Background and Aims: Hunter syndrome (mucopolysaccharidosis type II) is a rare, progressive, X-linked disorder caused by deficiency of the enzyme iduronate-2-sulphatase. The Hunter Outcome Survey (HOS) is a global survey of patients with Hunter syndrome designed to enhance our understanding of the natural history of the disease and to monitor the safety and efficacy of enzyme replacement therapy.

Patients and Methods: Analysis of the HOS database was carried out to examine the clinical features of patients who were diagnosed with Hunter syndrome. As of January 2008, there were 367 prospective patients (defined as “alive” upon entry) enrolled in HOS.

Results: Among the 367 patients within HOS, the earliest clinical manifestations were hernia (1.8 years), otitis media (1.9 years) and nasal obstruction (2.7 years). Facial features of Hunter syndrome, enlarged liver/spleen and enlarged tonsils/adenoids were observed at median ages of 2.9, 3.3 and 3.4 years, respectively. The median age at diagnosis was 3.5 years (10th–90th percentile, 1.2–6.8 years). The most common clinical symptoms were characteristic facial features (91%), enlarged spleen/liver (84%), joint stiffness (82%), hernia (76%), otitis media (72%), enlarged tongue (70%), enlarged tonsils/adenoids (67%) and nasal obstruction (32%).

Conclusions: At approximately 2 years of age, 50% of children with Hunter syndrome already experience hernias and/or otitis media, although this analysis also reveals that the diagnosis is not made until 3.5 years on average. Increased awareness of these early symptoms may aid diagnosis and allow prompt therapeutic intervention in order to halt or slow the natural progression in patients with Hunter syndrome.