Natural History Study of Patients With MPS IIIA

Inclusion Criteria: * Documented MPS IIIA diagnosis * Children up to and including 9 years of age * The patient is sufficiently able, in the opinion of the Investigator, to adhere to the study visit schedule and other protocol requirements * The patient's parent(s) or legal guardian(s) has signed written informed consent, according to the local regulations and after all relevant aspects of the -study have been explained and discussed Exclusion Criteria: * The patient is participating in a clinical trial of any potential disease-modifying investigational medicinal product or taking high dose (\>100 mg/kg/day) synthetic genistein (patients on low dose or naturally derived genistein can be included in this study). * The patient has received a hematopoietic stem cell or bone marrow transplant or gene therapy. * The patient has received enzyme replacement therapy in the last 6 months. * Homozygous or compound heterozygous for the S298P mutation or the investigator and/or trial steering committee considers the patient not to have the classical severe form of MPS IIIA. * Individuals with rare and unrelated serious comorbidities e.g. Down syndrome, intraventricular hemorrhage in the new-born period, or extreme low birth weight (\<1500 grams). * Visual or hearing impairment sufficient, in the clinical judgment of the investigator, to preclude cooperation with neurodevelopmental testing. Use of hearing aids is permitted.