Musculoskeletal Effects Of Down Syndrome
Down Syndrome In General
Down syndrome is a chromosomal condition characterized by the presence of an extra copy of genetic material on the 21st chromosome, either in whole (trisomy 21) or part (such as due to translocations).
Down syndrome is diagnosed in two ways, during pregnancy or shortly after birth. The diagnosis is always based on the presence of an extra number 21 chromosome on a karyotype.
Testing that can be done during the pregnancy:
Chorionic Villus Sampling (CVS)
In this procedure, a small amount of tissue is taken from young placenta. These cells contain the foetal chromosomes that can be tested for Down syndrome. The result of the test will give you a picture of the foetus’s chromosomes and the diagnosis of Down syndrome is very straightforward. CVS is usually carried out between the 10th and 12th weeks of pregnancy.
An ultrasound test is a test which uses sound waves to generate a picture or image of the foetus. The main usefulness of ultrasound is to confirm the gestational age of the foetus. Another benefit can also pick up problems of a serious medical nature, such as blockage of the small intestine of heart defects.
Studies showed that there was a strong association between the size of the nuchal translucency and the risk of Down syndrome. This nuchal translucency is a temporary collection of fluid under the skin of the neck. A thickened nuchal translucency (more than 3 mm) on ultrasound may indicate a chromosomal abnormality, of which Down syndrome is the most common.
Maternal serum screening
The maternal serum test measures the amount of substances made by the foetus in the mom’s bloodstream and estimate the risk for the baby to have Down syndrome. The mother’s blood is checked for a combination of different markers alpha – fetoprotein (AFP), unconjugated estriol (uE3) and human chorionic gonadotropin (hCG). In down syndrome, the AFP and uE3 are decreased and hCG is increased in the mother’s blood. These three markers make up the triple test. Sometimes a marker called inhibin A is added, making the “quadruple screen”. The level of inhibin A is increased in the blood of mothers of foetuses with Down Syndrome. Recently was found that another marker called pregnancy-associated plasma protein A (PAPP – A) can also be used. Low levels of this protein are seen in Down syndrome pregnancies.
This procedure is used to collect amniotic fluid, the liquid of the womb. A needle is inserted through the mother’s abdominal wall into the uterus, using ultrasound to guide the needle. This method is usually carried out between the 14th and 18th week of pregnancy.
The diagnosis during birth is done by watching some differences in the baby's appearance. These may include a flat facial profile, an upward slant to the eye, a short neck, abnormally shaped ears, … .
Reduced muscle strength
Bone mass and bone geometry are influenced by growth and muscle development in children and adolescents. This process is further modified by hormonal signals.
Motor function in individuals with Down syndrome is characterized by hypotonia and hyperflexibility, which results in an increased risk of joint dislocation and retarded motor skills.
Hypotonia, decreased muscle tone, has a negative effect on the proprioceptive feedback from muscle and joint sensory structures and can have a detrimental effect on the efficiency of co - contractions and postural reactions.
People with Down syndrome have more joint mobility than the average. The enlarged joint mobility may contribute to the lack of posture control. Together with the failure of co – contraction, it will affect the joint stability.
This joint laxity is found in several parts of the body due to the abnormal collagen found in Down syndrome.
Vitamin D deficiency
There is a damaging effect of vitamin D insufficiency on musculoskeletal health in children and adolescents during the critical time of bone-mass accrual.
Vitamin D is not only essential for normal growth of children, but also for the preservation of the bones. Vitamin D is also important for other functions such as muscle tone, the immune defence and even cancer.
Vitamin D, per oral absorbed through food or created under the influence of sunlight, is a precursor of the hormone 1,25 – dihydroxyvitamin D. The latter stimulates the small intestine absorption and kidney reabsorption of calcium and thus ensures a better bone. Watch the animation of this process in order to understand it better.
In patients with Down syndrome, risk factors, such as inadequate exposure to sun, inadequate vitamin D intake and malabsorption or increased breakdown of vitamin D that accompanies anticonvulsant therapy, contribute to vitamin D insufficiency. Down syndrome patients usually have osteoporosis and fractures as a result of this deficiency.
The accrual of bone mass during childhood is a key determinant of bone health in adulthood, and a low peak skeletal mass is considered an important risk factor for osteoporosis in adult life.
Multivariate analysis showed that Down syndrome was associated with low Bone mineral density, BMD, of the spine. Lack of physical exercise, low muscle strength, insufficient exposure to the sun, low levels of vitamin D and prolonged use of anticonvulsants are all additional risk factors for low BMD.
Some experts hypothesize that the extra copy of chromosome 21 could be responsible for the short stature, skeletal abnormalities and early aging that are seen in patients with Down syndrome.
The goal of physical therapy is to minimize the development of the compensatory movement patterns that children with Down syndrome are prone to develop. Working with their muscles and movements will help children reach some of their motor milestones and will prevent them from developing problems, such as bad trunk posture and gait problems.
Children with Down syndrome typically learn to walk with their feet wide apart, their knees stiff and their feet turned out. They do so because hypotonia, ligamentous laxity and weakness make their legs less stable. Physical therapy should start with teaching the child with Down syndrome the proper standing posture when he is still very young. So, feet positioned under the hips and pointing straight ahead with a slight bend in the knees. With appropriate physical therapy, gait problems can be minimized or avoided.
Children with Down syndrome typically learn to sit with a posterior pelvic tilt, trunk rounded and the head resting back on the shoulders. Physical therapy must teach the child the proper sitting posture by providing support at the proper level even before the child is able to sit independently. Appropriate physical therapy can minimize problems with trunk posture.
This is an example of a training program to improve muscle strength with progressive resistance training. Progressive resistance is a feasible and safe fitness option for people with Down syndrome to improve upper – limb muscle performance. Longer training programs may be required to improve leg strength and activity.
Various other studies illustrate also positive effects on motor skills. Without physical therapy, a child with Down syndrome could end up having orthopaedic problems later in life from using their muscles incorrectly.
The importance of early intervention should be emphasized. Physical therapy at an early age strengthens the muscles, enabling the children with Down syndrome to keep their body in proper alignment and prevent future health problems.
- WIKIPEDIA, http://en.wikipedia.org/wiki/Down_syndrome , consulted on December 14, 2011. (level of evidence: 2)
- MEDLINE PLUS, http://www.nlm.nih.gov/medlineplus/ency/article/002330.htm, consulted on December 14, 2011. (no references found on site)
- ABOUT.COM, http://downsyndrome.about.com/od/diagnosingdownsyndrome/a/ Diagnosisess.htm , consulted on November 22, 2011. (level of evidence: 2)
- PRENATAL SCREENING FOR DOWN SYNDROME, http://www.ds-health.com/prenatal.htm, consulted on December 14, 2011. (level of evidence: 2)
- VAN EMPELEN R, Kinderfysiotherapie, tweede druk, 2008. (level of evidence: 1)
- HAWLI, Y., Endocrine and musculoskeletal abnormalities in patients with Down syndrome, 2009. (level of evidence: 1)
- MEDLINE PLUS, http://www.nlm.nih.gov/medlineplus/ency/article/003298.htm , consulted on November 29, 2011. (level of evidence: 2)
- DOWN SYNDROME: HEALTH ISSUES, http://www.ds-health.com/ortho.htm, consulted on November 14, 2011. (level of evidence: 2)
- NIEUWSBRIEVEN, http://www.cri.be/b/letters/1034803024.htm, consulted on November 26, 2011. (level of evidence: 2)
- VITAMIN D AND CALCIUM ANIMATION, http://www.youtube.com/watch?v=JwPVibQ6_3Y, consulted on November 26, 2011. (no references found on site)
- WINDERS, P.C., The goal and Opportunity of Physical Therapy for Children with Down Syndrome, 2001. (level of evidence: 2)
- SHIELDS N., Effects of a community – based progressive resistance training program on muscle performance and physical function in adults with down syndrome: a randomized controlled trial, 2008. (level of evidence: 1)
- EARLY INTERVENTION SUPPORT, http://www.earlyinterventionsupport.com/diagnosis/List/Down-Syndrome.aspx , consulted on November 29, 2011. (no references found on site)