Mucopolysaccharidosis type IIIC (Sanfilippo): early clinical presentation in a large Turkish pedigree

The natural history of neurocognition in MPS disorders: A review

MPS disorders are associated with a wide spectrum of neurocognitive effects, from mild problems with attention and executive functions to progressive and degenerative neuronopathic disease. Studies of the natural history of neurocognition are necessary to determine the profile of abnormality and the rates of change, which are crucial to select endpoints for clinical trials of brain treatments and to make clinical recommendations for interventions to improve patients' quality of life. The goal of this paper is to review neurocognitive natural history studies to determine the current state of knowledge and assist in directing future research in all MPS disorders. There are seven different types of MPS diseases, each resulting from a specific enzyme deficiency and each having a separate natural history. MPS IX, will not be discussed as there are only 4 cases reported in the literature without cognitive abnormality. For MPS IH, hematopoietic cell transplant (HCT) is standard of care and many studies have documented the relationship between age at treatment and neurocognitive outcome, and to a lesser extent, neurocognitive status at baseline. However, the mortality and morbidity associated with the transplant process and residual long-term problems after transplant, have led to renewed efforts to find better treatments. Rather than natural history, new trials will likely need to use the developmental trajectories of the patients with HCT as a comparators. The literature has extensive data regarding developmental trajectories post-HCT. For attenuated MPS I, significant neurocognitive deficits have been documented, but more longitudinal data are needed in order to support a treatment directed at their attention and executive function abnormalities. The neuronopathic form of MPS II has been a challenge due to the variability of the trajectory of the disease with differences in timing of slowing of development and decline. Finding predictors of the course of the disease has only been partially successful, using mutation type and family history. Because of lack of systematic data and clinical trials that precede a thorough understanding of the disease, there is need for a major effort to gather natural history data on the entire spectrum of MPS II. Even in the attenuated disease, attention and executive function abnormalities need documentation. Lengthy detailed longitudinal studies are needed to encompass the wide variability in MPS II. In MPS IIIA, the existence of three good natural history studies allowed a quasi-meta-analysis. In patients with a rapid form of the disease, neurocognitive development slowed up until 42 to 47 months, halted up to about 54 months, then declined rapidly thereafter, with a leveling off at an extremely low age equivalent score below 22 months starting at about chronological age of 6. Those with slower or attenuated forms have been more variable and difficult to characterize. Because of the plethora of studies in IIIA, it has been recommended that data be combined from natural history studies to minimize the burden on parents and patients. Sufficient data exists to understand the natural history of cognition in MPS IIIA. MPS IIIB is quite similar to IIIA, but more attenuated patients in that phenotype have been reported. MPS IIIC and D, because they are so rare, have little documentation of natural history despite the prospects of treatments. MPS IV and VI are the least well documented of the MPS disorders with respect to their neurocognitive natural history. Because, like attenuated MPS I and II, they do not show progression of neurocognitive abnormality and most patients function in the range of normality, their behavioral, attentional, and executive function abnormalities have been ignored to the detriment of their quality of life. A peripheral treatment for MPS VII, extremely rare even among MPS types, has recently been approved with a post-approval monitoring system to provide neurocognitive natural history data in the future. More natural history studies in the MPS forms with milder cognitive deficits (MPS I, II, IV, and VI) are recommended with the goal of improving these patients' quality of life with and without new brain treatments, beyond the benefits of available peripheral enzyme replacement therapy. Recommendations are offered at-a-glance with respect to what areas most urgently need attention to clarify neurocognitive function in all MPS types.

THE LYSOSOMAL STORAGE DISEASE GM2 GANGLIOSIDOSIS IN CAPTIVE BANDED MONGOOSE SIBLINGS ( MUNGOS MUNGO)

  This study reports the occurrence of the lysosomal storage disease GM2 gangliosidosis (Sandhoff disease) in two 11-mo-old captive-bred, male and female mongoose siblings ( Mungos mungo). The clinical signs and the pathological findings reported here were similar to those reported in other mammalian species. Light microscopy revealed an accumulation of stored material in neurons and macrophages accompanied by a significant neuronal degeneration (swelling of neuronal soma, loss of Nissl substance, and neuronal loss) and gliosis. Electron microscopy of brain tissue identified the stored material as membrane-bound multilamellar bodies. An almost complete lack of total hexosaminidase activity in serum suggested a defect in the HEXB gene (Sandhoff disease in humans). High-performance thin-layer chromatography and mass spectrometry confirmed the accumulation of GM2 ganglioside in brain and kidney tissue, and the lectin staining pattern of the brain tissue further corroborated the diagnosis of a Sandhoff-type lysosomal storage disease.

Incidence and natural history of mucopolysaccharidosis type III in France and comparison with United Kingdom and Greece

Sanfilippo syndrome, or mucopolysaccharidosis type III (MPSIII) is a lysosomal storage disease with predominant neurological manifestations in affected children. It is considered heterogeneous with respect to prevalence, clinical presentation, biochemistry (four biochemical forms of the disease referred to as MPSIIIA, B, C, and D are known), and causative mutations. The perspective of therapeutic options emphasizes the need for better knowledge of MPSIII incidence and natural history. We performed parallel retrospective epidemiological studies of patients diagnosed with MSPIII in France (n = 128), UK (n = 126), and Greece (n = 20) from 1990 to 2006. Incidences ranged from 0.68 per 100,000 live-births in France to 1.21 per 100,000 live-births in UK. MPSIIIA, which predominates in France and UK, was absent in Greece, where most patients have MPSIIIB. The study confirmed the large allelic heterogeneity of MPSIIIA and MPSIIIB and detected several yet undescribed mutations. Analysis of clinical manifestations at diagnosis and over a 6-7 years follow-up indicated that almost all patients, whatever the disease subtype, expressed neurological manifestations before the age of 5 years, including language acquisition delay, cognitive delay, and/or abnormal behavior. In contrast to relatively homogeneous early onset manifestations, disease progression showed significant variation depending on subtype and age at diagnosis. Different severities of disease progressions and different allele distribution between France and UK suggested that mutations are not equally deleterious, although genotype-phenotype correlation could not be established. Notwithstanding the rapidity of further clinical deterioration, all MPSIII patients suffer early onset devastating neurological manifestations that deserve early treatment when available.

Clinical and genetic spectrum of Sanfilippo type C (MPS IIIC) disease in The Netherlands

Mucopolysaccharidosis IIIC (MPS IIIC, Sanfilippo C syndrome) is a lysosomal storage disorder caused by deficiency of the lysosomal enzyme acetyl-CoA:alpha-glucosaminide N-acetyltransferase (HGSNAT). We performed a clinical study on 29 Dutch MPS IIIC patients and determined causative mutations in the recently identified HGSNAT gene. Psychomotor development was reported to be normal in all patients during the first year of life. First clinical signs were usually noted between 1 and 6 years (mean 3.5 years), and consisted of delayed psychomotor development and behavioral problems. Other symptoms included sleeping and hearing problems, recurrent infections, diarrhoea and epilepsy. Two sisters had attenuated disease and did not have symptoms until the third decade. Mean age of death was 34 years (range 25-48). Molecular analysis revealed mutations in both alleles for all patients except one. Altogether 14 different mutations were found: two splice site mutations, one frame shift mutation due to an insertion, three nonsense mutations and eight missense mutations. Two mutations, p.R344C and p.S518F, were frequent among probands of Dutch origin representing 22.0% and 29.3%, respectively, of the mutant alleles. This study demonstrates that MPS IIIC has a milder course than previously reported and that both severity and clinical course are highly variable even between sibs, complicating prediction of the clinical phenotype for individual patients. A clear phenotype-genotype correlation could not be established, except that the mutations p.G262R and p.S539C were only found in two sisters with late-onset disease and presumably convey a mild phenotype.

Scoring evaluation of the natural course of mucopolysaccharidosis type IIIA (Sanfilippo syndrome type A)

OBJECTIVE

Mucopolysaccharidosis types IIIA through IIID (Sanfilippo syndrome) are caused by deficiencies of enzymes involved in the degradation of heparan sulfate. The onset and severity of the disease are highly variable. The purpose of this study was to describe the natural course of mucopolysaccharidosis type IIIA in a large cohort of patients.

PATIENTS AND METHODS

The natural course of mucopolysaccharidosis type IIIA was assessed in 71 patients by using a detailed questionnaire and a 4-point scoring system and compared with the course of the disease in 14 patients with mucopolysaccharidosis type IIIB and 4 patients with mucopolysaccharidosis type IIIC.

RESULTS

In the cohort of patients with mucopolysaccharidosis type IIIA, first symptoms of disease were observed, on average, at 7 months of age. Speech and motor development were delayed in 66.2% and 33.9% of patients, respectively. The median age at diagnosis was 4.5 years. The onset of regression in speech, motor, and cognitive function was observed at an average age of 3.3 years. The loss of all 3 of the assessed abilities was observed at an average age of 12.5 years. Speech was lost before motor and cognitive functions. In a small group of patients who were >12.5 years of age (9.9%), speech, motor, and cognitive skills were partially preserved up to a maximum age of 23.8 years.

CONCLUSIONS

To our knowledge, this is the first systematic and comprehensive study on the natural course of mucopolysaccharidosis type IIIA. The 4-point scoring system may be used to classify patients into groups with a rapid or slower course of the disease. This may have an important impact on parental counseling as well as therapeutic interventions.