In humans, when an egg is fertilised with sperm, 46 chromosomes are typically created. Down’s Syndrome is caused by an extra copy of Chromosome 21. Around 2% of these will have two or even three copies of Chromosome 21, a condition known as Mosaic Down’s Syndrome. People who have Down’s Syndrome usually have distinctive facial features associated with the condition, in particular, eyes that slant upwards at the outer edges. They are often smaller than average in terms of height and their hands and feet. In terms of learning, Down’s Syndrome can affect a person’s abilities with speaking, literacy, maths, and memory. Many people with Down’s Syndrome have support in education, working or organisation.
This rare condition is caused by a person being born without at least 25 specific genes that are usually present in Chromosome 7. People with Williams Syndrome usually have ‘elfin’ facial features and often an excitable, outgoing and highly empathetic disposition. They can be very interested in other people, extremely friendly and have extraordinary memories. They can have difficulty with learning, and be slower in developing skills than other people.
Rett Syndrome is caused by a mutation on a gene of the X Chromosome. The majority of people affected by the condition are female, because females have two X chromosomes while males have one X and one Y. It is a neurological and developmental condition, so despite being born with Rett Syndrome, people with it are actually affected more as they grow. Their abilities with movement and communication can decrease over time or be lost altogether.
Prader-Willi Syndrome is caused by a fault in Chromosome 15, which can affect appetite and growth. It is not hereditary. People with the condition can have extreme appetites, as well as difficult behaviour in an attempt to fulfil their overwhelming desire to eat. Most people with Prader-Willi Syndrome also have some level of learning difficulty or disability. As children they usually develop more slowly, both physically and in terms of academic and social skills, than other children.
Autism Spectrum Disorder and Asperger’s Syndrome
Autism is not a learning disability in itself. In fact, many people with autism have extremely high intelligence, but around half of people with the condition do have a learning disability. Autism is a neurological disorder whose cause is not clear, but researchers generally agree that it is to do with the genetic makeup of a person’s brain, and can be hereditary. It can affect a person’s abilities to form an understanding of what they are learning. Around 1% of people have autism.
Asperger’s Syndrome is a form of autism that affects a person’s abilities with social interaction and can cause people to have repetitive behaviour or fixations. Learning disabilities are rare in people with Asperger’s and they often have above-average intelligence. This, along with their tendency to become fixated on a subject, can actually help them to have successful careers at school and work, but they can struggle with the social side.