Downs Syndrome - Dementia Downs

Downs Syndrome - Dementia

Downs Syndrome and Dementia

There is a definite relation between downs syndrome and dementia as several research studies have indicated. Dementia typically follows as a co morbid condition among adults with Down's syndrome and has a severely crippling effect on the patient. Though some studies show the neurobiological pathways associated with the onset of dementia in DS patients, we are still a long way from a comprehensive understanding of the mechanisms involved. Further research is required in this direction. Periodic screening and an active and involved approach to care giving is necessary to defer the onset of and to minimize the impairment due to dementia associated with DS. Treatment should be prompt for reversible causes of cognitive decline. A collaborative effort on the part of the physicians representing different neurological specialties, nurses and the care givers is essential for providing quality care for people afflicted with DS and other co morbid conditions.

Introduction

Downs syndrome is the most common chromosomal disorder that has a significant impact on cognitive functioning. Statistics show that in the UK, one in every 1000 babies are born with this condition. [BUPA]the condition is of genetic origin and is caused by an extra chromosome 21, which severely impairs the normal cognitive functions. People with downs syndrome are also host to a variety of coexisting and debilitating conditions such as dementia, obesity etc. Dementia in particular, is found to be an associated condition affecting most of the DS population with an average onset age of 20 to 30 years earlier than among healthy population. Statistics show that at least 50% of people with downs syndrome have dementia by the age of 60. [Alzheimer's Society]Alzheimer's type dementia is most common among downs syndrome patients causing severe loss of memory and cognitive functions. The problem is more severe due to the difficulties in early detection of dementia among down syndrome patients as in most cases the tendency is to attribute the cognitive decline as normal part of downs syndrome. Thus clinical intervention for dementia is rather late in most cases of downs syndrome population. The debilitating nature of this combination of disorders places a huge burden on caregivers. Several researchers have focused on studying Down's syndrome and dementia as comorbid conditions and this has contributed to our improved understanding of these disorders and in effective management of DS patients. A brief review of existing literature on the association between these two comorbid conditions would help us better understand the complications and the latest treatment modalities

Literature Review

Alzheimer's type dementia is more common among people with downs syndrome. Stanton and Coetzee 2004 is one of the most significant literature reviews on the relation between downs syndrome and dementia. The reviewers found that dementia is a common condition in downs syndrome patients but there are considerable difficulties in both diagnosis and in the treatment of dementia as a comorbid condition in downs syndrome. Overall, the study revealed that the onset of dementia is closely related to the existence of cognitive disabilities. This review also highlighted that younger people with learning disabilities in the age group of 30 to 40 had a high prevalence of frontal lobe dementia. [Coetzee 2004] Tyrrell et.al 2001 was a comprehensive Irish study which analyzed downs syndrome and associated clinical characteristics. The researchers studied 285 people with downs syndrome and in the age group of 35 to 74. Dementia was diagnosed in the study group based on the modified DSMIV criteria. The researchers used tests such as Down's syndrome Mental Status Examination (DSMSE), Test for Severe Impairment (TSI) and Daily Living Skills Questionnaire (DLSQ). Results from the study revealed that dementia had an overall prevalence rate of 13.3% and it was more common among older DS patients with an average age of 54.7 years. Also, the presence of epilepsy and myoclonus were high risk factors for dementia among Down's syndrome patients. [Tyrrell et.al, 2001]

Downs syndrome - Brain structure

Pinter et.al 2001 studied the physiological structure of brain in children with downs syndrome. The researchers used MRI to examine the hippocampal and amygdala volumes of downs syndrome children. Compared with similar data for normal people, Down's syndrome children showed no significant changes in amygdala volume but the researchers observed that hippocampal volumes were considerably smaller. Hippocampal volume reduction was also observed among adults with Down's syndrome. These results indicate that the reduction in hippocampal volume is more due to developmental problems rather than neurodegenerative changes. [Pinter et.al, 2001] Another more recent study was by Teipel et.al (2003) where the researchers compared 34 nondemented downs syndrome patients with 31 healthy individuals for their hippocampus and corpus callosum size. This was done using MRI scans and volumetric measures. The findings from the study indicated that downs syndrome patients has comparatively lower hippocampal and corpus callosum volumes than the normal subjects of similar age. Their study also showed an age related decrease in size of the hippocampal and corpus callosum volumes among these patients while there was no such observable change among the normal subjects. These results suggest that allocortical and neocortical neuronal changes maybe symptomatic of the onset of dementia in Down syndrome patients. [Teipel et.al, 2003]

Another study focused on the relationship between aggressive behavior in Down's syndrome patients with and without dementia as a co existent condition. Adam et.al 2005 analyzed the severity and the frequency of challenging behavior among Down syndrome patients. The researchers proceeded by interviewing the caretakers of the patients with DS using the Aberrant Behaviour Checklist-Community version to document the frequency and severity of challenging behavior. The results indicated that patients in the dementia group exhibited more frequent and more violent behavior than those without dementia. This suggests that aggressive behavior maybe symptomatic of the onset of dementia among Downs's syndrome patients. [Adam et.al, 2005]

Genetic factors for Dementia in DS

It has been known that people with Down's syndrome are at high risk for dementia. Some research has focused on the possible genetic causes for the condition and also on other risk factors that influence the age of onset of dementia among DS patients. A 2002 study by Nicole Schupf, PhD tried to examine these cofactors, which affect the age of onset of dementia among DS patients. The researcher looked for factors such as atypical karyotypes, susceptibility genotypes, oestrogen and ass peptide levels, etc. that affect the levels of beta amyloid. It transpired from the results that oestrogen deficiency, apolipoprotein http://bjp.rcpsych.org/math/epsi.gif

4 allele and increased levels of Ass1-42 peptide pose a high risk for developing dementia. On the other hand, the expression of apolipoprotein http://bjp.rcpsych.org/math/epsi.gif

2 allele and atypical karyotypes reduce the risk of developing dementia. This study showed that the age of onset of dementia among Down syndrome patients may be influenced by factors other than the overexpression of amyloid precursor protein. (APP) [Nicole Schupf, (2002)] very recent study has revealed another gene besides the one controlling the expression of APP as also contributing to Alzheimer's type dementia in downs syndrome patients. This study by Wellington et.al 2007 has showed that a gene on chromosome 21, which is involved in the control of cell cholesterol, may be contributing to the onset of dementia among DS patients. Their finding is supported by the fact that the cholesterol transporter ABCG1 controls the cellular distribution of Amyloid precurssor protein. The increase in ABCG1 also increases the APP in both the amyloidogenic and nonamyloidogenic pathways. The researchers found that this protein which controls the cholestrol metabolism is high in the brain of down syndrome patients suggesting a definitive role for this gene in alzheimers type dementia and downs syndrome. This is reportedly a new breakthough in our genetic understanding of the downs syndrome related dementia. This discovery is expected to provide new ways of looking at pharmacogenetic interventions for dementia among downs syndrome patients. [Wellington et.al, (2007)]

Some studies have focussed on the homocysteine metabolism and its effect on down syndrome patients. It has been reported from earlier research that plasma levels of homocysteine play a huge role in the development of cardiovascular disease and alzheimers type dementia. [Brosnan et.al, (2004)] a more recent study examined the effect of homocysteine levels on IQ among downs syndrome patients. This itlaian study determined and classified the IQ levels of 131 patients with downs syndrome based on the DMS 4 criteria. The researchers documented various factors such as age, vitamin B12 levels, folate, homocysteinaemia (t-Hcys) and applied regression analysis to study their combined effects. Statistical analysis revealed that IQ among DS patients was considerably lower among those who had t-Hcys levels greater than 7.5 µmol/l. Similar observation was also noted for those who were carriers of methylenetetrahydrofolate reductase 677 T (MTHFR 677T) and transcobalamin 776 G. alleles. In particular, it was derived that for those patients with a combination of MTHFR 677T and transcobalamin 776 G. allele, there was a greater risk for IQ < 40 which was the mean IQ for the study group. Thus genetic abnormalities that result in defective remythylation of homocysteine, an important non-protein plasma amino acid, is a contributing factor for the low IQ among down syndrome patients. [J-L Gueant2 et. al, (2005)]

Cognitive Functioning and Dementia

2001 study at the university of Guelph, Ontario, Canada has shown that the level of cognitive functioning may have implications for the onset of dementia among downs syndrome patients. The base for the research was the accepted theory that higher education implies greater 'synaptic reserve'. Earlier studies among healthy population has revealed that many years of education have an effect of slowing down the onset of Alzheimer's. Therefore in this study the researchers compared DS patients exhibiting symptoms of dementia and those without such symptoms and correlated them with other factors such as levels of education, recreational activities, employment, etc. In all, 35 adults subjects in the age ranging between 26 and 67 years were included for the study. All the subjects were periodically observed over 3 years and assessed for their decline based on Neuropsychological tests, reports from caregivers, and the Dementia Scale for Down syndrome. Applying the statistical tool of regression analysis, the researchers found that decline was directly related to cognitive functioning and that higher cognitive functioning implied lesser decline. It was also identified from the study that the level of cognitive functioning was by itself related to the other variables such as education, employment and other activities. Since higher cognitive functioning resulted in lesser decline and since cognitive functioning is by itself positively dependent of the environmental variables (education, employment, hobbies, etc.), there is a direct inference that improving cognitive functioning holds the key to preventing the onset of dementia or at least deferring its onset among the Down syndrome population. [Temple et.al, (Feb 2001)]

One recent research looked at the prospect of improving cognitive performance by restoring the communication channels in the hippocampus region, which is primarily responsible for forming, sorting and storing of memories. The researchers used the mouse model Ts65Dn for their study as it replicates very closely the brain model of a downs syndrome patient. Previous research had reported that too much inhibitory signaling maybe the reason for imbalance in the hippocampus communication. (Kleschevnikow et al., 2004). The researches from Stanford University used two behavioral tests (object recognition task and spontaneous alternation task) along with electrophysiological tests on the brain samples from the mouse model to study long-term potentiation (LTP) for exploring the physiological causes behind learning, retention and recalling. The researchers used young Ts65Dn mice along with wild type mouse (WT) as control subjects. Results showed that Ts65Dn subjects exhibited considerable cognitive impairment. Then the researchers administered minor doses of picrotoxin (PTX), bilobalide (BB), and pentylenetetrazol (PTZ) and continued with the experiments. These drugs have a suppressive effect on the inhibitory signals in the hippocampus. To the surprise of the researchers they found that the Ts65Dn mice treated with the drugs performed considerably better in new 'object recognition' and in particular, those mice treated with PTZ, showed improved cognitive performance even when tested 2 months after the withdrawal of the treatment. This latest research result provides new hope of reversing hippocampal communication problems and thus a new pharmacological approach to dementia. [Sietske Heyn, 2007]

Proactive Screening for Dementia

Some studies have focused on the importance and effect of a proactive strategy towards identification and management of dementia in adults with Down's syndrome. Kalsy et.al 2005 is one recent study, which showed that a proactive screening strategy for adults with intellectual disabilities using neuropsychological and behavioral data obtained from clinical assessment could be an effective way to manage dementia. The researchers from the university of Birmingham also outlined psychological interventions for the different stages of dementia. The results based on 18 subjects who were referred to the program showed that a dedicated psychology service and care provision under a multimodal framework is essential for effective management of patients with DS and dementia.