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Most paediatricians are familiar with the terms lysosomal storage disorders (LSDs) and neuromuscular disorders (NMDs), and these disease entities seem to have little in common. Here, I am giving a synopsis of autophagic vacuolar myopathies (AVMs), a relatively new group of diseases at the interface between LSDs and NMDs.1 2 AVMs (lysosomal myopathies) are characterised by the accumulation of abnormal lysosomes in muscle fibres resulting in specific clinical signs and symptoms.
The term “autophagy” is derived from the Greek words “autos” and “phago” meaning “self-eating”. Autophagy takes place in the lysosomes and refers to the process of breaking down cellular components and expelling the products back into the cytoplasm. Over the last few years this phenomenon has increasingly attracted the attention of scientists and doctors as it also has implications for ageing, cancer, infection, cardiovascular disease and neurodegenerative disease.3
LYSOSOMAL STORAGE DISORDERS
LSDs are a group of approximately 50 predominantly autosomal recessive diseases caused by a malfunctioning lysosomal protein. The defective protein can be a lysosomal enzyme, a lysosomal transporter or a membrane protein, which leads to accumulation of biological substrates and cell dysfunction. Central nervous system, skeleton, liver and spleen are frequently involved. The combined prevalence of LSDs is 1 in 7700.4 5 Enzyme assays are currently the gold standard for diagnostic testing. Several successful strategies have been developed to treat patients with specific lysosomal storage diseases. Allogeneic bone marrow transplantation has been used, among others, in mucopolysaccharidosis (MPS) types I and II. Intravenous enzyme replacement therapy (ERT) is available for MPS I and IV, Gaucher disease type I (GD I), Fabry disease and Pompe disease. More recently, substrate inhibition therapy with miglustat has been approved for GD I and Niemann-Pick disease type C (NPC). LSDs with central nervous system involvement pose a particular challenge due to difficulties in …