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The Continued Mystery of Congenital Scoliosis
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Posted on: 08/26/2009
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Sometimes babies are born with defects or anomalies like missing vertebral bones, only half of a vertebral bone formed, fused vertebral bones, and/or fused ribs. These defects result in curvature of the spine called congenital scoliosis. Any time this happens, the parents wonder, What did I do wrong? How did this happen?
At this point, scientists still don't know the etiology or cause of congenital scoliosis. In this report, Dr. Robert N. Hensinger from the Pediatric Orthopaedic department of the University of Ann Arbor, Michigan presents a review of the information known so far about this condition.
Let's go right back to the moment of conception. The sperm meets the egg, penetrates, and fertilizes it. Now the cells begin to divide rapidly. By day eight, the beginnings of the spine are already being formed. Whatever causes the vertebrae to develop abnormally occurs early on before the cartilage or bone are even formed. This is the period of embryonic growth referred to as prenatal vertebral growth. It takes place between the third and the fifth week of life. The tiny structures that will eventually be vertebral bodies are called somites.
Shortly after the formation of somites, vertebral defects begin to occur. The developing child in the womb is only about 30 days old and seven to 13 millimeters long from the top of the head to the bottom of the spine (crown to rump). In order for each vertebral bone to form properly, there must be enough blood supply carrying nutrients and oxygen to the area. Without this, malformations occur. The lack of blood vessels (arteries) to each somite or segment prevents the bones from dividing into segments that will become individual vertebral bodies. So, oxygen is important.
What causes a lack of oxygen? Too much carbon monoxide. What causes too much carbon monoxide? Probably some environmental factor like exposure to chemicals but at this point, scientists know much more about the what (what happens) than the why (why it happens). Studies using mice have helped reveal the way the deformities develop, just not always the factors linked with the deformities.
It is thought that there are two main risk factors: environment and genetics. Besides exposure to possible chemicals such as industrial solvents, there could be exposure to cigarette smoke, alcohol, anticonvulsant medication, too much vitamin A, and a lack of folic acid (one of eight B vitamins). The discovery that a lack of folic acid during pregnancy causes vertebral and spinal cord defects resulted in flour, prenatal vitamins, and other foods being fortified with this essential vitamin. The number of cases of spina bifida went down dramatically after that.
That's as much as we know so far on the environmental side of things. What about genetics? Could congenital scoliosis be an inherited condition? Are there specific genes involved and gene mutations that change how cells are regulated to form the spine?
Again, using mice as a model to help explain what went wrong, scientists have found genes that do regulate the embryonic formation of cells that normally lead to the development of the spinal bones. One particular family of genes (the notch family) has even been identified in humans as responsible for early embryonic development of the spinal column. Another set of genes called the Hox genes are involved in the formation of the skeleton. Research with mice is ongoing to discover the cause and connections between mutations of Notch and Hox genes and vertebral or other bone malformation.
Sometimes there's more than just the spine involved. Other problems present but not visible might not be readily apparent, so it's a good idea to examine the child for hidden defects and deformities. Children with several problems along with congenital scoliosis may have a well-known and recognized syndrome. Some of these syndromes include Klippel-Feil syndrome, Sprengel's deformity, Goldenhar syndrome, and the VACTERL, which stands for the various problems involved (V for vertebral defects, A for anal atresia, T for tracheo-esophageal fistula and atresia, R for renal deformities, and L for limb defects).
Not only are there vertebral anomalies, but deformities can occur at the top of the spine at the foramen magnum (hole for the spinal cord) and at the bottom of the spine sacrum. The bottom portion of the brain inside the skull is called the cerebellum. The cerebellum is connected directly to the spinal cord. The bottom of the cerebellum sits on the base of the cranium (skull) and the spinal cord goes down through the foramen magnum. Narrowing of the foramen magnum or the opposite problem (too large of a hole) can cause problems. Too small of an opening puts pressure on the spinal cord. With too large of a hole, the cerebellum starts to slip down through the hole. This is called a Chiari malformation. That can occur at the upper portion of the spine.
At the bottom end of the spine, sacral agenesis can be another problem. Complete sacral agenesis means there is no sacrum -- it just doesn't form. In less severe forms, only half of the sacrum is present or there may be a part missing on both sides. Depending on the type of sacral agenesis that is present, there may be bowel or bladder problems as well. Again, no one is exactly sure why this deformity occurs. There's a link between mothers with diabetes and children born with sacral agenesis. But what the connection is to diabetic-related insulin deficiency (if there is one), remains a mystery.
As you can see from this summary of Dr. Hensinger's publication, there are more unknowns than knowns in the understanding of congenital scoliosis. Efforts to find environmental or genetic links have only been partially successful in explaining what went wrong and why. Correcting some vitamin deficiencies has helped but the problem still occurs. As with many unusual physical problems, it's likely that several (or even many) factors combined together result in this potentially serious condition. Future research will continue looking for answers to this puzzling problem.
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References:
Robert N. Hensinger, MD. Congenital Scoliosis. Etiology and Associations. In Spine. August 2009. Vol. 34. No. 17. Pp. 1745-1750.
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*Disclaimer:*The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic. |
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