Hurler Syndrome (HS) is a lysosomal storage, X-linked autosomal recessive disorder of the aminomucopolysaccharide Type IH (MPS-IH). It is caused by the excessive build-up of glycosaminoglycans (GAG) in lysosomes. It is caused by mutations on chromosome 4 (4,p16.3) with deficiency in alpha-L-iduronidase enzyme leading to lysosomal degradation. It causes organ systems damage in CNS, skeletal, corneal, and heart. Abnormal changes appear by 3 months of age with progressive developmental and mental deterioration. There's a large head, frontal bossing, and short stature. By age 4 years, there's a developmental arrest. Diagnosis: amniocentesis, and genetic testing. Hurler syndrome is characterized by neutrophil hypersegmentation and the presence of Alder-Reilly inclusions on histopathology. The accumulation of glycosaminoglycans, protein-carbohydrate complexes within lysosomes, form the specific and pathognomic Alder-Reilly inclusions of Hurler Syndrome. Ddx. Other types of mucopolysaccharidosis types like Hurler-Schei and Schei syndromes, which are milder forms. Tx. Enzyme replacement therapy with iduronidase, corneal surgery, surgical bone corrections, and hematopoietic stem cell transplantation (HSCT).