A thoroughly researched, detailed, up to date review of the current and potential future therapeutic options for MPS III. Well worth reading.
Accessing the CNS in MPS disorders remains elusive. Despite recent advances, significant challenges remain. However, some progress is being made.
This article provides a comprehensive review of recent advances, describing the challenges and how they might be overcome. Particular attention is paid to gene editing and base editing, and importantly how these therapies can be delivered to the CNS.
For a more detailed review of recent advances in gene editing, here is a good recent review.
An interesting recent review article on this subject, highlighting the importance of defining a biosimilar. Worth reading.
A team from Stockholm (the Research & Translational Science Unit, Swedish Orphan Biovitrum AB) have recently published the results of a new approach to the treatment of MPS IIIA.
When recombinant enzyme is given intravenously, it is cleared very quickly by cells through their M6P receptors. So little or no enzyme is available for uptake by the brain. The Stockholm team modified the enzyme in such a way that its uptake by M6P receptors was blocked. So the enzyme remained in the circulation for much longer. The results were striking, with significant reduction in levels of heparan sulfate, lysosomal pathology, and inflammation. Importantly, clinical improvement was also seen in several areas.
This approach has been tried before, with limited success. However, the Stockholm team have introduced some important modifications, and their results are certainly superior.
While acknowledging that more work needs to be done, the results have been sufficiently encouraging; the company have now commenced clinical trials. The links are
Here is a link to the published paper
The neurological features of neuronopathic Gaucher disease (nGD), like other LSD’s that affect the CNS, do not respond to ERT. In this paper, Peng et al treated a mouse model with intravenous infusions of iPSC- derived neural stem cells. The preparation used is able to cross the blood brain barrier. There were several beneficial effects of the treatment. Importantly, the levels of acid beta-glucosidase in the brain were higher post treatment and there was some neurological improvement. The authors point out that further work is needed before clinical trials are possible. There are also important challenges of iPSC therapy that need to be overcome. However, an important consideration is that, since no viruses were used, so this approach does not have the disadvantages of gene therapy using viral vectors.
Here is the paper
Enzyme replacement therapy (ERT) for MPS II was licensed in the UK in 2007. Broomfield et al have just published a ten year follow up. This is the first significant review since the Hunter Outcome Survey (HOS) Registry data review in 2017, and adds some important findings:-
1. Cessation of ERT did not trigger a rapid decline (as was reported in the HOS study).
2. Certain features such as cardiac manifestations showed minimal response to ERT.
3. Perhaps most importantly, the neurological features showed a far wider spectrum than previously described. The previously accepted division into “severe” and “attenuated” groups seems to be no longer tenable.
Clearly this last point needs further investigation. The neurological features in MPS II need careful description and delineation, so that clinicians and families are better informed about outcome, and future trials of new treatments can be better designed.
Here is the full paper.
Messenger RNA (mRNA) is a group of molecules that convey genetic information from DNA in the nucleus into the cytosol of the cell. There, this information is used by ribosomes to make protein. So mRNA’s that make specific proteins can be constructed and inserted into a cell, which has the machinery to make the specific protein. This forms the basis of mRNA therapy.
Not surprisingly, the concept is not new, but early attempts were unsuccessful for several reasons. These are now gradually being overcome, and mRNA therapy has become one of the most exciting new therapeutic developments seen for many years, with a wide range of applications. For example, it can be used to make vaccines far more quickly and effectively. The possibility of anti-cancer vaccines is also being explored.
Importantly, mRNA therapy provides solutions to some of the drawbacks of gene therapy.
Here is a useful review of mRNA therapy.
Monogenic disorders, such as LSD’s, are prime candidates for mRNA therapy. There has been very encouraging progress in this area. Earlier this year, researchers from Translate Bio, Shire Pharmaceuticals and Biomere successfully treated a mouse model of Fabry disease using mRNA therapy, using the liver as the source of enzyme. Here is their paper
It is probably only a matter of time before mRNA therapy is used to treat more LSD’s. For the time being, however, it is unclear whether it can be sued to treat LSD’s that affect the CNS. We shall have to wait and see.
Cervical spine instability is a well-known complication of mucopolysaccharidosis IVA (Morquio A disease). If left untreated it nearly always results in spinal cord compression and progressive neurological deterioration. Timely surgery can be not only life-saving but may prevent irreversible damage to the cervical cord.
MRI scan of the cervical spine can detect early cord compression, allowing surgeons to intervene early. It has become an essential part of monitoring MPS IVA.
In a recent paper, Broomfield and colleagues at the Royal Manchester Children’s Hospital have described their experience of cervical spine surgery in MPS IVA over an eighteen-year period. Their findings of course confirm previously reported experience as above. However, they also include six patients who developed clinical signs of cord compression in the absence of any MRI changes. This is an important observation and a timely message. It underlines the importance of careful clinical examination, as well as the danger of over-reliance on MRI scans.
Here is the full reference with the link to the paper (pdf kindly supplied by Dr Broomfield).
There have been a number of interesting publications over the last year on MPS II.
Whiteman and Kimura (Shire Inc.) have written a comprehensive overview of the development of idursulfase therapy. Here is the full article
Muenzer et al reported the results of follow up of patients receiving ERT. Data from the Hunter Outcome Survey (HOS) was used for this purpose. A total of 639 patients (excluding females, those patients who had received HSCT, and patients enrolled in the phase 1/2 [TKT018] or phase 2/3 [TKT024] clinical trials) who had been followed up for at least 6 months on ERT were reported. Continuing improvements were observed in various visceral parameters. However, results of cognitive function were not reported. The authors acknowledge some shortcomings of this study. For example, collection of urine for GAG analysis is more difficult in patients with severe neurological involvement.
Here is the full paper
Burton et al report survival in MPS II patients. Again, their data is drawn from HOS. Two key findings are
- A 54% increase in survival in treated vs untreated patients
- A five fold higher risk of death in patients with cognitive impairment.
Here is the full paper
These findings are not surprising, but they emphasise the need for early diagnosis of, and more effective treatments for, the brain involvement in MPS II.
Escolar et al reported a scoring system for early diagnosis of CNS disease. They found that seven early clinical markers and a severity score index of CNS involvement can be used for initial screening of children who might benefit from CNS-directed therapies. This paper has not received the attention that it should have; the severity score described should be more widely used.
Here is the full paper
As far as treatment of brain involvement in MPS is concerned, Scarpa et al have written this timely review of recent developments in the field.
Here is their full paper
Mucopolysaccharidosis type II is often associated with challenging, disruptive behaviour and varying rates of cognitive decline. However, the underlying mechanisms are only poorly understood.
Now, several teams from Padova, Italy, have published findings that shed new light on this area. They performed an analysis of the MPS II mouse brain, using RNA sequencing (RNA-Seq). A detailed description is beyond the scope of this post, but basically RNA-Seq is an example of next generation sequencing that is widely used to study gene expression by transcriptome profiling. The transcriptome is the complete set of transcripts in a cell, and their quantity, for a specific developmental stage or physiological condition. Understanding the transcriptome is essential for interpreting the functional elements of the genome and revealing the molecular constituents of cells and tissues, and also for understanding development and disease.
The researchers investigated genes known to be involved in many aspects of neurological function. They found that there was dysregulation of many of these genes, for example calcium homeostasis, axon guidance, mitochondrial function, oxidative stress and circadian rhythm.
Several of these, for example mitochondrial function and oxidative stress, are involved in different stages of the Parkinson Disease pathway. A particularly important finding was the upregulation of alpha-synuclein, the accumulation of which is responsible for synucleopathies such as Parkinson’s disease (PD). For many years, Gaucher disease was the only lysosomal storage disorder (LSD) thought to be associated with PD. However, in recent years such as association has been described in other LSD’s such as Niemann-Pick disease type I and sphingomyelinase deficiency. Accumulation of alpha-synuclein has been demonstrated in the cortex of patients with MPS III. While PD has not yet been described in MPS II patients, it seems that it is only a matter of time before such an association is reported.
Alpha-synuclein also contributes to the development of Alzheimer’s disease. Its accumulation may therefore be of relevance to the cognitive decline that is seen in many MPS II patients.
It is quite possible that patients with MPS II will be found to have similar patterns of gene dysregulation to those seen in the mouse model. Were this to be found to be the case, it may well have implications for counselling and management.
However, a note of caution is required. The MPS II mouse has a single mutation; whereas human MPS II is caused by many mutations in the IDS gene. So even assuming that similar gene dysregulation to that seen in the mouse will be seen in human MPS II, we dont know how this will be linked to the individual mutations seen in patients. For example, will the gene controlling circadian rhythm be affected more severely in patients with certain MPS II mutations than others?
We also need to bear in mind that, while some aspects of human behaviour may be controlled by the genome, others may well be related to as yet unidentified epigenetic factors. Epigenetics is the term given to the modification of gene expression rather than the genetic code itself. The human epigenome has not yet been fully characterised; work on this is under way.
It may therefore be some time before we have answers to these important questions. Nevertheless, these are important findings that are likely to greatly improve our understanding of the complex neurological and neuropsychiatric features seen in MPS II.