Stratification of Fabry mutations in clinical practice: a closer look at α-galactosidase A-3D structure.

BACKGROUND: Fabry disease (FD) is an X-linked lysosomal storage and multi-system disorder due to mutations in the α-galactosidase A (α-GalA) gene. We investigated the impact of individual amino acid exchanges in the α-GalA 3D-structure on the clinical phenotype of FD patients. PATIENTS AND METHODS: We enrolled 80 adult FD patients with α-GalA missense mutations and stratified them into three groups based on the amino acid exchange location in the α-GalA 3D-structure: patients with active site mutations, buried mutations and other mutations. Patient subgroups were deep phenotyped for clinical and laboratory parameters and FD-specific treatment. RESULTS: Patients with active site or buried mutations showed a severe phenotype with multi-organ involvement and early disease manifestation. Patients with other mutations had a milder phenotype with less organ impairment and later disease onset. α-GalA activity was lower in patients with active site or buried mutations than in those with other mutations (P < 0.01 in men; P < 0.05 in women) whilst lyso-Gb3 levels were higher (P < 0.01 in men; <0.05 in women). CONCLUSIONS: The type of amino acid exchange location in the α-GalA 3D-structure determines disease severity and temporal course of symptom onset. Patient stratification using this parameter may become a useful tool in the management of FD patients.

Detection of blood Gb3 deposits as a new tool for diagnosis and therapy monitoring in patients with classic Fabry disease.

BACKGROUND: The X-linked Fabry disease (FD) is a multiorgan disorder due to alpha-galactosidase A (α-GAL) deficiency with consequent lysosomal accumulation of globotriaosylceramide (Gb3). We established the immunocytochemical detection of Gb3 in blood cells of FD patients as a new method for FD diagnostics, follow-up and treatment control. METHODS: We enrolled 67 FD patients (37 men, 30 women) and 52 healthy controls (26 men, 26 women). PBMC were isolated from whole venous blood and 3x105 cells were immunoreacted with antibodies against CD77 as a marker for Gb3. Using fluorescence microscopy, the mean percentage of Gb3 positive PBMC was determined by an investigator blinded to subject allocation. As a second method, we qualitatively assessed Gb3 positive cells in blood smears. RESULTS: Gb3 deposits were unequivocally visible in PBMC and in blood smears. Men (P < 0.001) and women (P < 0.01) with classical FD had more Gb3-positive PBMC than healthy controls, whose samples only occasionally showed positive cells. The number of Gb3 positive PBMC was negatively correlated with α-GAL activity and positively correlated with plasma lyso-Gb3 levels. Only the PBMC Gb3 load but not plasma lyso-Gb3 reflected short- and long-term effects of enzyme replacement therapy (P < 0.01). CONCLUSIONS: Gb3 can be visualized in PBMC and blood smears and can be used as a novel marker for diagnostics, follow-up and treatment control in FD.

Impact of immunosuppressive therapy on therapy-neutralizing antibodies in transplanted patients with Fabry disease.

BACKGROUND: Inhibitory antibodies towards enzyme replacement therapy (ERT) are associated with disease progression and poor outcome in affected male patients with lysosomal disorders such as Fabry disease (FD). However, little is known about the impact of immunosuppressive therapy on ERT inhibition in these patients with FD. METHODS: In this retrospective study, we investigated the effect of long-term immunosuppression on ERT inhibition in male patients with FD (n = 26) receiving immunosuppressive therapy due to kidney (n = 24) or heart (n = 2) transplantation. RESULTS: No ERT-naïve transplanted patient (n = 8) developed antibodies within follow-up (80 ±72 months) after ERT initiation. Seven (26.9%) patients were tested ERT inhibition positive prior to transplantation. No de novo ERT inhibition was observed after transplantation (n = 18). In patients treated with high dosages of immunosuppressive medication such as prednisolone, tacrolimus and mycophenolate-mofetil/mycophenolate acid, ERT inhibition decreased after transplantation (n = 12; P = 0.0160). Tapering of immunosuppression (especially prednisolone) seemed to re-increase ERT inhibition (n = 4, median [range]: 16.6 [6.9; 36.9] %; P = 0.0972) over time. One ERT inhibition-positive patient required interventions with steroid therapy and increased doses of tacrolimus, which also lowered ERT inhibition. CONCLUSION: We conclude that the immunosuppressive maintenance therapy after transplantations seems to be sufficient to prevent de novo ERT inhibition in ERT-naïve patients. Intensified high dosages of immunosuppressive drugs are associated with decreased antibody titres and decreased ERT inhibition in affected patients, but did not result in long-term protection. Future studies are needed to establish ERT inhibition-specific immunosuppressive protocols with long-term modulating properties to warrant an improved disease course in ERT inhibition-positive males.

MR safety: fast T1 thermometry of the RF-induced heating of medical devices.

Determining the MR compatibility of medical implants and devices is becoming increasingly relevant. In most cases, the heating of conductive implants due to radiefrequency (RF) excitation pulses is measured by fluoroptic temperature sensors in relevant tests for approval. Another common method to determine these heating effects is MR thermometry using the proton resonance frequency. This method gives good results in homogeneous phantoms. However in many cases, technical shortcomings such as susceptibility artifacts prohibit exact proton resonance frequency thermometry near medical implants. Therefore, this work aimed at developing a fast T1-based method which allows controlled MR-related heating of a medical implant while simultaneously quantifying the spatial and temporal temperature distribution. To this end, an inversion recovery snapshot Fast Low-Angle Shot (FLASH) sequence was modified with additional off-resonant heating pulses. With an accelerated imaging method and a sliding-window technique, every 7.6 s a new temperature map could be generated with a spatial in-plane resolution of 2 mm. The temperature deviation from calculated temperature values to reference fluoroptic probe was found to be smaller than 1 K.

Towards robust in vivo quantification of oscillating biomagnetic fields using Rotary Excitation based MRI.

Spin-lock based functional magnetic resonance imaging (fMRI) has the potential for direct spatially-resolved detection of neuronal activity and thus may represent an important step for basic research in neuroscience. In this work, the corresponding fundamental effect of Rotary EXcitation (REX) is investigated both in simulations as well as in phantom and in vivo experiments. An empirical law for predicting optimal spin-lock pulse durations for maximum magnetic field sensitivity was found. Experimental conditions were established that allow robust detection of ultra-weak magnetic field oscillations with simultaneous compensation of static field inhomogeneities. Furthermore, this work presents a novel concept for the emulation of brain activity utilizing the built-in MRI gradient system, which allows REX sequences to be validated in vivo under controlled and reproducible conditions. Via transmission of Rotary EXcitation (tREX), we successfully detected magnetic field oscillations in the lower nano-Tesla range in brain tissue. Moreover, tREX paves the way for the quantification of biomagnetic fields.

Description of a novel RyR2 mutation in a juvenile patient with symptomatic catecholaminergic polymorphic ventricular tachycardia in sleep and during exercise: a case report.

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia is an inherited disease presenting with arrhythmic events during physical exercise or emotional stress. If untreated, catecholaminergic polymorphic ventricular tachycardia is a highly lethal condition: About 80% of affected individuals experience recurrent syncope, and 30% experience cardiac arrest. Catecholaminergic polymorphic ventricular tachycardia is caused by mutations in genes encoding ryanodine receptor type 2 (RyR2) and cardiac calsequestrin (CASQ2). In cases of sympathoadrenergic activation, both mutations result in a spontaneous Ca2+ release in cardiac cells, facilitating ventricular arrhythmias. CASE PRESENTATION: We present a case of a 17-year-old Caucasian boy who survived sudden cardiac death caused by ventricular fibrillation while performing running exercise in a fitness center. The diagnostic workup included blood tests, coronary angiography, electrophysiological testing, and cardiac magnetic resonance imaging, but all results were normal. Because the patient's medical history included recurrent syncope during physical and emotional stress, we strongly suspected catecholaminergic polymorphic ventricular tachycardia as the underlying disease. Genetic screening was performed and confirmed the diagnosis, revealing a new heterozygous point mutation in the gene for RyR2, c.12520T>A (p.F4174 l, exon 90, RyR2 gene). The patient was discharged from our hospital after undergoing implantation of an implantable cardioverter defibrillator for secondary prevention. Shortly after implantation, the implantable cardioverter defibrillator terminated a sustaining ventricular tachycardia episode by antitachycardic pacing. This episode occurred early in the morning while the patient was asleep. CONCLUSIONS: We present a case of catecholaminergic polymorphic ventricular tachycardia associated with a novel single point mutation in the RyR2 gene, which, to the best of our knowledge, has not been described in the literature so far. Our patient experienced arrhythmic events under both resting conditions and physical activity, an uncommon finding in patients with catecholaminergic polymorphic ventricular tachycardia. This novel mutation may cause arrhythmias independent of sympathoadrenergic stimulation, but further evidence is needed to prove causality.

[Safety of cardiac pacemakers and implantable cardioverter-defibrillators in magnetic resonance imaging. Assessment of the aggregate function at 1.5 tesla]. / Sicherheit von Herzschrittmachern und implantierbaren Kardioverter-Defibrillatoren im Magnetresonanztomographen. Beurteilung der Aggregatfunktion bei 1,5 Tesla.

BACKGROUND AND OBJECTIVE: Magnetic resonance imaging (MRI) is increasingly used in patients, but it is contraindicated in those with cardiac pacemakers (CP) or implantable cardioverter defibrillators (ICD). This study examined circumstances in which potentially life-threatening arrhythmias may be triggered in patients with CP undergoing MRI and whether these problems can be avoided by reprogramming of these devices. METHODS: Eight CP and seven ICDs were investigated in a phantom at 1.5 tesla (experimental and imaging sequences). RESULTS: A decrease in battery voltage was found in four CP after MRI (indication for elective replacement). Additionally, three showed changes in programming (resets). Analogous changes did not appear in the tested ICDs, but periods of tachycardia were recorded in all types of devices during MRI depending on the pulse sequence employed. CONCLUSION: MRI-related electromagnetic fields as used in routine MRI can induce severe pacemaker device malfunctions. Device programming approaches are unreliable for prevention of patient hazards, as programming changes or resets are one of the primary malfunctions during MRI.