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Thursday, December 5, 2013
Inherited Disorders and Birth Defects
Chiari 1 Malformation and Spina Bifida
I have Chiari malformation and have just learned that my daughter who is 16 weeks pregnant has abnormal maternal serum test results for spina bifida or Down Syndrome. She is having an ultrasound tomorrow. Could this finding be a result of my Chiari?
As you probably know, Chiari malformations are birth defects affecting the posterior brain and brain stem. There are different types - the most common is Type II where there is a displacement of the medulla oblongata (the lowest portion of the brain stem which joins the spinal cord at the opening of the skull to the spinal column). Most of type II Chiari malformations are associated with spina bifida (open spine) and/or hydrocephalus (water on the brain).
The other type, Type I malformations, may not produce symptoms in infancy, but may have problems arise at a later time, which may include headaches, pain, weakness, sensory problems, etc.
The maternal serum screen your daughter had looks for chromosome abnormalities (like Down syndrome) as well as birth defects, such as spina bifida (also called a neural tube defect). The screening test looks at 3 or 4 types of biochemical products that have been found to be associated with chromosome problems and spina bifida. This blood test is a screening test, not a diagnostic test - it can only tell you about your potential chance or risk to have a baby with spina bifida. It cannot tell you for sure if the baby will have spina bifida.
It is very unlikely that your Chiari malformation is related to your daughter having an abnormal maternal serum screen, except Chiari malformations run in your family and are associated with some type of neural tube defects, such as spina bifida. There is a wide variation of spina bifida, some where the person does not ever know they have a defect until an X-ray is taken of the spine for some other reason. If your daughter has a similar type of defect (potentially meaning that it was inherited from you) or has a genetic susceptibility for these types of defects, and the pregnancy is found to have a similar abnormality, then there is a potential that the abnormal maternal serum screen is related.
Hopefully the ultrasound your daughter had was able to provide some information as to why the maternal serum screen was abnormal. Also, there can be a false positive result on the maternal serum screen as this is a screening test that assesses risk, it is not a diagnostic test.
Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University