WHAT IS HUNTER SYNDROME (MPS II)?

The mucopolysaccharidoses (MPS) are a group of lysosomal storage disorders caused by deficiency of enzymes that catalyze the degradation of glycosaminoglycans (GAGs).¹ The MPS disorders are rare diseases and share many clinical features.¹ The specific enzyme deficiency present categorizes the MPS disorders into distinct types.¹ All types are inherited in an autosomal recessive manner, except MPS II, which is also called Hunter syndrome.¹

Hunter syndrome is a rare, X-linked, recessive disorder that almost exclusively affects males.¹ The estimated prevalence of Hunter syndrome is 1 in 162,000 male live births.² Hunter syndrome is characterized by a deficiency in the activity of the lysosomal enzyme iduronate-2-sulfatase (I2S), which is one of the lysosomal enzymes responsible for degrading GAGs.³ Undegraded or partially undegraded GAGs progressively accumulate within tissues and organs, causing the multisystemic signs and symptoms of Hunter syndrome.^1,4

Hunter syndrome has traditionally been categorized into two forms based on neurological involvement; however, the condition is better regarded as a continuum between the two types: neuropathic and non-neuropathic (previously known as severe and attenuated, respectively).^5,6 Two-thirds of patients present with central nervous system involvement, representing the more severe end of the phenotypic spectrum.³