Tuberous Sclerosis Complex I: gene identification and characterisation

This thesis describes the identification and the characterisation of the gene involved in tuberous sclerosis complex (TSC) on chromosome 9 (TSCl). For tItis purpose we used the positional cloning approach, a strategy by which many other disease genes, including the TSC2 gene on chromosome 16, have been isolated in the past years. The identification of the TSCI gene has taken 10 years of search and involved the cloning of the entire 1.5 Mb candidate region. Tuberous sclerosis is characterised by the widespread development of distinctive tumours (hamartomas) in many different tissues, and a broad phenotypic spectnl1u which lllay often include disturbed mental function, renal problems and dermatological abnormalities. TSC has an estimated prevalence of 1/6000 and occurs when either one of the TSCI or TSC2 tumour suppressor genes is inactivated. Mutations in the TSCI and TSC2 genes cause a velY similar clinical phenotype, suggesting that both genes play a closely related role in a still undetenllined biological process. Evidence for linkage between TSC and markers on cluomosome 9q34 had already been found in 1987. A consensus TSCI interval was defined in 1994, spanning approximately 1.5 Mb of genontic DNA. Refining the critical interval in affected individuals proved to be difficult, because of conflicting recombinant data in TSC families

Characterization of the cytosolic tuberin-hamartin complex. Tuberin is a cytosolic chaperone for hamartin

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by a broad phenotypic spectrum that includes seizures, mental retardation, renal dysfunction and dermatological abnormalities. Mutations to either the TSC1 or TSC2 gene are responsible for the disease. The TSC1 gene encodes hamartin, a 130-kDa protein without significant homology to other known mammalian proteins. Analysis of the amino acid sequence of tuberin, the 200-kDa product of the TSC2 gene, identified a region with limited homology to GTPase-activating proteins. Previously, we demonstrated direct binding between tuberin and hamartin. Here we investigate this interaction in more detail. We show that the complex is predominantly cytosolic and may contain additional, as yet uncharacterized components alongside tuberin and hamartin. Furthermore, because oligomerization of the hamartin carboxyl-terminal coiled coil domain was inhibited by the presence of tuberin, we propose that tuberin acts as a chaperone, preventing hamartin self-aggregation

Impact of sex on timing and clinical outcome of septal myectomy for obstructive hypertrophic cardiomyopathy

Background: Sex disparities are common in hypertrophic cardiomyopathy (HCM). Previous research has shown that at time of myectomy, women are older, have greater impairment of diastolic function and more advanced cardiac remodeling. The clinical impact of these differences is unknown. Method: This study included 162 HCM patients (61% m

Mutational spectrum of the TSC1 gene in a cohort of 225 tuberous sclerosis complex patients: no evidence for genotype-phenotype correlation

Tuberous sclerosis complex is an inherited tumour suppressor syndrome, caused by a mutation in either the TSC1 o

FLNC missense variants in familial noncompaction cardiomyopathy

The majority of familial noncompaction cardiomyopathy (NCCM) is explained by pathogenic variants in the same sarcomeric genes that are associated with hypertrophic (HCM) and dilated (DCM) cardiomyopathy. Pathogenic variants in the filamin C gene (FLNC) have been linked to HCM and DCM. We expand the spectrum of FLNC related cardiomyopathies by presenting two families with likely pathogenic FLNC variants showing familial segregation of NCCM and concurrent coarctation of the aorta and/or mitral valve abnormalities

TGDS pathogenic variants cause Catel-Manzke syndrome without hyperphalangy

Catel-Manzke syndrome, also known as micrognathia-digital-syndrome, is a rare autosomal recessive disorder characterized by the combination of the two cardinal features Pierre-Robin sequence and bilateral hyperphalangy leading to ulnar clinodactyly (ulnar curvature of the phalanges) and radial deviation (radial angulation at the metacarpophalangeal joint) of the index finge

Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report

Background: Isobutyryl-CoA dehydrogenase (IBD) is a mitochondrial enzyme catalysing the third step in the degradation of the essential branched-chain amino acid valine and is encoded by ACAD8. ACAD8 mutations lead to isobutyryl-CoA dehydrogenase deficiency (IBDD), which is identified by increased C4-acylcarnitine levels. Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis. Methods: Here, we review all previously published IBDD patients and describe a girl diagnosed with IBDD who was presenting with autism as the main disease feature. Results: To assess whether a phenotype-genotype correlation exists that could explain the development or absence of clinical symptoms in IBDD, we compared CADD scores, in silico mutation predictions, LoF tolerance scores and C4-acylcarnitine levels between symptomatic and asymptomatic individuals. Statistical analysis of these parameters did not establish significant differences amongst both groups. Conclusion: As in our proband, tri

A Dutch MYH7 founder mutation, p.(Asn1918Lys), is associated with early onset cardiomyopathy and congenital heart defects

Background Mutations in the myosin heavy chain 7 (MYH7) gene commonly cause cardiomyopathy but are less frequently associated with congenital heart defects. Methods In th

Effect of body surface area and gender on wall thickness thresholds in hypertrophic cardiomyopathy

Background: Family screening for hypertrophic cardiomyopathy (HCM) is based on genetic testing and clinical evaluation (maximal left ventricular wall thickness (MWT) ≥15 mm, or ≥13 mm in first-degree relatives of HCM patients). The aim of this study was to assess the effect of gender and body size on diagnosis of HCM and prediction of clinical outcome. Methods: This study includes 199 genotype-positive subjects (age 44 ± 15 years, 50% men) referred for cardiac screening. Gender-specific reference values for MWT indexed by body surface area (BSA), height and weight were derived from 147 healthy controls. Predictive accuracy of each method for HCM-related events was assessed by comparing areas under the receiver operating characteristic curves (AUC). Results: Men had a higher absolute, but similar BSA- and weight-indexed MWT compared with women (14.0 ± 3.9 mm vs 11.5 ± 3.8 mm, p  0.05). Applying BSA- and weight-indexed cut-off values decreased HCM diagnoses in the study group (48% vs 42%; 48% vs 39%, both p < 0.05), reclassified subjects in the largest, lightest and heaviest tertiles (≥2.03 m2: 58% vs 45%; ≤70 kg: 37% vs 46%; ≥85 kg: 53% vs 25%, all p < 0.05) and improved predictive accuracy (AUC 0.76 [95% CI 0.69–0.82] vs 0.78 [0.72–0.85]; and vs 0.80 [0.74–0.87]; both p < 0.05). Conclusions: In genotype-positive subjects referred for family screening, differences in MWT across gender are mitigated after indexation by BSA or weight. Indexation decreases the prevalence of HCM, particularly in larger men, and improves the predictive accuracy for HCM-related events

Lack of evidence for a causal role of CALR3 in monogenic cardiomyopathy

The pathogenicity of previously published disease-associated genes and variants is sometimes questionable. Large-scale, population-based sequencing studies have uncovered numerous false assignments of pathogenicity. Misinterpretation of sequence variants may have serious implications for the patients and families involved, as genetic test results are increasingly being used in medical decision making. In this study, we assessed the role of the calreticulin-3 gene (CALR3) in cardiomyopathy. CALR3 has been included in several cardiomyopathy gene panels worldwide. Its inclusion is based on a single publication describing two missense variants in patients with hypertrophic cardiomyopathy. In our national cardiomyopathy cohort (n = 6154), we identified 17 unique, rare heterozygous CALR3 variants in 48 probands. Overall, our patient cohort contained a significantly higher number of rare CALR3 variants compared to the ExAC population (p = 0.0036). However, after removing a potential Dutch founder variant, no statistically significant difference was found (p = 0.89). In nine probands, the CALR3 variant was accompanied by a disease-causing variant in another, well-known cardiomyopathy gene. In three families, the CALR3 variant did not segregate with the disease. Furthermore, we could not demonstrate calreticulin-3 protein expression in myocardial tissues at various ages. On the basis of these findings, it seems highly questionable that variants in CALR3 are a monogenic cause of cardiomyopathy