Correlation of MR imaging and MR spectroscopy findings with cognitive impairment in mucopolysaccharidosis II

Localized donor cells in brain of a Hunter disease patient after cord blood stem cell transplantation

The efficacy of hematopoietic stem cell transplantation (HSCT) for Hunter disease (deficiency of iduronate-2-sulfatase, IDS) remains unclear. We treated a 6-year-old male suffering from a severe type of Hunter disease with cord blood stem cell transplantation (CBSCT); however, he died at 10 months post-therapy due to a laryngeal post-transplantation lymphoproliferative disorder. During the follow-up period after CBSCT, his hyperactivity, estimated mental age, and brain MR findings had not improved. We assessed the efficacy of CBSCT by biochemical and pathological analyses of the autopsied tissues. There were many distended cells with accumulated substrate in the brain, but not in the liver. IDS enzyme activity in the cerebrum remained very low, although that in the liver reached about 40% of the normal control level. However, a variable number of tandem repeats analyses demonstrated a weak donor-derived band not only in the liver but also in the cerebrum. Furthermore, IDS-immunoreactivity in the liver was recognized broadly not only in Kupffer cells but also in hepatocytes. On the other hand, IDS-immunoreactivity was recognized exclusively in CD68-positive microglia/monocytes in the patient's brain; whereas that in the normal brain was also detected in neurons and oligodendrocytes. These donor-derived IDS-positive cells were predominantly localized in perivascular spaces and some of them were evidently present in the brain parenchyma. The efficacy of CBSCT was judged to be insufficient for the brain at 10 months post-therapy. However, the pathological detection of donor-derived cells in the brain parenchyma suggests the potential of HSCT for treatment of neurological symptoms in Hunter disease. This is the first neuropathological report documenting the distribution of donor-derived cells in the brain after CBSCT into a Hunter disease patient.

Neurological findings in Hunter disease: pathology and possible therapeutic effects reviewed

Hunter disease (mucopolysaccharidosis type II, MPS II) is an X-linked lysosomal storage disease caused by deficiency of iduronate-2-sulfatase. Accumulation of chondroitin sulfate B and heparan sulfate in various tissues is the biochemical consequence of MPS II. Children with Hunter disease are normal at birth, and symptoms occur between 2 and 10 years of age. Typical symptoms include coarse facies with enlarged tongue and prominent forehead as well as a short, stocky built stature with short neck. The cardiovascular, respiratory and gastrointestinal systems may be affected, and oral, dermatological and psychiatric as well as neurological complications are described. Life expectancy is markedly reduced and may be limited to 12 years for severely affected patients. The most common causes of death are airway obstruction and cardiac failure. The most severe symptoms may result from neurological symptoms or complications including hydrocephalus, spinal cord compression, cervical myelopathy, optic nerve compression, and hearing impairment. Patients may also develop carpal tunnel syndrome, sleep apnoea, seizures or mental retardation. This review describes characteristic neurological manifestations in MPS II and its underlying pathophysiology. In addition, an appraisal is given whether or not enzyme replacement therapy may be able to improve in particular the neurological symptoms of Hunter disease.

Magnetic resonance imaging findings in Hunter syndrome

Hunter syndrome is a rare genetic lysosomal storage disease that is caused by a deficiency, or absence, of iduronate-2-sulphatase, an enzyme needed to break down specific glycosaminoglycans (GAGs). As a result, GAGs build up in various tissues throughout the body leading to adverse neurological and non-neurological effects. This literature review focuses on the neurological findings. Although few magnetic resonance imaging studies have been conducted, those done have shown that patients with Hunter syndrome generally exhibit brain atrophy, enlarged periventricular spaces and ventriculomegaly. Similar findings have been reported in other mucopolysaccharide disorders. Enzyme replacement therapy is a novel treatment which has had success in treating peripheral disease in mice and humans.

CONCLUSION

Future studies should focus on how structural and chemical signatures in the brain of Hunter patients are altered before and after enzyme replacement therapy, and how those alterations correlate with clinical outcome.