these exons of FBN1.

Functional Changes in Pulmonary Arterial Endothelial Cells Associated with BMPR2 Mutations

Pulmonary arterial hypertension (PAH) is a devastating disease characterized by abnormal remodeling of small, peripheral pulmonary arteries. Germline mutations in the bone morphogenetic protein receptor type 2 (BMPR2) gene are a major risk factor for developing PAH. At present, the correlation between the BMPR2 mutation and the patients prognosis remains controversial despite several investigations. In this study, we explored the functional effects of four BMPR2 mutations to dissect the functional significance of the BMPR2 gene defect. Cellular immunofluorescence assay of four mutants (Tyr67Cys, Thr268fs, Ser863Asn, and Gln433X) revealed that the BMPR2 protein containing Thr268fs, Ser863Asn, or Gln433X exhibited abnormal subcellular localization. The BrdU incorporation and TUNEL assay suggested that any of the BMPR2 mutations Thr268fs, Ser863Asn, or Gln433X could improve endothelial cell apoptosis and decrease cell proliferation. All of the four mutants could inhibit nitric oxide (NO) synthesis in HLMVE cells, and ET-1 levels increased in the cells transfected with mutant Ser863Asn. Our results will improve the understanding of the genotype-phenotype correlations and mechanisms associated with BMPR2 mutations.

Hypertrophic cardiomyopathy: Can the noninvasive diagnostic testing identify high risk patients?

Hypertrophic cardiomyopathy (HCM) is the most common cause of sudden cardiac death (SCD) in the young, particularly among athletes. Identifying high risk individuals is very important for SCD prevention. The purpose of this review is to stress that noninvasive diagnostic testing is important for risk assessment. Extreme left ventricular hypertrophy and documented ventricular tachycardia and fibrillation increase the risk of SCD. Fragmented QRS and T wave inversion in multiple leads are more common in high risk patients. Cardiac magnetic resonance imaging provides complete visualization of the left ventricular chamber, allowing precise localization of the distribution of hypertrophy and measurement of wall thickness and cardiac mass. Moreover, with late gadolinium enhancement, patchy myocardial fibrosis within the area of hypertrophy can be detected, which is also helpful in risk stratification. Genetic testing is encouraged in all cases, especially in those with a family history of HCM and SCD.

A novel Alu-mediated Xq28 microdeletion ablates TAZ and partially deletes DNL1L in a patient with Barth syndrome.

A Novel Alu-Mediated Xq28 Microdeletion Ablates TAZ and Partially Deletes DNL1L in a Patient With Barth Syndrome Harinder R. Singh, Zhao Yang, Saad Siddiqui, Liana S. Pe~na, Brandy H. Westerfield, Yuxin Fan, Jeffrey A. Towbin, and Matteo Vatta* Children’s Hospital of Michigan, Division of Cardiology, The Carman and Ann Adams, Department of Pediatrics, Wayne State University School of Medicine, Detroit, Michigan Department of Pediatrics (Cardiology) and John Welsh Cardiovascular Diagnostic Laboratory, Baylor College of Medicine, Texas Children’s Hospital, Houston, Texas

Paucity of skeletal manifestations in hispanic families with FBN1 mutations

Marfan syndrome (MFS) is an autosomal dominant condition with pleiotropic manifestations involving the skeletal, ocular, and cardiovascular systems. The diagnosis is based primarily on clinical involvement of these and other systems, referred to as the Ghent criteria. We have identified three Hispanic families from Mexico with cardiovascular and ocular manifestations due to novel FBN1 mutations but with paucity of skeletal features. The largest family, hMFS001, had a frameshift mutation in exon 24 (3075delC) identified as the cause of aortic disease in the family. Assessment of eight affected adults revealed no major skeletal manifestation of MFS. Family hMFS002 had a missense mutation (R1530C) in exon 37. Four members fulfilled the criteria for ocular and cardiovascular phenotype but lacked skeletal manifestations. Family hMFS003 had two consecutive missense FBN1 mutations (C515W and R516G) in exon 12. Eight members fulfilled the ocular criteria for MFS and two members had major cardiovascular manifestations, however none of them met criteria for skeletal system. These data suggest that individuals of Hispanic descent with FBN1 mutations may not manifest skeletal features of the MFS to the same extent as Caucasians. We recommend that echocardiogram, ocular examination and FBN1 molecular testing be considered for any patients with possible MFS even in the absence of skeletal features, including Hispanic patients.

Interpreting Incidentally Identified Variants in Genes Associated With Catecholaminergic Polymorphic Ventricular Tachycardia in a Large Cohort of Clinical Whole-Exome Genetic Test Referrals

Background— The rapid expansion of genetic testing has led to increased utilization of clinical whole-exome sequencing (WES). Clinicians and genetic researchers are being faced with assessing risk of disease vulnerability from incidentally identified genetic variants which is typified by variants found in genes associated with sudden death-predisposing catecholaminergic polymorphic ventricular tachycardia (CPVT). We sought to determine whether incidentally identified variants in genes associated with CPVT from WES clinical testing represent disease-associated biomarkers. Methods and Results— CPVT-associated genes RYR2 and CASQ2 variants were identified in one of the world’s largest collections of clinical WES referral tests (N=6517, Baylor Miraca Genetics Laboratories) and compared with a control cohort of ostensibly healthy individuals (N=60 706) and a case cohort of CPVT cases (N=155). Within the WES cohort, the rate of rare variants in CPVT-associated genes was 8.8% compared with 6.0% among controls and 60.0% among cases. There was a predominance of variants of undetermined significance (97.7%). After protein topology mapping, WES variants colocalized more frequently to residues with variants found in controls compared with cases. Retrospective clinical evaluation of individuals referred to our institution with WES-positive variants demonstrated no evidence of clinical CPVT in individuals with a low pretest clinical suspicion for CPVT. Conclusions— The prevalence of incidentally identified CPVT-associated variants is ≈9% among WES tests. Variants of undetermined significances in CPVT-associated genes in WES genetic testing, in the absence of clinical suspicion for CPVT, are unlikely to represent markers of CPVT pathogenicity.

A Novel Exonic Splicing Mutation in the TAZ (G4.5) Gene in a Case with Atypical Barth Syndrome.

OBJECTIVE Barth syndrome is an X-linked recessive disorder characterized by dilated cardiomyopathy, neutropenia, 3-methylglutaconic aciduria, abnormal mitochondria, variably expressed skeletal myopathy, and growth delay. The disorder is caused by mutations in the tafazzin (TAZ/G4.5) gene located on Xq28. We report a novel exonic splicing mutation in the TAZ gene in a patient with atypical Barth syndrome. PATIENT & METHODS The 4-month-old proband presented with respiratory distress, neutropenia, and dilated cardiomyopathy with reduced ejection fraction of 10%. No 3-methylglutaconic aciduria was detected on repeated urine organic acid analyses. Family history indicated that his maternal uncle died of endocardial fibroelastosis and dilated cardiomyopathy at 26 months. TAZ DNA sequencing, mRNA analysis, and cardiolipin analysis were performed. RESULTS A novel nucleotide substitution c.553A>G in exon 7 of the TAZ gene was identified in the proband, predicting an amino acid substitution p.Met185Val. However, this mutation created a new splice donor signal within exon 7 causing mis-splicing of the message, producing two messages that only differ in the presence/absence of exon 5; these retain intron 6 and have only 11 bases of exon 7. Cardiolipin analysis confirmed the loss of tafazzin activity. The probands mother, maternal aunt, and grandmother carry the same mutation. CONCLUSIONS The identification of a TAZ gene mutation, mRNA analysis, and monolysocardiolipin/cardiolipin ratio determination were important for the diagnosis and genetic counseling in this family with atypical Barth syndrome that was not found to be associated with 3-methylglutaconic aciduria.

Heritable Thoracic Aortic Disease Genes in Sporadic Aortic Dissection

An acute aortic dissection is a life-threatening cardiovascular condition that is preventable if individuals at risk are identified. Pathogenic variants in 11 genes confer a highly penetrant, dominantly inherited risk for aortic aneurysms and dissections with or without syndromic features (e.g.,

FUNCTIONAL CHARACTERIZATION OF KCNJ2 MISSENSE VARIANTS IDENTIFIED IN PATIENTS WITH ANDERSEN-TAWIL SYNDROME

Andersen-Tawil syndrome (ATS), also called Long QT syndrome 7, is a rare autosomal dominant genetic disorder characterized by a triad of episodic flaccid muscle weakness, ventricular arrhythmias and prolonged QT interval, and anomalies such as low-set ears, ocular hypertelorism, small mandible,