Connective Tissue and Down Syndrome

Key Points

• Connective tissue is the tissue that helps hold our bodies together.

• Connective tissue is different in people with Down syndrome compared to others. 

• People with Down syndrome have a higher frequency of several conditions that may be related to differences in connective tissue.

 

What is connective tissue?

The National Cancer Institute  of the National Institutes of Health (NIH) give this definition of connective tissue: “Tissue that supports, protects, and gives structure to other tissues and organs in the body…Connective tissue is made up of cells, fibers, and a gel-like substance.”

 

Why is connective tissue different in people with Down syndrome?

Connective tissue is different in people with Down syndrome because of differences in their genetic makeup. Our genetic makeup is what makes each of us unique. A few terms that are helpful to know are:

• Chromosomes - structures in our cells that are inherited from our biological parents. Most people have 23 pairs (46 total) chromosomes. Chromosomes are made up of proteins and DNA.

• DNA (deoxyribonucleic acid) - a molecule that contains our genetic information.

• Genes - segments of DNA that affect our physical characteristics and body functions.

People with Down syndrome have three (instead of two) copies of the 21st chromosome. Therefore, the function of genes in the 21st chromosome can be different in people with Down syndrome. Collagen  is a protein that is one of the components of connective tissue. There are many types of collagen. Type VI collagen is encoded on a gene on the 21st chromosome. This is one factor that may contribute to differences in connective tissue in people with Down syndrome.

 

What are the effects of this difference?

Musculoskeletal system

While we could not find much research regarding collagen and Down syndrome, most of what we did find discussed the effect of the difference in collagen (or more broadly connective tissue) on the musculoskeletal system, particularly joints and muscles.

It is well recognized that many people with Down syndrome have decreased (low) muscle tone (hypotonia) and/or joint laxity (loose joints). Type VI collagen is needed for our muscles to function. The difference in Type VI collagen seems to contribute to a difference in muscle function including low muscle tone. Similarly, differences in type VI collagen contribute to lax joints due to changes in the ligaments. Ligaments are the connective tissue structures that connect bones to other bones at the joints.

Laxity of ligaments contributes to the following conditions, all of which are more common in people with Down syndrome:

• Subluxation of the patella - abnormal, excessive movement of the kneecap at times leading to dislocation of the kneecap.

• Overpronation and flat feet (pes planus)

• Atlantoaxial instability - abnormal movement of the bones in the neck.

This is just a partial list of possible joint problems associated with lax ligaments.

Other systems

Connective tissue is important in other body systems in addition to the musculoskeletal system. Other conditions that the difference in connective tissue may contribute to include:

• Keratoconus - Keratoconus is an eye condition in which the cornea (the clear part in the front of the eye) becomes thinner and more curved. Differences in collagen contribute to development of keratoconus and, therefore, it is not surprising that keratoconus is more common in people with Down syndrome.

• Hernias - Hernias typically occur when there is a weakness or defect in the abdominal wall or groin and tissue pushes out through the weakness. Hernias appear to be more common in people with Down syndrome. Connective tissue abnormalities can contribute to hernias.

• Varicose veins - Varicose veins are large, dilated veins. Varicose veins appear to be more common in people with Down syndrome. Abnormalities in connective tissue can contribute to the development of varicose veins.

 

Are there treatments for connective tissue differences?

Currently, there are not treatments that correct the differences in connective tissue in people with Down syndrome. However, there are treatments for conditions caused by the differences in connective tissue. For example, there is a treatment to help hold the cornea shape in keratoconus. 

For musculoskeletal problems related to laxity of joints, an assessment by a physical therapist and following an exercise regimen can sometimes help strengthen the muscles around the joints to improve function. Using orthotics (in the shoes) or braces can also sometimes be of benefit. Good nutrition, sleep, and activity can improve overall health and body function.

Surgery to correct joint abnormalities and hernias is available.

Additional information regarding treatments is described in the articles linked in the “What are the effects of this difference?” section above.

 

References

Adult Inguinal Hernia  (National Library of Medicine Continuing Education Activity)

Down Syndrome Related Muscle Hypotonia: Association with COL6A3 Functional SNP rs2270669  (medical journal article)

Etiology of Inguinal Hernias: A Comprehensive Review  (medical journal article)

Hernias  (Cleveland Clinic article)

Musculoskeletal Anomalies in Children with Down Syndrome: An Observational Study  (medical journal article)

Orthopaedic Issues  (Down's Syndrome Association booklet)

Pathophysiology and Principles of Management of Varicose Veins  (chapter from Mechanisms of Vascular Disease: A Reference Book for Vascular Specialists)

The Proteins of Keratoconus: A Literature Review Exploring Their Contribution to the Pathophysiology of the Disease  (medical journal article)