Metachromatic leukodystrophy (MLD) is an autosomal recessive metabolic disorder characterized by sulfatide accumulation. Especially the white matter of the brain and peripheral nerves are affected, resulting in neurological deterioration and premature death. An allogenic hematopoietic stem cell transplantation (HSCT) in pre- and early-symptomatic MLD patients can lead to stable brain functions and increased survival, but the peripheral neuropathy often worsens. The object of my PhD project is to investigate peripheral neuropathy in MLD patients and gain insights into the clinical impact, possible pathomechanisms and potential treatments that might improve patient care and counseling. Key results so far are the course of peripheral neuropathy in MLD patients over time based on nerve conduction and nerve ultrasound studies, and the identification of: MLD causing mutations that are associated with severe or very mild peripheral neuropathy; neurodegenerative biomarkers that are associated with disease phenotype and disease progression before and after HSCT; sulfatide isoforms that accumulate only in late-infantile MLD patients in whom peripheral neuropathy is severe; higher degree of systemic inflammation in late-infantile MLD patients; and a systematic review on peripheral neuropathy in MLD.