Ultrasound May Prove Easier Test for Down Syndrome
A simple new ultrasound test may be able to rule out the presence of Down syndrome in many fetuses, often eliminating the need for more invasive tests that carry a risk of miscarriage.
The test measures the length of the nasal (nose) bone of the fetus during the twelfth week of pregnancy, Dr. Kypros Nicolaides of King’s College Hospital in London reported in the Nov. 17 issue of Lancet.
Down syndrome, which is characterized by physical and developmental problems as well as mental retardation, is most common in infants born to older women. Amniocentesis is recommended for pregnant women over the age of 35 to look for the extra copy of chromosome 21 that causes the disorder. But the test is associated with a miscarriage rate of about 1%.
Down syndrome babies generally have flat faces and very small noses, Nicolaides said. If the nasal bone shows up on an ultrasound at 12 weeks, he added, the infant is very unlikely to have the disorder and amniocentesis is not necessary.
Fetuses in which the bone does not appear, in contrast, should undergo amniocentesis, even if the mother is younger than 35.
“With the new test, we will improve the detection [of Down syndrome] by two to three times,” he said.
Protein Linked to Both Alzheimer’s, Parkinson’s
A protein that plays a key role in Alzheimer’s disease has now been linked to Parkinson’s disease as well, Duke University researchers reported in the Nov. 14 Journal of the American Medical Assn. The protein is called tau, and it is one of the components of the brain-clogging plaque that is characteristic of Alzheimer’s. Although deposits containing tau are not present in Parkinson’s, the Duke researchers have found that a mutation in the tau gene renders people more susceptible to the disorder.
The tau gene is the first to be linked to late-onset Parkinson’s, the most common form of the disorder, affecting as many as 1 million Americans. A gene called parkin has been associated with a rare form of the disease that strikes people at a much younger age.
People who have the mutated tau gene do not automatically develop Parkinson’s. It does, however, make them more susceptible to the effects of chemicals and other environmental factors that trigger the disease, said Dr. Jeffrey M. Vance of Duke, who led the study.
In a separate report in the same journal, another team from Duke found that at least five other genes may be involved in susceptibility to Parkinson’s.
Studying 174 families from the United States and Australia, a team headed by Dr. Margaret Pericak-Vance found evidence for a strong linkage to regions of chromosomes 5, 6, 8, 9 and 17. The region on chromosome 6 contains the parkin gene, which was not previously suspected of involvement in late-onset Parkinson’s. The region on chromosome 17 contains the tau gene.
Gene Defect Detected in SIDS Cases
Genetics plays a role in sudden infant death syndrome, the heart-rending disorder in which infants die in their sleep from no apparent cause.
Campaigns to prevent infants from smothering by laying them on their backs have sharply reduced the incidence of SIDS, but as many as 2,500 infants still die from it in the U.S. each year.
Dr. Michael Ackerman and his associates at the Mayo Clinic reported in the Nov. 14 Journal of the American Medical Assn. that they found a defect in a gene called SCN5A in the hearts of two of 93 babies who died of SIDS. The gene helps control heart rhythms and defects in it are associated with a disorder called long-QT syndrome, a heart irregularity that can cause sudden death.
Several other genes are also linked to long-QT syndrome, and the team is looking to see if they might be linked to SIDS as well.
Study Identifies Women Tamoxifen Might Help
Taking tamoxifen has been shown to reduce the risk of breast cancer in high-risk women, but it has never been clear which women will benefit the most. A new study indicates that women with one of the two genes that predispose toward breast cancer will benefit from the drug, while those with the other will not.
The genes are called BRCA1 and BRCA2. About 4% to 10% of women with breast cancer have one of the genes, which increase the risk of the disease to near 100%.
As part of a larger study of tamoxifen, Dr. Mary-Claire King of the University of Washington and her colleagues looked at women with one of the genes. They found that, over five years, the risk of breast cancer in women with the BRCA2 gene declined by 62% among those taking tamoxifen, while there was no change in risk among women with the BRCA1 gene. Studies have shown that prophylactic mastectomies produce a nearly 100% decrease in risk in women with either of the genes.
Exploring Secretin’s Value to Autism Patients
Some studies have suggested that the gastrointestinal hormone secretin may be beneficial in treating autism patients, but results of early trials have been mixed, and no one has been able to provide a good explanation for how the hormone might work. New studies by Repligen Corp. reported last week at a San Diego autism meeting, however, indicate that secretin specifically activates neurons in the amygdala, a part of the brain known to be important in social interactions.
Several previous studies have shown that people with autism do not show normal activation of the amygdala when engaged in social interactions, such as recognizing emotions from facial expressions. The researchers do not yet know, however, why some patients appear to benefit from the hormone and others do not. Repligen manufactures a genetically engineered version of secretin and has been sponsoring tests of the hormone in autistic children.
Encephalitis Vaccine May Fight West Nile Virus
A vaccine already approved in the United States for Japanese encephalitis may help protect people from the most severe complications of West Nile virus infections.
Researchers from the University of Texas Medical Branch at Galveston reported the possibility last week at an Atlanta meeting of the American Society of Tropical Medicine and Hygiene.
The virus that produces Japanese encephalitis is a flavivirus, a member of the same family as the West Nile virus.
Tests in hamsters showed that the vaccine did not prevent infection by the West Nile virus but that it did prevent death and the severe encephalitis (inflammation of the brain) that is normally associated with infections. The researchers believe it will have the same effect in humans.
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Medical writer Thomas H. Maugh II can be reached at thomas.maugh@latimes.com.
