P498: Atypical presentation of Alexander disease in a 4-month-old infant: Emphasizing the importance of integrated genetic and biochemical testing

widely spaced teeth), and therefore a diagnosis of a lysosomal storage disorder was suspected.Our patient also presented with hepatosplenomegaly, umbilical hernia, frequent ear infections and mixed conductive/ sensorineural hearing loss (diagnosed via tympanograms, OAEs, and ABRs).Diagnostic Workup: His initial workup found a low Factor VIII and prolonged PTT.MPS enzyme activity panel revealed low iduronate-2 sulfatase activity (0.83 mol/L/hr; Ref: Normal > 5.21 umol/L/hr).A skeletal survey showed broad joints, and an abdominal US showed hepatosplenomegaly.Both an echocardiogram and brain MRI were initially normal.Gene panel testing revealed two separate pathogenic variants, a frameshift variant in the IDS gene (c.1216_1217del;p.Leu406Phefs*24), associated with X-linked mucopolysaccharidosis II and an intronic variant in the F8 gene (c.5219+3A>G)associated with hemophilia A.