Severe Hunter syndrome (mucopolysaccharidosis II) phenotype secondary to large deletion in the X chromosome encompassing IDS, FMR1, and AFF2 (FMR2).

A 2-year-old boy with an initial diagnosis of Hunter syndrome (mucopolysaccharidosis II) had a more severe phenotype than expected, which warranted further evaluation. The patient had severe infantile global neurodevelopmental delays, macrocephaly with a prominent forehead, coarse facial features with clear corneas, chronic congestion with snoring, wide-spaced teeth, short thick neck, hepatomegaly, an inguinal hernia repaired, early clawhand deformities, and severe generalized hypotonia. X chromosome microarray revealed a large deletion encompassing the genes IDS, FMR1, and AFF2 (FMR2) confirming the diagnoses of both Hunter and fragile X syndromes. This case is also a reminder to clinicians that for optimum patient care, further diagnostic testing is warranted if there is concern that a patient's phenotype is more severe or complex than would be expected for the initial neurogenetic diagnosis.