Chris Willocks 2007 1

Year 10 ScienceHealth and disease

Genetic disease:

Down’s syndrome

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Down’s Syndrome

What are some traits of Down’s syndrome?

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Down’s syndrome

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Down’s syndrome traits• low muscle tone • eyes may have an upward and outward slant • nasal bone can be underdeveloped• the tongue can have less space and protrude • legs and arms are often shorter • hands are short and stubby with a single crease across

the palm • genitals may be small • hair is sometimes fine and straight • teeth may be slightly smaller and do not appear in

normal ‘order’ • delay in sitting, crawling, talking, toileting• most have mental retardation in the mild (IQ 50–70) to

moderate (IQ 35–50) range• can have heart defects, digestive disorders etc

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Down’s syndrome karyotype

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Trisomy 21

• Down syndrome disorders are based on having too many copies of the genes located on chromosome 21.

• This leads to an overexpression of the genes

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Incidence of Down syndrome

• Occurs in all races• One in every 600 to 700

babies born • Probably more Down

syndrome babies are conceived, but many miscarriages are due to a chromosome error

• The number of children born with Down syndrome increases as mothers become older.

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Effect of Mother’s age

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Effect of mother's age

• Mothers in their 40's are much more likely to have a child with Down's syndrome than younger mothers.

• The eggs produced during ovulation are as old as the mother.

• There is a greater chance for older eggs to have problems that lead to nondisjunction.

• Younger mothers (<35 years) who smoke are at an increased risk of having children with Down syndrome.

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Development in childhood• Development is variable • Delay in sitting, crawling, talking• It is not possible to predict their

capabilities • Early intervention programs from

birth are useful• Success at school can vary greatly • It is common for children with Down

syndrome to need speech therapy to help with expressive language.

• Fine motor skills are delayed and often lag behind gross motor skills

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Intervention programs

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Life span• The average life expectancy of a person with

Down syndrome is 55+, with some people living into their 80's.

• In 1960 60% of children died before 5 years of age

• Medical research has totally changed the quality of health of people with Down syndrome.

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Relationships• People with Down syndrome have feelings just

like anyone else in the community.• Respond to positive expressions of friendship

• Are hurt and upset by inconsiderate behaviour.

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Ageing parents

• What happens to them as their parents age?

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Sex and marriage• People with Down syndrome date, socialise and

form on-going relationships • In the past it has been unusual for people with

Down syndrome to marry• Females with Down syndrome menstruate and

have been recorded as mothers. There is a 50% chance that their child will have Down syndrome.

• A proportion of males who have Down syndrome will produce sperm and cannot be considered sterile.

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Detecting Down’s

Ultrasound may detect abnormal foetal growth

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Foetal development

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Amniocentesis

Cells from the amniotic fluid are karyotyped