NEW PRENATAL GENETIC SCREEN
CAMBRIDGE--A sophisticated new genetic screening technique allows early prenatal diagnosis of a common form of hydrocephalus, report English researchers.
The new technique involves taking a sample of the chorionic villus in the tenth week of pregnancy and extracting the DNA, which is then analyzed for a genetic mutation that codes for an abnormal variant of a nerve cell protein, called neural cell adhesion molecule(L1CAM). If the protein is defective, because of the genetic mutation, normal neural development is prevented,
Although ultrasound screening is routinely used to screen for X-linked hydrocephalus, it is not truly effective before the 16th week of pregnancy . The new technique can diagnose the condition within ten weeks when termination of the pregnancy may be less problematical, says Susan Kenwrick, Ph.D, Department of Medicine, Addenbrooke's Hospital, Cambridge, England.
The genetic defect was detected in the male offspring of two women whose infants were born with the X-linked form of hydrocephalus, but who had no known family history of hydrocephalus. In both cases, the women again became pregnant, and because they knew they know that the fetuses were male, they requested that the chorionic villus be sampled for evidence of the gene defect.
The samples were taken in the tenth week of pregnancy and neither contained the abnormal DNA sequences, assuring the women that their babies would not be affected by hydrocephalus. Both women subsequently gave birth to healthy boys.
The presence of hydrocephalus in the first two children, with typical symptoms of mental retardation, spastic paraparesis and adducted thumbs was " vital" for the preliminary diagnosis of X-linked hydrocephalus and should prove valuable in the early assessment of similar sporadic cases of the disorder in the future, said Dr. Kenwrick.
The new genetic test is important because it can be used for the early prenatal diagnosis of the disorder not only in the offspring of women known to be carriers of the gene but also in those who are not known to be carriers.
Primary congenital hydrocephalus is a common malformation affecting up to 1 in 1,000 births. The x-linked form is most common. In addition to hydrocephalus, affected boys also develop mental retardation, and spasticity. Female carriers are unaffected.
Dr. Kenwrick's work appeared in The Lancet, v. 345, 1/21/95, pp. 161-162.
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