OMIM ID:
Hunter Syndrome (MPS II)
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Corneal clouding may be noted as early as 6 months of age but is usually absent. When present it is milder than in some other forms of mucopolysaccharidosis. A pigmentary retinopathy with variable severity is often present. The disc may be elevated and appears swollen. Secondary optic atrophy may be seen in long standing cases.
Systemic Features
Mild to severe developmental delays are common and mental retardation has been reported in some cases. There is often ‘pebbling’ of the skin over the neck and chest. Joint stiffness, short stature, and skeletal deformities are common. Many have short necks, a protuberant abdomen, a broad chest, and facial coarseness. Hepatosplenomegaly, hearing loss, hernias, and carpal tunnel syndrome are often present. The skull is large with a J-shaped sella, the vertebral bodies are hypoplastic anteriorly, the pelvis and femoral heads are hypoplastic and the diaphyses are expanded.
A severe form, type A, has its onset in the first two to four years of life, with more rapid progression and death commonly by adolescence. Many patients have obstructive pulmonary disease and heart failure. The IDS deficiency is similar to that of type B which is less severe and compatible with life into the 7th decade. Intelligence is often normal in type B.
Genetics
Inheritance
Hunter syndrome, or MPS II, is one of seven lysosomal enzyme deficiencies responsible for the degradation of mucopolysaccharides, and the only one known to be X-linked (Xq28). The mutation in IDS leads to a deficiency of iduronate sulfatase resulting in accumulation of dermatan and heparin sulfate. Rare affected females may have chromosomal deletions instead of a simple mutation in IDS.
Pedigree
X-linked recessive, carrier mother
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
X-linked recessive, father affected
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.