Also called Trisomy 21, Down Syndrome usually happens when a baby is born with an extra Chromosome 21 or an extra part of Chromosome 21. This is usually caused by an error in cell division during gestation and alters the course of development, resulting in characteristics commonly associated with Down Syndrome. People with Down Syndrome will have differing levels of disability depending on the extent of the genetic mutation. This additional chromosome can cause differing levels of intellectual disability, as well as a number of physical and developmental malformations and a predisposition for other chronic illnesses. The common physical traits of Down Syndrome include low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the centre of the palm. 

Every individual with Down Syndrome is different and some of them may even possess one of these characteristics to a certain degree or not at all. Down Syndrome is considered as the most common chromosomal condition in Australia. Fortunately, people with Down Syndrome are living longer and healthier lives than they were able to in the past due to continued in-depth research and support systems available to them. Living with Down syndrome can bring challenges, yet many individuals go on to enjoy happy, meaningful, and fulfilling lives.

• Facial features: Flattened facial profile, a small nose with a flat bridge, upward-slanting eyes, and small, rounded ears. 
• Hands and feet: Wide, short hands with short fingers and a single crease across the palm. There is often a larger-than-average space between the first and second toes. 
• Muscle tone and structure: Poor muscle tone (hypotonia) at birth, a short neck, and a tongue that may protrude. 
• Height: Individuals with Down syndrome are often shorter than average.

• Intellectual disability: Typically ranges from mild to moderate, affecting cognitive abilities. 
• Developmental delays: Slower development of gross motor skills, like crawling and walking, and fine motor skills. 
• Language delay: Language development may be delayed, partly due to hearing impairment and other speech delays.
• Heart problems: A higher incidence of congenital heart defects. 
• Vision problems: Conditions like farsightedness, nearsightedness, and strabismus are common. Small white spots on the iris, called Brushfield’s spots, may also be present. 
• Hearing loss: Increased risk of hearing loss due to recurrent ear infections and other issues. 
• Other issues: Gastrointestinal problems, thyroid issues (hypothyroidism), and an increased risk for leukemia and Alzheimer’s disease later in life are also associated with Down syndrome.