normal genetic makeup
23 pairs of chromosomes in each cell of the body (22 autosomes and 2 sex chromosomes)
- dominant
- recessive
- x linked inheritance (abnormal gene on female sex chromosome)
down syndrome definition
- The most common trisomy syndrome characterized by one additional chromosome 21;
- There are more than 400,000 people living with Down syndrome in the United States. Life expectancy is ~55-60 years of age
3 genetic mechanisms for trisomy 21
- Non-disjunction (most common) - entire extra chromosome 21 in all cells.
- Mosaic DS - trisomy 21 cells are mixed with a second cell line, usually “normal” (46,XX or 46,XY).
- Translocation DS - part or all of chromosome 21 is translocated to another chromosome, usually 14. The extra chromosome 21 is permanently attached to another chromosome causing a translocation.
risk factors
- no established relationship between DS and diet, drugs, economic status, or life style. - a little more common in families with Alzheimer’s disease
- Non-disjunction increases with maternal age
- If a couple has a child with DS, the risk is higher for the next pregnancy (1/100).
- The risk at age 37 increases to 1/220.
- Risks for amniocentesis results are higher because half to three-quarters of DS fetuses die before birth of natural causes. The risk of DS does not appear increased in siblings of trisomy 21 individuals.
prenatal screening
- maternal serum alpha feto-protein (MSAFP) - not a definitive test, If the MSAFP test is low it suggests the risk of a DS fetus equal to the risk of a woman age 35, and prenatal testing/chromosome studies are suggested if the parents want this information. A positive screening test suggests only that the risk of DS is increased, and the definitive testing of amniocentesis is indicated.
- chorion villus sample (biopsy fetal tissue)
- amniocentesis (removal of small sample of fetal tissue)
- ultrasound/sonogram
- percutaneous umbilical blood sampling (PUBS)
- most accurate method, but highest risk of miscarriage
general clinical features
- Generalized hypotonia
- Atlanto-axial instability/dislocation (mobility of c1 and c2)
- Short and stocky stature
- Small head with shortened oral cavity
- Protruding tongue
- Epicanthal eye folds, upward slanting eyes
- Low-set ears
- Flat nose, wide set eyes with flat bridge
- Extremities are shorter
- Fingers and toes are broader and shorter, wide gap between toes
- Increased risk for visual acuity problems
related health problems
o Cardiovascular abnormalities (40%) o Obesity o Increased risk for respiratory infections o Immune system insufficiency o Thyroid deficiencies o Gastrointestinal problems (reflux) o Increase risk of leukemia
atlanto-occipital instability
Excessive mobility of the joint between the atlas (C1) and Axis (C2) which could lead to cervical subluxation; spinal cord compression caused by subluxation affects ~2% of children with DS. Many children with DS may undergo cervical X-Rays to clear c-spine and allow child to participate in team sports (ie. Special Olympics).
common aspects that affect fine motor skills
- hypotonia
- ligament and joint laxity
- shorter limbs
- medical conditions
- cognitive level
- sensory registration
- hand characteristics: single simian crease, small hands, wrist bones, curved pinky finger (clinodactyly)
developmental delays in all domains of development
- hand grasp
- walking
- language
- personal/social
tx approaches
A good approach to use with a child with Down Syndrome is a “Building Blocks” approach. A good foundation (of the house) is needed for functional use of hands for self-care, fine motor, and play skills.
tx tips
- functionally focused interventions from earliest possible age
- using new abilities to create a bridge with actual participation in specific activities
- active participation!
IQ
IQ of children with Down syndrome is related to their success at implementing functional components and participating in specific activities.
research with feeding
An oral-motor procedure was used to reduce the tongue thrust and allow the food to be swallowed
research with functional developmental profile
Results showed improvements in age-related body function and correlations between specific body functions and participation
research with schools
The strongest predictor of school function was executive functioning (EF) skills, as reported by teachers
