Hunter Syndrome (MPS II)
Patient Information
Characteristics
Background and History
The mucopolysaccharidoses are a group of inherited metabolic disorders that result from a deficiency of enzymes required for the breakdown of intracellular molecules. Charles Hunter, a Canadian internist first described this type in two brothers in the 1950s.
Clinical Correlations
Individuals with this disorder may be diagnosed as early as 2 years of age when children present with an enlarged liver and spleen together with evidence of developmental delays. They are often short in stature with a coarse facies, short neck, barrel chest and a prominent abdomen. The joints may be stiff and the skull is often enlarged. There is a wide range of clinical disease and many patients are only mildly affected with normal intelligence while others have severe breathing and heart problems. Hearing loss and behavior problems are often present.
Genetics
Inheritance
This disorder is caused by a mutation in a gene on the X-chromosome and therefore occurs primarily in males. Rare females who are affected may have loss of DNA from the X-chromosome instead of a simple gene mutation. Females who carry the mutation can expect that half of their sons and none of their daughters will inherit type II mucopolysaccharidosis.
Pedigree
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.
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'.
Diagnosis and Prognosis
This disorder is usually diagnosed by pediatricians early in life although mild cases may not come to attention until later. One form is considered to be associated with more severe disease, more rapid progress and death may occur in adolescence, often from respiratory and cardiac complications. The more mild form does not progress as rapidly and is compatible with life into the seventh decade. Patients with the latter form usually have normal intelligence.
Various forms of treatment are under investigation, including bone marrow transplantation and enzyme replacement therapy. Early indications suggest these treatments may be helpful but more study is necessary.
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