Huntington cleavage induced by Thrombin in vitro.
Normal huntingtin function: an alternative approach to Huntington's disease.
Young people's experiences of growing up in a family affected by Huntington's disease.
The complexity of reproductive decision-making in asymptomatic carriers of the Huntington mutation.
Pharmaceutical, cellular and genetic therapies for Huntington's disease.
Botox reduces excessive drooling in neurologically impaired children.
Counting CAG repeats in the Huntington's disease gene by restriction endonuclease EcoP15I cleavage.
Molecular analysis of the (CAG)n repeat causing Huntington's disease in 34 Iranian families.
Cognitive Correlates of Obsessive and Compulsive Symptoms in Huntington's Disease. (1)
Cognitive Correlates of Obsessive and Compulsive Symptoms in Huntington's Disease. (2)
Attachment in families with Huntington's Disease. A paradigm in clinical genetics.
Lin, F., Wu, J., Wang, Y. and Qin, Z. Huntington cleavage induced by Thrombin in vitro. Acta Biochimica et Biophysica Sinica(2007), 39(1): 15-18.
HD is caused by an expansion of a trinucleotide (CAG) repeat encoding glutamine in the N-terminal of Htt. Several proteases cleave Htt within the N-terminal region. Sequence analysis of Htt revealed a possible thrombin cleavage site in the N-terminal region of the Htt.
Thrombin is a multifunctional protease known for its role in the blood coagulation cascade. It was thought to be present in the liver, but by using sensitive detection method, researchers were able to show its presence in the brain during development. Not only thrombin but also pro-thrombin was shown to be present in the brain. These studies suggest that thrombin may have other roles as yet undiscovered.
This paper reported a study that showed thrombin cleaved wild-type Htt in vitro. Therefore, there is a need to investigate if thrombin would cleave Htt in vivo and its significance in the pathophysiology of HD.
(Annotation by Angela Hamilton)
Kaptein, A.A., Scharloo, E.M., Helder, E., Snoei, L., van Kempen, G.M.J., Weinman, E., van Hourwelingen, J.C., Roos, R.A.C. Quality of life in couples living with Huntington's Disease: the role of patients' and partners' illness perceptions Qual Life Res.(2007);16: 793-801.
This paper was examining whether patients of HD perceive their illness differently to their partners, in the context of quality of life. Kaptein and colleagues were investigating if differences in the perception of disease between patients and their partners can have negative impact on quality of life. The patients investigated were early to middle stage HD. Quality of life research refers both to the social environment of the affected patients, but also the broader effect of the illness on partners and families.
There are five factors which influence a patient's perception of disease: the identity of the disease and its symptoms; the personal ideas patients have about the cause of the disease; the duration of the illness; the expected outcomes; and the controllability or curability of the illness. Studies have shown that the illness perception of spouses can also affect a patient's perception of disease, including their coping mechanisms and overall well being, both of which have significant effect on quality of life.
For many of the factors affecting illness perception, the study identified that patients and their partners held similar views, particularly regarding causes, outcomes, and curability. However, the study identified significant differences in the perception of disease identity between patients and their partners. In particular, partners reported more symptoms of HD than the patients did. Furthermore, the patients held more positive views with regards to the controllability of the disease than their partners. Spousal perceptions were not found to significantly affect patient quality of life; however they had a large effect on patient vitality.
(Annotation by Alana Shepherd)
L. Ciu, H. Jeong, F. Borovecki, C. N. Parkhurst, N. Tanese and D. Krainc. Transcriptional Repression of PGC-1α by Mutant Huntington leads to Mitochondrial Dysfunction and Neurodegeneration. Cell 2006; 127: 59-69.
In the last few years, transcriptional deregulation and altered energy metabolism have been implicated in the development of Huntington's disease (HD). This study identifies a key role for transcriptional co-activator PGC-1α in the control of energy metabolism in the early stages of HD pathogenesis. Researchers show that in normal state, PGC-1α maintains energy homeostasis in the central nervous system but in HD, PGC-1α expression is disrupted by the mutant huntingtin protein. The results report:
1) Decreased expression of PGC-1α in striatum of HD brain
2) Mutant huntingtin inhibits transcription of PGC-1α
3) PGC-1α protects against mutant huntingtin-induced mitochondrial dysfunction and striatal toxicity
The researchers hypothesize that in HD, mutant huntingtin interferes with CREB/TAF4 regulation of PGC-1α transcription leading to inhibited expression of PGC-1α. This inhibition limits the ability of vulnerable neurons to adequately respond to energy demands resulting in toxic effects on energy-dependent neuronal pathways.
(Annotation by Zehra Elgundi)
S. L. Crick, M. Jayaraman, C. Frieden, R. Wetzel and R. V. Pappu. Fluorescence correlation spectroscopy shows that monomeric polyglutamine molecules form collapsed structures in aqueous solutions. Proceedings of the National Academy of Sciences (2006); 103: 16764-16769. Available from Proceedings of the National Academy of Sciences.
Different hypotheses have been put forth to explain the toxicity associated with the genetic expansion of polyglutamine as seen in a number of neurodegenerative diseases including Huntington's disease. The majority of proposed mechanisms centre on the aggressive, length-dependent, ability of polyglutamine to form ordered intermolecular aggregates.
In this study, the researchers use a technique called fluorescence correlation spectroscopy to quantify the hydrodynamic sizes of monomeric polyglutamine by quantifying chain size as a function of chain length. They report that in aqueous environments such as water, polyglutamine molecules behave like chains in poor solvent where chain-chain interactions are favoured resulting in collapsed, roughly spherical structures and as concentrations increase they form intermolecular aggregates.
(Annotation by Zehra Elgundi)
Cattaneo, E., Zuccato, C. & Tartari, M. Normal huntingtin function: an alternative approach to Huntington's disease. Nature Reviews (2005); 6: 919-930.
Huntington Disease is caused by a mutation of the protein huntingtin which is signified by an expansion of part of the protein (polyQ region) responsible for the loss of a subset of neurons culminating in the pathogenesis of the disease.
Many other regions of the protein had been identified with specific functions of the huntingtin, not necessarily connected with the disease itself. There are other sectional repeats, conformational and cleavage sites that may be involved in protein-protein interactions. Most of these experiments were done on fruitflies (D. melanogaster) and mice. Fruitflies' huntingtin doesn't seem to have polyQ section, whilst polyQ regions appeared in fishes and continued to exist in vertebrates during evolution, becoming polymorphic only in humans.
Recently it has been suggested that since huntingtin itself must have some normal function in the general cellular activity (it is essential in embryogenesis and it universally exists in and outside the nervous system), perhaps the loss of huntingtin and/or its reduced activity may prove pathological to the organism.
During embryogenesis, huntingtin is essential to gastrulation (approx. day 8) and the development of nervous system. During development, mutant huntingtin has the same activity as the wild-type (naturally occurring) protein; in adulthood, wild-type huntingtin controls the activity of mammalian neurons.
Therefore, is the loss of wild-type huntingtin involved in the disease process? The authors reviewed an extensive list of studies; firstly, they discussed the structure and evolution of huntingtin in order to understand its functions. Then, by comparing the various functions of the wild-type and the mutant huntingtins, they tried to tease out the answer to the question. From this review, there seems to be evidence that reducing the level of wild-type huntingtin or increasing the expression of mutant huntingtin reach the same conclusion which suggest that some of the molecular dysfunctions observed in HD are due to the decreased level of wild-type huntingtin. Needless to say that more work need to be done, both to continue to unravel the mechanism of the neuronal development and to find the therapeutic implication toward treatment of HD.
(Annotation by Angela Hamilton)
Forrest Keenan, K., Miedzybrodzka, Z., van Teijlingen, E., McKee, L. and Simpson, S.A. Young people's experiences of growing up in a family affected by Huntington's disease. Clinical Genetics. (2007):71:120-129
Huntington's Disease (HD) affects families of the sufferers. Because the average age of onset is between 30 to 45 years it unavoidably has an impact on the young people (YP) who grow up within the nuclear family or in the extended family. This paper explores the experiences of YP in dealing with the risk of contracting the disease, as well as carrying the burden of caring and parenting the afflicted parent. Even those who haven't had to play the caring role are affected in their development and stages of evolving maturity. Adolescence is a critical time in a child's development and living with a parent with H D may have a negative impact.
A child may live in a constant state of anxiety, too self-conscious to reveal HD to his peers thereby damaging the establishment of peer relations and transition to independence as well as the initiation of intimate relationship. However, this study aims to highlight the resilience displayed by YP in HD affected families.
On the whole, the results reveal four main themes: YP as carers, the worried well, those who cope and those at risk/in need. These are by no means exclusive enclaves, for their experiences can fall into more than one theme, and this will vary over time.
YP as carers. These are YP under 18 who assume a level of responsibility for an affected parent or sibling, carrying out caring tasks normally undertaken by adults. Of particular concern is the YP who had become young adult carer (over 18 YP) who would find it difficult to be financially independent of their parents.
Those who cope. This study found that participants who cope well used a mixture of emotion-focused (avoidance, assimilation, seeking social support etc.) and problem solving focused strategy (seeking information, changing lifestyle, planning for the future).
The worried well. This group of people are affected by psychosocial problems like excessive tiredness, lack of self-esteem, avoidance of relationship, excessive symptoms searching, severe anxiety, panic attacks, insomnia etc. Invariably they found out about HD in their late teens or early twenties, and it came as a shock to them.
Those at risk/in need. This is the group which has the compounded problems from their caring activities, their own anxiety of being at risk of the disease, abuse from the HD affected parent and unmet need for professional and family support.
This study confirms previous research outcome that the experience of YP in an HD affected families can be quite varied, any professional support may need to be tailored to almost individual needs. A policy of 'reaching out', where contact is actively made, may be the best way to offer assistance and support.
(Annotation by Angela Hamilton)
Decruyenaere, M., Evers-Kiebooms, G., Boogaerts, A., Philippe, K., Demyttenaere, K., Dom, R., Vandenberghe, W., Fryns, J.P. The complexity of reproductive decision-making in asymptomatic carriers of the Huntington mutation. European Journal of Human Genetics. (2007); 1018(481).
This study examined the influence of predictive genetic testing for the HD mutation on the decisions made by couples with regards to reproduction. It was based on earlier studies suggesting that family planning was a primary motive for undergoing a predictive test.
There are two main types of predictive test: prenatal diagnosis (PD) and pre-implantation diagnosis (PGD). HD-positive PD results (that is, the embryo tests positive for the mutated HD gene) can lead to pregnancy termination; alternatively PGD is carried out during IVF, so only embryos without the HD mutation are implanted. Non-disclosure PGD can be carried out such that the carrier-status of the embryo is determined without revealing the carrier-status of the parents; however this presents considerable ethical issues and is not widely accepted.
The study was interview based, and the responses highlighted both benefits and disadvantages for the use of predictive testing. Frequently mentioned benefits of PD were the peace of mind knowing offspring would be unaffected, as well as the comfort and support brought by the child to both the healthy and ill parents.
Key reasons for not utilising PD were an unwillingness to terminate a pregnancy, particularly for a late onset disease; as well as optimism towards future treatments and cures. For many people, the desire to conceive outweighed the potential risk. Several couples mentioned a reluctance to become emotionally attached to the pregnancy until results were known, as well as keeping the pregnancy and/or termination a secret to avoid judgement from third parties.
(Annotation by Alana Shepherd)
Pardo, R., Colin, E., Regulier, E., Aebischer, P., Deglon, N., Humbert, S. and Saudou, F.
Inhibition of Calcineurin by FK506 protects against Polyglutamine-Huntingtin toxicity through an increase of Huntingtin phosphorylation at S421.J. Neurosci. (2006); 26(5): 1635-1645.
Calcineurin (CaN) is a phosphatase which means it is a molecule that helps in the removal of phosphate from other molecules. CaN is present in all tissue in mammals, with notably high levels in the brain. CaN is inhibited by drugs such as cyclosporin A and FK506. In HD, CaN inhibits the action of other enzymes (kinases) that phosphorylate (adding phosphates to) Huntingtin (htt) at the position S421, forming polyQ-htt complex thereby increasing htt's toxicity. Blocking CaN, therefore, should increase phosphorylation and preventing the formation of the polyQ-htt complex.
In previous studies this team of scientists had shown that CaN is the phosphatase that targets htt at S421, in vitro. In this study they aimed to determine whether administration of FK506 could block the activity of CaN and induce the phosphorylation of htt in vivo. FK506, unlike cyclosporin, can readily cross the blood-brain barrier. They used mouse model of HD.
Results: This study extends their previous findings ie. Inducing the phosphorylation of htt at S421 in vivo might have an impact in slowing the progression of HD. They found that blocking the action of CaN with FK506 is a better proposition than increasing htt phosphorylation by increasing the activity of the kinases (enzymes) that promote it. FK506 is routinely used in grafting procedures therefore its safety and tolerability had been established.
(Annotation by Angela Hamilton)
Pardo, R., Colin, E., Regulier, E., Aebischer, P., Deglon, N., Humbert, S., Saudou, F. Inhibition of Calcineuron by FK506 protects against polyglutamine- Huntingtin toxicity through an increase of Huntingtin phosphorylation at S421. Journal of Neuroscience, 26(5): 1635-1645.
Immunosuppressant drug FK506 has shown potential as a treatment for Huntington's disease (HD). Agglutination of the Huntingtin protein interrupts neuronal communication, causing cellular toxicity. HD-affected cells have decreased levels of an innate protein modification process (phosphorylation) which normally reduces neuronal toxicity, but they also have high levels of another protein, Calcineurin, which naturally reverses the modification effects. The combination of these factors essentially increases the toxicity of the Huntingtin protein.
The study was examining the effect of FK506, a Calcineurin inhibitor, on the extent of protein modification. It was demonstrated that administration of FK506 in mice effectively blocks the action of Calcineurin, thus increasing the rate of protein modification and decreasing neuronal toxicity, and potentially slow disease progression.
FK506 has potential to be developed as a treatment for HD. Results were demonstrated in cellular models and in mice. As FK506 is currently a clinically used immunosuppressant, previous therapeutic trials have shown it is safe for human use; further investigation is required to establish whether equivalent neuro-protective effects are observed in human trials.
(Annotation by Alana Shepherd)
O. J. Handley, J. J. Naji, S. B. Dunnett and A. E. Rosser. Pharmaceutical, cellular and genetic therapies for Huntington's disease. Clinical Science (2006) 110:73-88
This is a great review which discusses the current status of treatment and the progress being made towards effective pharmaceutical- cell- and genetic-based therapies for Huntington's disease (HD).
At present, existing pharmaceutical therapies manage the symptoms rather than preventing and delaying disease progression. More recently, significant progress is being made in developing strategies for prevention and repair. Some examples are summarized below:
| Target Mechanism | Drug | Clinical Trial Results |
| Caspase inhibitor - inhibits the enzymes responsible for the initiation of cell death | Minocycline | Drug safety and tolerability recently reported |
| Glutamine receptor blocker - prevents the release of excessive glutamate which plays a part in cell death | Lamotrigine | No effect on slowing disease progression however symptomatic improvement reported |
| Novel compound that inhibits harmful enzymes involved in cell death | LAX-101 (Miraxion) | Clinical improvement seen in patients with low CAG repeat numbers |
| Tgase inhibitor - inhibits the enzyme Tgase thought to be a trigger for protein aggregation | Creatine | Two year trial currently underway |
Reparative strategies being investigated include transplantation repair where primary cells are surgically replaced to restore brain circuitry and function lost through cell death as a consequence of neurodegeneration. Animal studies of transplantation show promise with successfully transplanted fetal tissue restoring motor and cognitive function. Despite the ethical and practical limitations of using human fetal tissue for transplantation, six clinical trials have been initiated. The safety and efficacy data to date support the continuation of trials of implanted tissue as potential therapy.
Alternatively, more readily renewable sources of donor cells are being investigated including stem cells. Somatic stem cells offer the greatest potential for therapy. These stem cells are specific to a tissue or organ so can be used to regenerate tissues in which they normally reside. The possibility of using neural stem cells to replace or repair specific brain regions is currently under investigation.
Since the identification of the mutation responsible for HD, the possibility of protecting neural cells using targeted genetic therapies has been considered. The method of delivery to the central nervous system needs to be carefully explored to ensure safety and efficacy. Vectors (gene carriers) utilizing the viral properties of invading cells and manipulated to carry therapeutic genes, have been employed with some success in animal models. Virally delivered growth factor CNTF in rodent models show protective and reparative effects on skilled motor and cognitive tasks as well as preservation of the neuroanatomy of the striatum.
(Annotation by Zehra Elgundi)
F. Squitieri, L. Frati, A. Ciarmiello, S. Lastoria and O. Quarrell. Juvenile Huntington's disease: Does a dosage-effect pathogenic mechanism differ from the classical adult disease? Mechanisms of Ageing & Development(2006) 127:208-212
This is a literature review which compares the clinical, genetic, biochemical and biophysical aspects between juvenile huntington's disease (JHD) and adult onset huntington's disease (HD).
1) Clinical - there is an overlap of neurological symptoms at onset between adult and JHD however rigidity occurs more typically in JHD and is associated with more widespread brain degeneration and a highly progressive disease course. This is demonstrated by magnetic resonance imaging (MRI) which shows more increased rate of brain deterioration by a reduction in grey matter volume between an adult onset patient and JHD patient with identical disease length in years.
2) Genetic - it is widely reported a negative correlation exists between age of onset and expanded CAG repeats in HD. However, modification studies on possible genes relating to age of onset have shown effects on JHD but not on adult HD. Therefore suggesting that mechanisms other than the triplet repeat expansion must contribute to onset and the presenting HD symptoms.
3) Biochemical and Biophysical - cell lines generated from JHD patients with large expansion repeats show biochemical and biophysical changes not seen in cell lines from low or moderate expansions including:
A dosage effect of the number of repeats seems to play a major role in the loss of function of other proteins thus contributing to age of onset and disease course.
(Annotation by Zehra Elgundi)
Yael Waknine. Botox reduces excessive drooling in neurologically impaired children. Medscape 2005.
The preliminary results of a study by the University of Toronto in Ontario, Canada, were released at the AARS 105th Annual Meeting (May 2005), regarding the use of Botulinum toxin A (Botox A) for the treatment of sialorrhea (excessive drooling) in neurologically impaired children.
Botox is currently used as a sialorrhea treatment in adult Parkinson's patients however the effectiveness in children has not been established. The present study aimed to establish the outcomes of use in children, as well as a safe dosage and effective dosing regime.
Although the findings are still preliminary, they indicate that Botox is an effective means of reducing drooling, gurgling, choking and halitosis in neurologically impaired children, who lack the cognitive ability to reflexively swallow. The study continues, with investigation into doses which produce the most benefit, as well as dosing regimes required to sustain benefit.
(Annotation by Alana Shepherd)
Mönche-Buchner, E., Reich, S., Mücke, M., Reuter, M., Messer, W., Wanker, E., Krüger, D.H. Counting CAG repeats in the Huntington's disease gene by restriction endonuclease EcoP15I cleavage. Nucleic Acids Research (2002) Vol 30(16): e83.
The number of CAG repeats has been used as basis for diagnosis of HD for some time: this is currently performed using the Polymerase Chain Reaction (PCR), which amplifies a DNA sample, labelled with a radioactive isotope, for analysis of the number of repeats based on the size of the sample: the bigger the sample, the more repeats present. The pathological range of repeats is generally over 40 units.
The present study was investigating an alternate method for analysing the number of repeats, using Restriction Endonuclease. This method involves 'digesting' the DNA with an enzyme (EcoP15I) which cuts the DNA into fragments, allowing analysis such that the number of fragments correlates to the number of CAG repeats. This method is beneficial compared to PCR because it does not require radioactive labels, thus removes the issue of isotopic waste. Furthermore, the samples are not affected by the risk of DNA deletions or insertions sometimes occurring in PCR, and each DNA fragment is counted directly, so the size of the DNA is irrelevant (a time consuming requirement of PCR).
The use of endonuclease digestion for determining the number of CAG repeats presents a potential method for the diagnosis of many CAG-repeat disorders, including Huntington's Disease, as well as dentatorubral pallidoluysian atrophy, spinal bulbar muscular atrophy and spinocerebellar ataxia.
(Annotation by Alana Shepherd)
F. Hormozian, M. Houshmand, M. H. Sanati, R. Ghiasvand and M. M. Banoie. Molecular analysis of the (CAG)n repeat causing huntington's disease in 34 Iranian families.Indian Journal of Human Genetics 2004 10(2):53-57.
This study represents the first report of molecular analysis of Huntington's disease (HD) among the Iranian population and in the Middle East. Researchers analyse the distribution of CAG repeats in 71 individuals including 34 clinically diagnosed HD patients and 37 unaffected family members.
In the HD patients, CAG repeats varied from 43 to 83 units and in unaffected family members from 31 to 36 units. In 25 unrelated control individuals, CAG repeats varied from 10 to 34 units. This study also reports a significant correlation between age of onset and length of CAG repeats with a tendency for age at onset to decrease as the CAG length increases.
The researchers conclude that molecular genotyping should be conducted in suspected HD patients and is particularly important in sporadic cases of HD for providing correct diagnosis and facilitating genetic counseling to family members.
(Annotation by Zehra Elgundi)
K. E. Anderson, E. D. Louis, Y. Stern and K. S. Marder. Cognitive Correlates of Obsessive and Compulsive Symptoms in Huntington's Disease Am J Psychiatry 2001 158:799-801
The authors' goal was to examine the frequency and type of obsessive and compulsive symptoms in Huntington's disease.
The Yale-Brown Obsessive Compulsive Scale was used to assess obsessive and compulsive symptoms in 27 patients with Huntington's disease. The neuropsychological test performance of the 14 patients with at least one obsessive symptom and the seven patients with at least one compulsive symptom was compared with the performance of the patients without such symptoms.
(The Yale-Brown scale is a two part measure of obsessive and compulsive symptoms. The first component is a checklist designed to elicit obsessive and compulsive symptoms. The second is a measure of symptom severity. Neuropsychological tests include verbal fluency in word reading and colour naming.)
More than half of the patients with Huntington's disease endorsed obsessive or compulsive symptoms on the Yale-Brown scale. Patients with obsessive or compulsive symptoms showed significantly greater impairment on neuropsychological tests measuring executive function than those without such symptoms.
The conclusion was that basal ganglia pathology in Huntington's disease may contribute to production of obsessive and compulsive symptoms and to executive performance deficits in these patients.
(Annotation by Zehra Elgundi)
Anderson, K. E., Louis, E.D., Stern, Y. and Marder, K.S. Cognitive Correlates of Obsessive and Compulsive Symptoms in Huntington's Disease. Am. J. Psychiatry (2001); 158: 799-801.
Huntington's Disease patients were evaluated with the UHDRS (Unified Huntington's Disease Rating Scale) which assesses four domains : neurological, psychiatric, neuropsychological and functional. The aim is to initially compare those patients with obsessive compulsive disorder (OCD) neuropsychologically to the ones without OCD. Then to assess the relationship between OCD and cognitive and/or motor dysfunction.
It was found that patients with OCD perform more poorly on all neuropsychological tests than those without OCD. There is a hint of results physiologically referring to a functional imaging studies that showed that OCD is linked to caudate and frontal cortex abnormalities. Further studies are needed to link OCD in HD with the neuropathology of OCD.
(Annotation by Angela)
Van der Meer, L., Timman, R., Trysburg, W., Duisterhof, M., Erdman, R., Van Elderen, T. and Tibben, A. Attachment in families with Huntington's Disease. A paradigm in clinical genetics. Patient Education and Counseling (2006)
Attachment theory as theoretical framework to study the manner in which HD affects family dynamics. 3 types of attachment:
Two groups (clinical and non-clinical) were interviewed. The clinical group showed a significantly higher percentage of insecure attachment, compared to the non-clinical population. May be useful in genetic counseling.
(Annotation by Angela)
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