In most cases, Down syndrome happens when there is an extra copy of chromosome 21. This form of Down syndrome is called Trisomy 21. The extra chromosome causes problems with the way the body and brain develop .Down syndrome is a genetic condition in which a person has 47 chromosomes instead of 46.
• Decrease muscle tone at birth
• Excess skin at the nape of the neck
• Flattened nose
• Separated joints between the bones of the skull
• Single crease in the palm of the hand
• Small ears
• Small mouth
• Upward slanting eyes
• Wide, short hands with short fingers
• White spots on the colored part of the eye
Children may also have delayed mental and social development. Common problems may include:
• Impulsive behavior
• Poor judgment
• Short attention span
• Slow learning
Many different medical conditions are seen in people with Down syndrome, including:
• Birth defects involving the heart, such as an atrial septal defect or ventricular septal defect
• Dementia may be seen
• Eye problems, such as cataracts (most children with Down syndrome need glasses)
• Early and massive vomiting, which may be a sign of a gastrointestinal blockage, such as esophageal atresia and duodenal atresia
• Hearing problems, probably caused by regular ear infections
• Hip problems and risk of dislocation
• Long-term (chronic) constipation problems
• Sleep apnea (because the mouth, throat, and airway are narrowed in children with Down syndrome)
• Teeth that appear later than normal and in a location that may cause problems with chewing
• Underactive thyroid (hypothyroidism)
There is no specific treatment for Down syndrome. A child born with a gastrointestinal blockage may need major surgery immediately after birth. Certain heart defects may also require surgery.

Persons with Down syndrome are living longer than ever before. Although many children have physical and mental limitations, they can live independent and productive lives well into adulthood.
About half of children with Down syndrome are born with heart problems, including atrial septal defect, ventricular septal defect, and endocardial cushion defects. Severe heart problems may lead to early death.
Persons with Down syndrome have an increased risk for certain types of leukemia, which can also cause early death.
The level of mental retardation varies from patient to patient, but is usually moderate. Adults with Down syndrome have an increased risk for dementia. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001992/ For every 800 babies born, one will have Down syndrome. Down syndrome affects people of all ages, races, religious backgrounds and economic situations. Nothing done before or during pregnancy can cause Down syndrome. It occurs in all races, social classes and in all countries throughout the world. It can happen to anyone.

http://downsyndrome.com/history-of-down-syndrome/
• 2 percent of the world's population has Down syndrome.
• According to Wikipedia, 0.1-0.125 % of babies who are born have Down syndrome (1 in every 800-1000 births).
• The overall incidence of Down syndrome is 1:660 newborns, thereby making it the most common genetically diverse configuration in humans. http://wiki.answers.com/Q/What_percentage_of_the_world%27s_population_has_Down_syndrome Fragile X syndrome

• The majority of males with fragile X syndrome demonstrate significant intellectual disability (formerly referred to as “mental retardation”). Disabilities in FXS include a range from moderate learning disabilities to more severe intellectual disabilities.
• Physical features may include large ears, long face, soft skin and large testicles (called “macroorchidism”) in post-pubertal males. Connective tissue problems may include ear infections, flat feet, high arched palate, double-jointed fingers and hyper-flexible joints.
• Behavioral characteristics can include ADD, ADHD, autism and autistic behaviors, social anxiety, hand-biting and/or flapping, poor eye contact,