A disability, put simply, is an impairment that disrupts the performance of executive tasks and ADLs (activities of daily life). Disabilities can be said to physically and/or mentally impact an individual's independence and quality of life. Diseases and disorders often act as precursors to the disability in question. A contextually relevant example would be of either the disease hemophilia or thalassemia - 2 blood-related disorders.

There are also diseases and disorders, such as multiple sclerosis, which lead to disabilities. Multiple sclerosis is a CNS (central nervous system) related chronic condition where the body's immunity eats away at the sheath of myelin, a protective coating, around nerve fibers; this can then lead to vision impairments and physical disabilities.

While speaking about disability, 3 broad categories must be considered -

1. Sensory - For example, vision and hearing impairments.

2. Physical - For example, muscular dystrophy/dwarfism/loss of limb.

3. Cognitive & Intellectual - For example, autism /dyslexia/dyscalculia/dysgraphia.

Each of these differs in its impacts on an individual. A loss of sensory ability would cause the deliberate heightening of other senses to compensate for the loss of [an irreplacable] function. On the contrary, scientific development and inclusive measures have aided people impacted by sensory disabilities to regain some lost function. A common example would be a cochlear implant - a neuroprosthesis that has been created to stimulate the cochlear nerve and hear to a degree that aids in comprehension and communication (accompanied by speech therapy / other measures like lip-reading). A cochlear implant works best when fitted as soon as the hearing impairment is diagnosed and though the cost can sometimes be prohibitive, is the best option available today. Hearing aids typically amplify all sounds in the environment and can cause some discomfort. They work well for a person with residual hearing. In early intervention, a cochlear implant is definitely recommended followed by the required speech therapy. The mechanism of a cochlear implant is to reroute sound signals, that reach us in the form of vibrations, to the cochlear nerve which then sends these signals, as electrical impulses, to the brain to interpret. This delicate transmission of information, from vibrations to impulses, is carried out by a cochlear implant - although evidently not as efficiently as a well-functioning ear. A sound processor that picks up on vibrations and frequency changes, i.e. sound changes, in the environment uses a transmitter that sends these signals to a stimulator/receiver implanted under the skin surgically. The receiver and stimulator pass on this information electrically - to electrodes implanted in the cochlea which then perform the function of cochlear nerve stimulation. this process restores, in most cases, some hearing. A diagram of this is seen in Image 1.

With enough practice, most patients with hearing loss/deafness learn visual cues, lip-reading, etc, and are able to regain sufficient communication skills.

A physical disability usually refers to the loss or degeneration of a body part; this often leads to lacking sensorimotor and locomotive ability. Physical disability, being more visible to the public, often leads to better understanding and availability of treatment. A common example would be of replacing a lost limb with a prosthetic - today, prosthetics that replace the lost limb are being created as they work not only at a degree that allows for physical restoration but also sensory-tactile restoration. This is not to say that physical disabilities, in any way, are easier on an individual. Muscular dystrophy refers to a group of hereditary diseases that lead to the atrophy of musculature over the years, eventually leading to the patient having to use a wheelchair. This loss of muscular function is not only severely painful but also results in loss of most praxis and executive functions. A comparison of the bicep muscle of 2 individuals is shown in Image 2 - one of an individual with and another without muscular dystrophy.

Even breathing, swallowing and other basic motor functions are lost. Lastly, the lifespan of the patient is inevitably shortened despite intervention.

Cognitive and Intellectual disabilities

This broad spectrum of cognitive and intellectual disabilities refers to a condition where a 'person has certain limitations in mental functioning and in skills such as communication, self-help, and social skills.' Such limitations in development, in turn, lead to a lack of comprehension, awareness, communication, behavioral skills and judgment compared to children/adults of the same age. Some of these disabilities can also be situational or temporary. Such disabilities can be diagnosed by looking at below-average IQ scores, maladaptive behavior (for example, self-harm, aggressive behavior), lack of communication (verbal and non-verbal, such as eye contact during speech), and prolonged periods to perform basic executive tasks and learn praxis functions. A common example is dyslexia - 'a learning disorder that involves difficulty reading due to problems identifying speech sounds and learning how they relate to letters and words (decoding)'. People with dyslexia show different symptoms at different stages of life - as a toddler not being able to comprehend or read nursery rhymes to an adult being unable to perform rigorous reading and writing.

These categories of disabilities have been made for convenience in understanding variation between forms of disability; however, there are visible overlaps in these classifications as many diseases, disorders, and disabilities impact over 1 constituent of our being. For instance, Down syndrome - 'a chromosomal condition that is associated with intellectual disability, a characteristic facial appearance, and weak muscle tone (hypotonia) in infancy.' Down syndrome affects an individual's physical and cognitive function - with distinctive facial features and their cognitive and intellectual abilities stunted. This results in age-inappropriate behavior at times.

Down syndrome, 95% of the time, is caused by a chromosomal condition referred to as Trisomy 21 where the 21st chromosome undergoes non-disjunction, i.e. the chromosomes fail to separate in meiosis. This can happen when the homologues do not separate in Anaphase I or when the sister chromatids don't separate in ANaphase II. In all simplicity, Down Syndrome is a byproduct of an extra chromosome - as shown in a karyotype in Image 3.