A Bayesian Analysis to Determine the Prevalence of Barth Syndrome in the Pediatric Population.

OBJECTIVE: To determine the prevalence of Barth syndrome in the pediatric population. STUDY DESIGN: Data were collected from the Barth Syndrome Foundation Registry and relevant literature. With the advent of genetic testing and whole-exome sequencing, a multipronged Bayesian analysis was used to estimate the prevalence of Barth syndrome based on published data on the incidence and prevalence of cardiomyopathy and neutropenia, and the respective subpopulations of patients with Barth syndrome indicated in these publications. RESULTS: Based on 7 published studies of cardiomyopathy and 2 published studies of neutropenia, the estimated prevalence of Barth syndrome is approximately 1 case per million male population. This contrasts with 99 cases in the Barth Syndrome Foundation Registry, 58 of which indicate a US location, and only 230-250 cases known worldwide. CONCLUSIONS: It appears that Barth syndrome is greatly underdiagnosed. There is a need for better education and awareness of this rare disease to move toward early diagnosis and treatment.

What's new in ankle fractures.

The diagnosis and treatment of ankle fractures has evolved considerably over the past two decades. Recent topics of interest have included indications for operative treatment of isolated lateral malleolus fractures, need for fixation of the posterior malleolus, utilization of the posterolateral approach, treatment of the syndesmosis, and the potential role of fibular nailing. In this update, we concisely review these topics and what to expect in the future literature.

The pharmacological chaperone AT2220 increases the specific activity and lysosomal delivery of mutant acid alpha-glucosidase, and promotes glycogen reduction in a transgenic mouse model of Pompe disease.

Pompe disease is an inherited lysosomal storage disorder that results from a deficiency in acid α-glucosidase (GAA) activity due to mutations in the GAA gene. Pompe disease is characterized by accumulation of lysosomal glycogen primarily in heart and skeletal muscles, which leads to progressive muscle weakness. We have shown previously that the small molecule pharmacological chaperone AT2220 (1-deoxynojirimycin hydrochloride, duvoglustat hydrochloride) binds and stabilizes wild-type as well as multiple mutant forms of GAA, and can lead to higher cellular levels of GAA. In this study, we examined the effect of AT2220 on mutant GAA, in vitro and in vivo, with a primary focus on the endoplasmic reticulum (ER)-retained P545L mutant form of human GAA (P545L GAA). AT2220 increased the specific activity of P545L GAA toward both natural (glycogen) and artificial substrates in vitro. Incubation with AT2220 also increased the ER export, lysosomal delivery, proteolytic processing, and stability of P545L GAA. In a new transgenic mouse model of Pompe disease that expresses human P545L on a Gaa knockout background (Tg/KO) and is characterized by reduced GAA activity and elevated glycogen levels in disease-relevant tissues, daily oral administration of AT2220 for 4 weeks resulted in significant and dose-dependent increases in mature lysosomal GAA isoforms and GAA activity in heart and skeletal muscles. Importantly, oral administration of AT2220 also resulted in significant glycogen reduction in disease-relevant tissues. Compared to daily administration, less-frequent AT2220 administration, including repeated cycles of 4 or 5 days with AT2220 followed by 3 or 2 days without drug, respectively, resulted in even greater glycogen reductions. Collectively, these data indicate that AT2220 increases the specific activity, trafficking, and lysosomal stability of P545L GAA, leads to increased levels of mature GAA in lysosomes, and promotes glycogen reduction in situ. As such, AT2220 may warrant further evaluation as a treatment for Pompe disease.

Barth syndrome.

First described in 1983, Barth syndrome (BTHS) is widely regarded as a rare X-linked genetic disease characterised by cardiomyopathy (CM), skeletal myopathy, growth delay, neutropenia and increased urinary excretion of 3-methylglutaconic acid (3-MGCA). Fewer than 200 living males are known worldwide, but evidence is accumulating that the disorder is substantially under-diagnosed. Clinical features include variable combinations of the following wide spectrum: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), endocardial fibroelastosis (EFE), left ventricular non-compaction (LVNC), ventricular arrhythmia, sudden cardiac death, prolonged QTc interval, delayed motor milestones, proximal myopathy, lethargy and fatigue, neutropenia (absent to severe; persistent, intermittent or perfectly cyclical), compensatory monocytosis, recurrent bacterial infection, hypoglycaemia, lactic acidosis, growth and pubertal delay, feeding problems, failure to thrive, episodic diarrhoea, characteristic facies, and X-linked family history. Historically regarded as a cardiac disease, BTHS is now considered a multi-system disorder which may be first seen by many different specialists or generalists. Phenotypic breadth and variability present a major challenge to the diagnostician: some children with BTHS have never been neutropenic, whereas others lack increased 3-MGCA and a minority has occult or absent CM. Furthermore, BTHS was first described in 2010 as an unrecognised cause of fetal death. Disabling mutations or deletions of the tafazzin (TAZ) gene, located at Xq28, cause the disorder by reducing remodeling of cardiolipin, a principal phospholipid of the inner mitochondrial membrane. A definitive biochemical test, based on detecting abnormal ratios of different cardiolipin species, was first described in 2008. Key areas of differential diagnosis include metabolic and viral cardiomyopathies, mitochondrial diseases, and many causes of neutropenia and recurrent male miscarriage and stillbirth. Cardiolipin testing and TAZ sequencing now provide relatively rapid diagnostic testing, both prospectively and retrospectively, from a range of fresh or stored tissues, blood or neonatal bloodspots. TAZ sequencing also allows female carrier detection and antenatal screening. Management of BTHS includes medical therapy of CM, cardiac transplantation (in 14% of patients), antibiotic prophylaxis and granulocyte colony-stimulating factor (G-CSF) therapy. Multidisciplinary teams/clinics are essential for minimising hospital attendances and allowing many more individuals with BTHS to live into adulthood.

Characterization of a transgenic short hairpin RNA-induced murine model of Tafazzin deficiency.

Barth's syndrome (BTHS) is an X-linked mitochondrial disease that is due to a mutation in the Tafazzin (TAZ) gene. Based on sequence homology, TAZ has been characterized as an acyltransferase involved in the metabolism of cardiolipin (CL), a unique phospholipid almost exclusively located in the mitochondrial inner membrane. Yeast, Drosophila, and zebrafish models have been invaluable in elucidating the role of TAZ in BTHS, but until recently a mammalian model to study the disease has been lacking. Based on in vitro evidence of RNA-mediated TAZ depletion, an inducible short hairpin RNA (shRNA)-mediated TAZ knockdown (TAZKD) mouse model has been developed (TaconicArtemis GmbH, Cologne, Germany), and herein we describe the assessment of this mouse line as a model of BTHS. Upon induction of the TAZ-specific shRNA in vivo, transgenic mouse TAZ mRNA levels were reduced by >89% in cardiac and skeletal muscle. TAZ deficiency led to the absence of tetralineoyl-CL and accumulation of monolyso-CL in cardiac muscle. Furthermore, mitochondrial morphology from cardiac and skeletal muscle was altered. Skeletal muscle mitochondria demonstrated disrupted cristae, and cardiac mitochondria were significantly enlarged and displace neighboring myofibrils. Physiological measurements demonstrated a reduction in isometric contractile strength of the soleus and a reduction in cardiac left ventricular ejection fraction of TAZKD mice compared with control animals. Therefore, the inducible TAZ-deficient model exhibits some of the molecular and clinical characteristics of BTHS patients and may ultimately help to improve our understanding of BTHS-related cardioskeletal myopathy as well as serve as an important tool in developing therapeutic strategies for BTHS.

Cardiac and skeletal muscle defects in a mouse model of human Barth syndrome.

Barth syndrome is an X-linked genetic disorder caused by mutations in the tafazzin (taz) gene and characterized by dilated cardiomyopathy, exercise intolerance, chronic fatigue, delayed growth, and neutropenia. Tafazzin is a mitochondrial transacylase required for cardiolipin remodeling. Although tafazzin function has been studied in non-mammalian model organisms, mammalian genetic loss of function approaches have not been used. We examined the consequences of tafazzin knockdown on sarcomeric mitochondria and cardiac function in mice. Tafazzin knockdown resulted in a dramatic decrease of tetralinoleoyl cardiolipin in cardiac and skeletal muscles and accumulation of monolysocardiolipins and cardiolipin molecular species with aberrant acyl groups. Electron microscopy revealed pathological changes in mitochondria, myofibrils, and mitochondrion-associated membranes in skeletal and cardiac muscles. Echocardiography and magnetic resonance imaging revealed severe cardiac abnormalities, including left ventricular dilation, left ventricular mass reduction, and depression of fractional shortening and ejection fraction in tafazzin-deficient mice. Tafazzin knockdown mice provide the first mammalian model system for Barth syndrome in which the pathophysiological relationships between altered content of mitochondrial phospholipids, ultrastructural abnormalities, myocardial and mitochondrial dysfunction, and clinical outcome can be completely investigated.

Loss of intestinal fatty acid binding protein increases the susceptibility of male mice to high fat diet-induced fatty liver.

Mice lacking I-FABP (encoded by the Fabp2 gene) exhibit a gender dimorphic response to a high fat/cholesterol diet challenge characterized by hepatomegaly in male I-FABP-deficient mice. In this study, we determined if this gender-specific modification of liver mass in mice lacking I-FABP is attributable to the high fat content of the diet alone and whether hepatic Fabp1 gene (encodes L-FABP) expression contributes to this difference. Wild-type and Fabp2-/- mice of both genders were fed a diet enriched with either polyunsaturated or saturated fatty acids (PUFA or SFA, respectively) in the absence of cholesterol. Male Fabp2-/- mice, but not female Fabp2-/- mice, exhibited increased liver mass and hepatic triacylglycerol (TG) deposition as compared to corresponding wild-type mice. In wild-type mice that were fed the standard chow diet, there was no difference in the concentration of hepatic L-FABP protein between males and females although the loss of I-FABP did cause a slight reduction of hepatic L-FABP abundance in both genders. The hepatic L-FABP mRNA abundance in both male and female wild-type and Fabp2-/- mice was higher in the PUFA-fed group than in the SFA-fed group, and was correlated with L-FABP protein abundance. No correlation between hepatic L-FABP protein abundance and hepatic TG concentration was found. The results obtained demonstrate that loss of I-FABP renders male mice sensitive to high fat diet-induced fatty liver, and this effect is independent of hepatic L-FABP.

Intracellular lipid binding proteins of the small intestine.

The small intestine contains three distinct proteins belonging to the intracellular lipid binding protein family: the liver-type fatty acid binding protein (L-FABP), the intestinal fatty acid binding protein (I-FABP) and the ileal lipid binding protein (ilbp). The function of these proteins in the small intestine has remained enigmatic. Targeted gene disruption studies may shed insights into the physiological importance of these proteins. In the case of I-FABP, this approach has demonstrated that the complete elimination of this protein in murine intestine does not compromise dietary fat absorption in vivo but is associated with the development of insulin resistance.