Early Detection of Cognitive Decline in Intellectual Disability: A Guide for Neurorehabilitation Professionals

Psychologist Alonso Donoso López presents the benefits of neurorehabilitation for the early detection of cognitive decline in intellectual disability.

Executive summary with the key points of this article:
1. Premature aging in people with intellectual and developmental disabilities typically begins at age 45.
2. Neurorehabilitation harnesses brain plasticity to slow decline.
3. Tools such as CAMDEX-DS and NeuronUP are critical for establishing baselines.

Introduction: Why does premature aging occur in intellectual disability?

One of the main characteristics of people with intellectual disability is the well-known premature aging process in this population. This population begins the aging process at around 45 years of age (Berjano, E., & García, E. 2010).

The reason for this premature aging can be explained by several notable causes: a combination of biological and environmental factors, such as molecular genetic dysfunction, increased oxidative stress, chronic low-grade inflammation, comorbidity and associated medical factors, and environmental and psychosocial factors. 

Early detection of this process can lead to improvements in the person’s functioning and help identify the support plan needed to ensure the best possible quality of life. 

Early intervention for cognitive decline in intellectual disability

The importance of early detection of cognitive decline

From the moment of birth, or even earlier, it is important to be able to detect whether there is any type of anomaly that could significantly affect a person’s development. This will partly determine the possible causes affecting their aging process and the possible diseases that may develop in the future. 

The origin of intellectual disability may involve multiple causes and occur at different stages: prenatal, perinatal, and postnatal. According to studies, 25% of people with intellectual disability have an unknown etiology, although it may have a genetic origin. 

It is important to highlight and consider the person’s characteristics and level of intellectual disability (mild, moderate, severe, or profound), support needs, and level of adaptive functioning. Intellectual disability associated with a syndrome is not equivalent to intellectual disability that appears as an isolated condition, since their developmental implications differ. 

Syndromic intellectual disability is associated with dysmorphic features, physical and congenital anomalies, and possible behavioral problems. Intellectual disability not associated with a syndrome presents intellectual disability as the only evident characteristic, measurable with an intelligence and adaptive behavior test. 

We must not forget that a person’s development is intrinsically linked to the interaction between their abilities and the resources in their environment. Under the paradigm of Schalock and Verdugo (2002), early stimulation and the promotion of healthy habits are not merely preventive measures, but essential strategies for improving quality-of-life dimensions. 

An individualized support system aligned with the person’s needs throughout all stages of life not only promotes a healthier, more positive aging process, but also acts as a protective factor that reduces the likelihood of morbidity, promoting the highest possible level of autonomy in adulthood (Schalock & Verdugo, 2002). 

For this reason, prevention plays an important role in the support plan for a person with intellectual disability, regardless of their age or associated syndrome. 

Warning signs of cognitive decline in intellectual disability

The aging process is the same in people without disabilities and people with intellectual disabilities; however, the latter group does present certain characteristics that should be considered (Vázquez de Prada et al. 1992).

People with intellectual disabilities may develop neurodegenerative diseases, such as Alzheimer’s disease or dementia with Lewy bodies, among the most common conditions. 

Based on daily clinical experience, the most notable symptoms in the presence of possible cognitive decline tend to include:

• impaired comprehension of verbal instructions and short- and medium-term memory,
• difficulty sustaining attention,
• spatiotemporal disorientation,
• behavioral changes,
• functional errors when performing a previously consolidated task,
• incontinence,
• loss of appetite,
• depressive symptoms,
• anxiety symptoms,
• hallucinations and delusions. 

It is important for the professional (psychologist, neuropsychologist, psychiatrist) to conduct a thorough differential diagnosis and a complete physical and psychological examination, first ruling out whether the symptoms may be explained by another organic cause, such as a urinary tract infection, or by a psychological cause, such as a depressive disorder, adjustment disorder, anxiety disorder, or psychotic disorder. Other pathological processes that may signal decline in the person should also be considered, such as sleep apnea, thyroid disorders, vitamin B12 deficiency, metabolic diseases (kidney disease, diabetes), vision or hearing loss, heart disease, or seizure disorders, among others. 

Prevalence of Alzheimer’s disease in Down syndrome

We know that, within intellectual disability, certain syndromes carry a higher likelihood of clear cognitive decline. The aging process in people with intellectual disability is not uniform, and the etiology of the disability is particularly relevant. According to Fundación Iberoamericana Down 21 (n.d.), people with Down syndrome over 60 years of age have a 75% probability of developing Alzheimer’s-type disease, which may appear at younger ages, with the average age being 55. 

The prevalence of Alzheimer’s disease in people with intellectual disability without an associated syndrome is the same as in the population without intellectual disability. However, there is an additional burden: people with intellectual disability do not usually report memory complaints or attention problems, which significantly complicates the detection of symptoms of decline. 

Therefore, establishing a cognitive assessment with a prior baseline helps us detect any symptoms associated with cognitive decline at an early stage. Cognitive neurorehabilitation in the context of intervention gives us the opportunity to observe these changes as the patient’s condition evolves. 

At Fundación AMÁS—an organization created by family associations (AFANDEM, Adfypse, and Aspandi) in the Community of Madrid that defends and promotes the rights of people with intellectual and/or developmental disabilities and those of their families—we establish criteria for assessing possible cognitive decline according to age, etiology, and other relevant factors:

• At age 35: Down syndrome, cerebral palsy, tuberous sclerosis, epilepsy, severe mental disorder, autism, and people with extensive support needs or communication difficulties. 
• At age 45: Steiner syndrome, fragile X syndrome, Williams syndrome, Prader-Willi syndrome, Rett syndrome, and acute mental disorder.

How neurorehabilitation facilitates the early detection of cognitive decline in intellectual disability

Neurorehabilitation represents a strategic opportunity for preventing cognitive decline, grounded in the nervous system’s capacity for plasticity.

Robust scientific evidence confirms that cognitive training strengthens neural circuits, based on the principle that neurons that fire together strengthen their connection (Hebb, 1949). This capacity for functional reorganization is effective even after brain injury, when interventions based on intensive use and specific training have been shown to significantly improve cognitive and motor difficulties (Taub et al., 1993).  

Benefits of neurorehabilitation for early identification

One of the concepts that has significantly shaped the understanding of neurorehabilitation is the concept of brain plasticity. 

In the late nineteenth and early twentieth centuries, Santiago Ramón y Cajal proposed that the brain can undergo changes and reorganize itself. This approach was consolidated by Donald Hebb (1949), who described the activation of nearby neurons and their modification when new learning occurs. People with intellectual disabilities also demonstrate this adaptive capacity of the nervous system. 

In this regard, cognitive neurorehabilitation is an effective tool for enhancing executive functions and specific cognitive processes, promoting greater functional autonomy (Vicari, 2006). In contrast, clinical evidence emphasizes that the absence of cognitive stimulation and rehabilitation programs may be a risk factor associated with cognitive decline (Moreno, Castillo, and García, 2023). This vulnerability became particularly evident in the context of isolation, such as during the COVID-19 pandemic, when the lack of direct intervention accelerated processes of decline that might have been slowed under conditions of continued activity (Courtenay & Perera, 2020). 

Successful cases of cognitive assessment and rehabilitation in Down syndrome

At Fundación AMAS we are committed to preventing decline by using digital activities from the neurorehabilitation platform NeuronUP. In our experience, using programs of cognitive stimulation exercises, we have seen how it is possible to detect decline at an early stage, facilitating intervention and treatment before a diagnosis, speeding up the relevant testing, and raising awareness appropriately among both professionals and the families involved. 

Below, we detail (Figure 1) a case showing the progression of a 60-year-old person with Down syndrome and their decline following the onset of Alzheimer’s-type dementia diagnosed in February 2024. 

In addition, the following graph (Figure 2) shows the benefits offered by NeuronUP scheduled activities in terms of learning and brain plasticity for a 53-year-old person with Down syndrome. 

Cognitive assessment tools and strategies for cognitive decline in Down syndrome

Preventing cognitive decline plays a key role in improving quality of life for people with intellectual disabilities and their families. However, it is not the only factor to consider in intervention: an annual assessment, or one every 6 months for more vulnerable individuals, will help us make the necessary adjustments and determine the person’s functional status at that point in relation to others, as well as observe whether there is a pattern of decline in neurological and psychological functioning. 

Standardized tests may not optimally reflect the cognitive profile of people with intellectual disabilities, making it essential to complement the assessment with adaptations and a qualitative analysis of performance.

Clinical assessment is conducted using the adapted CAMDEX-DS (Cambridge Examination for Mental Disorders of Older People with Down’s Syndrome or with Intellectual Disabilities). This scale is essential for establishing an accurate differential diagnosis, as it makes it possible to triangulate information obtained directly from the individual with clinical observations from family members and professionals who know the person well (Ball et al., 2013). Its implementation is decisive for identifying early signs of cognitive decline and distinguishing them from the baseline limitations associated with intellectual disability. 

We must also remember to assess the person’s intellectual level using the WAIS IV (Wechsler Adult Intelligence Scale—Fourth Edition) or the K-BIT (Kaufman Brief Intelligence Test), since the results of cognitive assessment may be biased when comprehension and expressive language skills are low. 

Knowing the person with intellectual disability for at least 6 months also helps avoid these biases in the results. 

Conclusions

It seems clear that appropriate neurocognitive stimulation gives the brain an opportunity to slow, insofar as possible, the early decline that is so commonly associated with intellectual disability. 

On the other hand, the increased life expectancy of people with intellectual disabilities is accompanied by the emergence of other diseases that accumulate silently over time. A thorough understanding and analysis of possible comorbid conditions that may arise in different neurodevelopmental disorders is crucial for the possible and appropriate treatment of symptoms. 

In my view and based on my experience, prevention begins during the prenatal, perinatal, and postnatal periods when, as we know, epigenetics plays an important role in a person’s development. From early stimulation to maintaining healthy sleep and eating habits, inclusive social relationships (with the person with intellectual disability being present, participating, and contributing), and physical exercise, these measures can improve the quality of life and functioning of people with intellectual disabilities. 

Neurorehabilitation offers benefits both in the early detection of cognitive decline associated with the aging process and decline resulting from disease, as well as in delaying its onset. 

References

• American Psychiatric Association. (2022). Diagnostic and statistical manual of mental disorders (5th ed., text rev.; DSM-5-TR). American Psychiatric Association. 
• Ball, S. L., Holland, A. J., Huppert, F. A., Treppendahl, C., y Watson, P. (2013). CAMDEX-DS: Cambridge examination for the assessment of mental disorders in adults with Down syndrome or intellectual disability (S. Esteba Castillo, T. Fernández-Turrado, y R. Novell-Alsina, Trads.). TEA Ediciones. 
• Berjano, E., & García, E. (2010). Intellectual disability and aging: A social and educational problem. 
• Courtenay, K., & Perera, B. (2020). COVID-19 and people with intellectual disability: Impacts of a pandemic. Postgraduate Medicine, 132(6), 487–489. 
• Dennis McGuire, Brian Chicoine. (2009) Mental wellness in adults with Down syndrome
• de Down. Santander. Fundación Iberoamericana Down21.
• FEAPS. (2007). Aging in people with intellectual disabilities and extensive support needs (Day Care Notes No. 3). Confederación Española de Organizaciones en Favor de las Personas con Discapacidad Intelectual. 
• Hebb, D. O. (1949). The organization of behavior: A neuropsychological theory. Wiley. 
• Javier García-Alba, Susanna Esteba-Castillo, Marina Viñas-Jornet. (2018) Neuropsychology of intellectual disability of genetic origin. Madrid. Síntesis. 
• McGuire, D., & Chicoine, B. (2009). Mental wellness in adults with Down syndrome. Fundación Iberoamericana Down21 
• Moreno-Noguez, M., Castillo-Cruz, J., & García-Cortés, L. R. (2023). Risk factors associated with cognitive decline in older adults: A cross-sectional study. Revista Médica del Instituto Mexicano del Seguro Social, 61(Supl. 3), S395–S406. https://revistamedica.imss.gob.mx/index.php/revista_medica/article/view/5070
• Schalock, R. L., & Verdugo, M. A. (2002). Handbook on quality of life for human service practitioners. American Association on Mental Retardation.
• Taub, E., Miller, N. E., Novack, T. A., Cook, E. W., 3rd, Fleming, W. C., Nepomuceno, C. S., Connell, J. S., & Crago, J. E. (1993). Technique to improve chronic motor deficit after stroke. Archives of Physical Medicine and Rehabilitation, 74(4), 347–354. 
• Vicari, S. (2006). Neuropsychological development in persons with Down syndrome. American Journal of Medical Genetics Part C: Seminars in Medical Genetics, 142C (3), 163–173. https://doi.org/10.1002/ajmg.c.30101

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