Lysosomal storage diseases are caused by mutated genes that express defective lysosomal proteins, such as essential enzymes. For example, cystinosis is a metabolic disease caused by a defective gene that encodes cystinosin, an exporter protein (Figure 1). Avrobio develops gene therapies to treat lysosomal storage diseases. On 8 October 2019, the company announced that its first patient had been dosed in the AVR-RD-04 investigational gene therapy program, which involves genetic modification of the patient’s own hematopoietic stem cells to treat cystinosis.…