Background: Mucopolysaccharidosis (MPSs) are group of metabolic disorders belong to large family of lysosomal disorders. MPSs disorders caused by genetic changes that lead to deficiency, absence or malfunctions of specific lysosomal enzymes are required to break down glycosaminoglycans (GAGs). Overtime, accumulation of (GAGs) in various body tissues results in permanent progressive damage affecting appearance, physical abilities and systemic function including mental development. MPS type IV (OMIM 612222) also called (Morquio syndrome) characterized by sever skeletal and bone deformities while preserved mental development.

Materials and methods: In the present investigation, radiological workup as well as lysosomal enzyme assay and genetic mutation were performed according to the standard protocols.

Results: Here, we report a single affected individual (boy) having Saudi origin, suffering from rare mucopolysaccharidosis, MPS-IVA. The main presenting complaint is the unexplained sever pectus carinatum in early infancy period. dysostosis multiplex found in skeletal survey and lysosomal enzymatic analysis revealed absence of N-acetylgalactosamin-6-s enzyme support the final diagnosis of MPSIVA which confirmed by genetic mutation in GALNS gene .

Conclusion: Patients with unexplained pectus Carinatum and bone deformities as well as dysostosis multiplex changes must be tested for mucopolysaccharidosis. Hence, early treatment with enzyme replacement therapy decreases the morbidity and mortality of the disease. Futher Management requires a multidisciplinary approach involving pediatrician, orthopedics, surgery, psychiatry, and clinical geneticist, Genetic counselling an essential part of prevention measures.