Sulfamethoxazole for the Treatment of Primary PREPL Deficiency

Inclusion Criteria: * patients with molecular confirmation of primary PREPL deficiency * who are able to follow the study protocol (for the primary endpoint) * who have given written informed consent Exclusion Criteria: * age\<2m * women of child-bearing age unless using a reliable method for contraception and not pregnant at study entrance * additional diagnosis with influence on muscle force * not able to follow the study protocol (for the primary endpoint) * history of sulfonamide hypersensitivity * diminished renal function based on serum creatinine * transaminases higher than 3 times the upper limit of normal * for the pupillometry: eye pathology with the exception of refractive errors, drugs with influence on the pupillary light reflex