R. H. Lekanne Deprez

Two cases of severe neonatal hypertrophic cardiomyopathy caused by compound heterozygous mutations in the MYBPC3 gene

Background: Idiopathic (primary) hypertrophic cardiomyopathy (HCM) is mainly caused by mutations in genes encoding sarcomeric proteins. One of the most commonly mutated HCM genes is the myosin binding protein C (MYBPC3) gene. Mutations in this gene lead mainly to truncation of the protein which gives rise to a relatively mild phenotype. Pure HCM in neonates is rare and most of the time childhood HCM occurs in association with another underlying condition. Objective: To study the presence of mutations in the MYBPC3 gene in idiopathic childhood HCM. Methods:MYBPC3 coding region and splice junction variation were analysed by denaturing high performance liquid chromatography (DHPLC) and sequencing in DNA isolated from two neonates with severe unexplained HCM, who died within the first weeks of life. Results: Truncating mutations were found in both alleles of the MYBPC3 gene in both patients, suggesting there was no functional copy of the MYBPC3 protein. Patient 1 carried the maternally inherited c.2373_2374insG mutation and the paternally inherited splice-donor site mutation c.1624+1G→A. Patient 2 carried the maternally inherited frameshift mutation c.3288delA (p.Glu1096fsX92) and the paternally inherited non-sense mutation c.2827C→T (p.Arg943X). Conclusions: The findings indicate the need for mutation analysis of genes encoding sarcomeric proteins in childhood HCM and the possibility of compound heterozygosity.

A systematic review on screening for Fabry disease: prevalence of individuals with genetic variants of unknown significance

Screening for Fabry disease (FD) reveals a high prevalence of individuals with α-galactosidase A (GLA) genetic variants of unknown significance (GVUS). These individuals often do not express characteristic features of FD. A systematic review on FD screening studies was performed to interpret the significance of GLA gene variants and to calculate the prevalence of definite classical and uncertain cases. We searched PubMed and Embase for screening studies on FD. We collected data on screening methods, clinical, biochemical and genetic assessments. The pooled prevalence of identified subjects and those with a definite diagnosis of classical FD were calculated. As criteria for a definite diagnosis, we used the presence of a GLA variant, absent or near-absent leukocyte enzyme activity and characteristic features of FD. Fifty-one studies were selected, 45 in high-risk and 6 in newborn populations. The most often used screening method was an enzyme activity assay. Cut-off values comprised 10–55% of the mean reference value for men and up to 80% for women. Prevalence of GLA variants in newborns was 0.04%. In high-risk populations the overall prevalence of individuals with GLA variants was 0.62%, while the prevalence of a definite diagnosis of FD was 0.12%. The majority of identified individuals in high-risk and newborn populations harbour GVUS or neutral variants in the GLA gene. To determine the pathogenicity of a GVUS in an individual, improved diagnostic criteria are needed. We propose a diagnostic algorithm to approach the individual with an uncertain diagnosis.

Uncertain diagnosis of Fabry disease: Consensus recommendation on diagnosis in adults with left ventricular hypertrophy and genetic variants of unknown significance

BACKGROUND Screening in subjects with left ventricular hypertrophy (LVH) reveals a high prevalence of Fabry disease (FD). Often, a diagnosis is uncertain because characteristic clinical features are absent and genetic variants of unknown significance (GVUS) in the α-galactosidase A (GLA) gene are identified. This carries a risk of misdiagnosis, inappropriate counselling and extremely expensive treatment. We developed a diagnostic algorithm for adults with LVH (maximal wall thickness (MWT) of >12 mm), GLA GVUS and an uncertain diagnosis of FD. METHODS A Delphi method was used to reach a consensus between FD experts. We performed a systematic review selecting criteria on electrocardiogram, MRI and echocardiography to confirm or exclude FD. Criteria for a definite or uncertain diagnosis and a gold standard were defined. RESULTS A definite diagnosis of FD was defined as follows: a GLA mutation with ≤ 5% GLA activity (leucocytes, mean of reference value, males only) with ≥ 1 characteristic FD symptom or sign (neuropathic pain, cornea verticillata, angiokeratoma) or increased plasma (lyso)Gb3 (classical male range) or family members with definite FD. Subjects with LVH failing these criteria have a GVUS and an uncertain diagnosis. The gold standard was defined as characteristic storage in an endomyocardial biopsy on electron microscopy. Abnormally low voltages on ECG and severe LVH (MWT>15 mm) <20 years exclude FD. Other criteria were rejected due to insufficient evidence. CONCLUSIONS In adults with unexplained LVH and a GLA GVUS, severe LVH at young age and low voltages on ECG exclude FD. If absent, an endomyocardial biopsy with electron microscopy should be performed.

Early cerebral manifestations in a young female with Fabry disease with skewed X-inactivation.

To the Editor : Fabry disease (FD) is an X-linked lysosomal storage disorder caused by deficiency of the enzyme alpha-galactosidase A (αGal A). Accumulation of globotriaosylceramide (Gb3) in different cell types eventually leads to renal insufficiency, cardiomyopathy and central nervous system (CNS) involvement (1). CNS involvement is mainly characterized by white matter lesions (WMLs) and strokes (2, 3). Several cohort studies revealed that females with FD often do develop clinical manifestations, although the disease generally follows a milder course (4–7). WMLs and strokes have been reported in young males with FD (8–10), but not in young females. In this letter, we report the enzymatic, biochemical and molecular characteristics of a young female patient with FD who had signs of CNS involvement from the very early age of 13 years. The proband was the patient’s grandmother, diagnosed with FD after the evaluation of unexplained renal insufficiency. Patient’s aunt, mother and sister were subsequently also diagnosed with FD. The patient had several early signs and symptoms of FD: minor acroparesthesia during exercise, a few angiokeratoma on the trunk, cornea verticillata and bilateral high-frequency hearing loss. Renal and cardiac assessments were normal. Brain magnetic resonance imaging (MRI) at the age of 15 years showed a 4-mm periventricular WML on T2 and fluid-attenuated inversion recovery (FLAIR) images near the right posterior horn (Fig. 1a). In retrospect, this lesion was already present on the MRI performed at the age of 13 years. Intravenous enzyme replacement and antiplatelet therapy was started. One year later, a hemorrhagic infarction was present in the left globus pallidus (Fig. 1b) without any symptoms. Risk factors for cardiovascular disease only revealed a history of cigarette smoking. Fibrinogen, clotting factor VIII, antithrombin deficiency, lupus anticoagulant, factor II mutation, factor V Leiden mutation, protein (a) (b)

Recurrent and founder mutations in the Netherlands: mutation p.K217del in troponin T2, causing dilated cardiomyopathy.

Background. About 30% of dilated cardiomyopathy (DCM) cases are familial. Mutations are mostly found in the genes encoding lamin A/C, beta-myosin heavy chain and the sarcomeric protein cardiac troponin-T (TNNT2). Mutations in TNNT2 are reported in approximately 3% of DCM patients. The overall phenotype caused by TNNT2 mutations is thought to be a fully penetrant, severe disease. This also seems to be true for a recurrent deletion in the TNNT2 gene; p.K217del (also known as p.K210del). Methods. We compared the phenotype of all Dutch patients identified as carrying the TNNT2 p.K217del mutation with those described in the literature. All index patients underwent cardiological evaluation. Family screening was done in all described families. Results. Six DCM patients carrying the TNNT2 p.K217del mutation were identified from four Dutch families. Mean age of disease manifestation was 33 years. Heart transplantation was required in three of them at ages 12, 18 and 19 years. These outcomes are comparable with those described in the literature. Conclusion. Carriers of the TNNT2 p.K217del mutation in our Dutch families, as well as in families described in the literature before, generally show a severe, early-onset form of DCM. (Neth Heart J 2010;18:478-85.)

A novel lamin A/C mutation in a Dutch family with premature atherosclerosis

OBJECTIVE We report a novel lamin A/C (LMNA) mutation, p.Glu223Lys, in a family with extensive atherosclerosis, diabetes mellitus and steatosis hepatis. METHODS Sequence analysis of LMNA (using Alamut version 2.2), co-segregation analysis, electron microscopy, extensive phenotypic evaluation of the mutation carriers and literature comparison were used to determine the loss of function of this mutation. RESULTS The father of three siblings died at the age of 45 years. The three siblings and the brother and sister of the father were referred to the cardiovascular genetics department, because of the premature atherosclerosis and dysmorphic characteristics observed in the father at autopsy. The novel LMNA mutation, p.Glu223Lys, was identified in the proband and his two sons. Clinical evaluation revealed atherosclerosis, insulin resistance and hypertension in the proband and dyslipidemia and hepatic steatosis in all the patients with the mutation. CONCLUSION Based on the facts that in silico analysis predicts a possibly pathogenic mutation, the mutation co-segregates with the disease, only fibroblasts from mutation carriers show nuclear blebbing and a similar phenotype was reported to be due to missense mutations in LMNA we conclude that we deal with a pathogenic mutation. We conclude that the phenotype is similar to Dunnigan-type familial partial lipodystrophy.