PMC3669303_01
ECGs (25 mm/s, 5 mm/mV) of the proband at age 19.. (A) Resting ECG shows sinus bradycardia, ventricular preexcitation and significant left ventrical hypertrophy. (B) Irregularity of the rhythm, rapid ventricular response, delta waves, and wide, bizarre QRS complexes with beat-to-beat variations in configuration, strongly suggesting the diagnosis of combined AF and WPW. (C) Regular wide QRS complex tachycardia, most likely due to antidromic atrioventricular reentry tachycardia (AVRT), suggesting that the accessory connection is capable of sustaining reentry and participating in reciprocating tachycardias.
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The resting ECG at admission showed sinus bradycardia (50 bpm), ventricular preexcitation and significant LVH (Figure 1A). He experienced episodes of AF with ventricular rates up to 214 bpm (Figure 1B) and antidromic atrioventricular reentry tachycardia (AVRT) with a rate of 167 bpm (Figure 1C). The QRS morphology during sinus bradycardia, AF and AVRT was similar (Figure 1), suggesting antegrade conduction via the accessory pathway with variable ventricular pre-excitation.
The parasternal long-axis view (A) and short-axis view (B) of an echocardiogram of the proband.. It demonstrates severe concentric left ventricular (LV) hypertrophy with enlarged left chambers. AO, aorta; IVS, interventricular septum; LA, left atrium; LVPW: left ventricular posterior wall.
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Echocardiography revealed marked concentric LVH (septal thickness of 31 mm and posterior wall thickness of 32 mm) without signs of resting left ventricular outflow tract obstruction, an enlarged left atrium (diameter, 45 mm) and left ventricle (end-diastolic diameter, 65 mm), a left ventricular ejection fraction of 46% with mild left ventricular wall diffused hypokinesia and a small pericardial effusion (Figure 2).
Postero-anterior chest radiograph of the proband after permanent pacemaker implantation.. It shows severe cardiomegaly with a cardiothoracic rate of 70.6%.
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The chest X-ray showed severe cardiac enlargement with a cardiothoracic rate over 70% (Figure 3).
Histopathology of ventricular sections obtained from the proband.. (A) Cross section of ventricular myocardium shows hypertrophied myocytes with profound intracellular vacuolation and marked variation in the nucleus size (hematoxylin and eosin staining, original magnification x 400). (B) Myocardial fibers in longitudinal section shows loss of the normal parallel arrangement, increased side-branching, and frequent side-to-side branches connections (hematoxylin and eosin staining, original magnification x 400). (C) Masson's trichrome staining shows increased interstitial fibrosis with blue color (original magnification x 400). (D) Electron microscopy shows angulated myofibrillar with length-heterogeneity sarcomere lengths and excess mitochondria (bar = 5 microm). (E) Granular glycogen accumulation in the subsarcolemmal regions of cardiac myocytes (bar = 0.5 microm). (F) Myofibrillar dissolution and widening of intermyofibrillar spaces in which scattered glycogen granules and mitochondria are seen (bar = 2 microm). G, Prominent interstitial fibrosis and myofibrillar disarray (bar = 2 microm).
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Light microscopy evaluation of the proband's heart tissue obtained by biopsy revealed marked enlargement of myocytes with profound intracellular vacuolation, pleomorphism of nuclei (Figure 4A), loss of the normal parallel arrangement, frequent side-to-side connections (Figure 4B), and increased interstitial fibrosis (Figure 4C). Electron microscopy confirmed significant loss of myofibrils and myofibrillar disarray (Figure 4D). Markedly increased glycogen content was found in the interfibrillar, perinuclear and subsarcolemmal regions of cardiac myocytes (Figure 4E). There were no obvious mitochondrial morphological changes, but the number of mitochondria increased significantly, and clustered mitochondria showed the characteristic of regional accumulation (Figure 4D). In minority cells, there were irregular empty areas between myofibrils with the presence of scattered glycogen and mitochondria, which may be due to dissolution of glycogen (Figure 4F). Interstitial fibrosis was prominent and highly aggregated in partial areas (Figure 4G).
Genetic analysis identified a novel de novo PRKAG2 mutation.. (A) Family pedigree of the PRKAG2 mutant carrier. Arrow denotes proband. (B) DNA chromatogram shows a heterozygous A-to-G transition at nucleotide 1453 of PRKAG2, predicting a substitution of a glutamic acid for lysine at residue 485 (p.Lys485Glu) of the AMP-activated protein kinase (AMPK) gamma-2 subunit (K485E). (C) Amino acid alignments show that a lysine at position 485 is highly conserved among species. (D) Schematic of AMPK gamma-2 subunit and all PRKAG2 mutations discovered by far. Residue K485 is located at the linker between the third CBS domain and the fourth CBS domain.
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Genetic screening of the patient revealed a novel heterozygous mutation consisting of an A-to-G transition at nucleotide 1453 (c.1453A>G) in PRKAG2 predicting a substitution of a glutamic acid for lysine at residue 485 (p.Lys485Glu, K485E) of the AMPK gamma2 subunit (K485E, Figure 5B). This mutation was also absent in all family members, who were all negative for the syndrome (Figure 5A). Alignment of the amino acid sequence of the gamma2 subunit proteins showed that lysine at position 485 is highly conserved among species (Figure 5C). Residue K485 is located at the linker between the third and forth CBS domain (Figure 5D).
Electrostatic surfaces of (A) WT AMPK and (B) the K485E mutant.. Positively- and negatively-charged regions on the surface of the protein are shown in red and blue, respectively. The alpha, beta, and gamma subunits of the protein are colored in yellow, blue, and gray cartoons, respectively. The four CBS domains of the protein are also labeled for reference. The D248 and K485 residues are shown in ball-and-stick representation and labeled with arrows and insets provide a close-up look at the effect of the mutation on the salt bridge.
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Mutation of the lysine to a glutamate results in this positively-charged surface being replaced by a negatively-charged surface, which will repel the negative aspartate (Figure 6).