Pompe disease is an autosomal recessive glycogen storage disorder caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). GAA deficiency results in systemic lysosomal glycogen accumulation and cellular disruption in muscle and the central nervous system (CNS). Adeno-associated virus (AAV) gene therapy is ideal for Pompe disease, since a single systemic injection may correct both muscle and CNS pathologies. Using the Pompe mouse (B6;129-Gaa/J), this study sought to explore if AAVB1, a newly engineered vector with a high affinity for muscle and CNS, reduces systemic weakness and improves survival in adult mice. Three-month-old Gaa animals were injected with either AAVB1 or AAV9 vectors expressing GAA and tissues were harvested 6 months later. Both AAV vectors prolonged survival. AAVB1-treated animals had a robust weight gain compared to the AAV9-treated group. Vector genome levels, GAA enzyme activity, and histological analysis indicated that both vectors transduced the heart efficiently, leading to glycogen clearance, and transduced the diaphragm and CNS at comparable levels. AAVB1-treated mice had higher GAA activity and greater glycogen clearance in the tongue. Finally, AAVB1-treated animals showed improved respiratory function comparable to wild-type animals. In conclusion, AAVB1-GAA offers a promising therapeutic option for the treatment of muscle and CNS in Pompe disease.

Pompe disease is a neuromuscular disease caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase leading to lysosomal and cytoplasmic glycogen accumulation in neurons and striated muscle. In the decade since availability of first-generation enzyme replacement therapy (ERT) a better understanding of the clinical spectrum of disease has emerged. The most severe form of early onset disease is typically identified with symptoms in the first year of life, known as infantile-onset Pompe disease (IOPD). Infants are described at floppy babies with cardiac hypertrophy in the first few months of life. A milder form with late onset (LOPD) of symptoms is mostly free of cardiac involvement with slower rate of progression. Glycogen accumulation in the CNS and skeletal muscle is observed in both IOPD and LOPD.In both circumstances, multi-system disease (principally motoneuron and myopathy) leads to progressive weakness with associated respiratory and feeding difficulty. In IOPD the untreated natural history leads to cardiorespiratory failure and death in the first year of life. In the current era of ERT clinical outcomes are improved, yet, many patients have an incomplete response and a substantial unmet need remains. Since the neurological manifestations of the disease are not amenable to peripheral enzyme replacement, we set out to better understand the pathophysiology and potential for treatment of disease manifestations using adenoassociated virus (AAV)-mediated gene transfer, with the first clinical gene therapy studies initiated by our group in 2006. This review focuses on the preclinical studies and clinical study findings which are pertinent to the development of a comprehensive gene therapy strategy for both IOPD and LOPD. Given the advent of newborn screening, a significant focus of our recent work has been to establish the basis for repeat administration of AAV vectors to enhance neuromuscular therapeutic efficacy over the life span.

Pompe disease (OMIM 232300) is an autosomal recessive disorder caused by mutations in the gene encoding acid α-glucosidase (GAA) (EC 3.2.1.20), the enzyme responsible for hydrolyzing lysosomal glycogen. The primary cellular pathology is lysosomal glycogen accumulation in cardiac muscle, skeletal muscle, and motor neurons, which ultimately results in cardiorespiratory failure. However, the severity of pathology and its impact on clinical outcomes are poorly described in smooth muscle. The advent of enzyme replacement therapy (ERT) in 2006 has improved clinical outcomes in infantile-onset Pompe disease patients. Although ERT increases patient life expectancy and ventilator free survival, it is not entirely curative. Persistent motor neuron pathology and weakness of respiratory muscles, including airway smooth muscles, contribute to the need for mechanical ventilation by some patients on ERT. Some patients on ERT continue to experience life-threatening pathology to vascular smooth muscle, such as aneurysms or dissections within the aorta and cerebral arteries. Better characterization of the disease impact on smooth muscle will inform treatment development and help anticipate later complications. This review summarizes the published knowledge of smooth muscle pathology associated with Pompe disease in animal models and in patients.

Adeno-associated virus (AAV) serotype 9, which is under development for gene-delivery applications, shows significantly enhanced capsid-associated transduction efficiency in muscle compared with other AAV serotypes. With the aim of characterizing the structural determinants of this property, the purification, crystallization and preliminary X-ray crystallographic analyses of the AAV9 viral capsid are reported. The crystals diffracted X-rays to 2.8 Å resolution using synchrotron radiation and belonged to the trigonal space group P3 2 , with unit-cell parameters a = b = 251.0, c = 640.0 Å . There are three complete viral capsids in the crystal unit cell. The orientation and position of the asymmetric unit capsid have been determined by molecular-replacement methods and structure determination is in progress.

Pompe disease is caused by the deficiency of lysosomal acid α-glucosidase (GAA). It is expected that gene therapy to replace GAA with adeno-associated virus (AAV) vectors will be less effective early in life because of the rapid loss of vector genomes. AAV2/8-LSPhGAA (3 × 1010 vector genomes [vg]/mouse) was administered to infant (2-week-old) or adult (2-month-old) GAA knockout mice. AAV vector transduction in adult mice significantly corrected GAA deficiency in the heart (p < 0.0001), diaphragm (p < 0.01), and quadriceps (p < 0.001) for >50 weeks. However, in infant mice, the same treatment only partially corrected GAA deficiency in the heart (p < 0.05), diaphragm (p < 0.05), and quadriceps (p < 0.05). The clearance of glycogen was much more efficient in adult mice compared with infant mice. Improved wire hang test latency was observed for treated adults (p < 0.05), but not for infant mice. Abnormal ventilation was corrected in both infant and adult mice. Vector-treated female mice demonstrated functional improvement, despite a lower degree of biochemical correction compared with male mice. The relative vector dose for infants was approximately 3-fold higher than adults, when normalized to body weight at the time of vector administration. Given these data, the dose requirement to achieve similar efficacy will be higher for the treatment of young patients.