Downsyndrome.com

PARIS — An absent nasal bone at 11-14 weeks’ gestation is strongly related to the presence of chromosomal defects, Dr. Kypros H. Nicolaides reported at the 13th World Congress on Ultrasound in Obstetrics and Gynecology.

Among fetuses with absent nasal bone, the likelihood of Down syndrome can be further delineated by racial/ethnic group, gestational age, and the degree of nuchal translucency, said Dr. Nicolaides, director of the fetal medicine center at King’s College, London.

Of 3,788 fetuses scanned by ultrasound at 11-14 weeks’ gestation, the nasal bone was absent in 2.8% who were chromosomally normal, 66.9% with trisomy 21, and 33.0% with other chromosomal defects.

Among the 3,358 chromosomally normal fetuses, the likelihood of having an absent nasal bone differed significantly by the mother’s ethnic origin, ranging from 2.5% of whites to 6.8% of Asians to 10.4% for Afro-Caribbeans.

Other factors predicting absent nasal bone in karyotypically normal fetuses included greater crown-rump length (from 4.6% for a CRL of 45-54 mm to 1.0% for CRL 75-84 mm) and nuchal translucency thickness (2% for NT below 2.5 mm to 12% for NT greater than 4.5 mm). The inverse relationship between absent nasal bone and CRL is probably a consequence of the gestational age-dependent rate of bone ossification, Dr. Nicolaides said at the meeting, which was sponsored by the International Society of Ultrasound in Obstetrics and Gynecology.

Because the incidence of absent nasal bone decreases with increasing gestational age, the likelihood of trisomy 21 with an absent nasal bone is greater at 13 weeks than at 11 weeks. Conversely, the incidence of absent nasal bone increases along with NT, so that the likelihood of trisomy 21 with an absent nasal bone is higher with a low NT than a high NT.

Previous data have suggested that a 97% screening sensitivity for trisomy 21 at 11-14 weeks could be achieved with a combination of maternal age, ultrasound scans of NT and the nasal bone, and the maternal serum biochemical markers free [beta]-human chorionic gonadotropin and pregnancy-associated plasma protein. This study, suggesting that the predictive value of the nasal bone depends on ethnic origin, CRL, and NT, was published shortly before the meeting (Ultrasound Obstet. Gynecol. 22[1]:31-35, 2003).

COPYRIGHT 2003 International Medical News Group
COPYRIGHT 2008 Gale, Cengage Learning

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The discovery of a gene involved in memory and learning disabilities in Down’s syndrome means the condition, which is one of the most common genetic abnormalities. may soon be treatable. ‘The bottom line is that we have found one gene that we think is very important.’ says William Mobley. director of a new centre for Down’s syndrome research at Stanford University.

California. The gene causes the neuron damage thought to cause mental retardation. and its discovery means that such retardation could be reversed. ‘From what we have seen in the lab, the neuronal damage is totally …

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The definitive antenatal screening tests for Down’s syndrome are amniocentesis or chorionic villus sampling (CVS). However, as these procedures may in a small number of cases cause spontaneous abortion, it is important that they are only used when the risk of abnormalities in the fetus is high.

A number of indicators can be used in assessing that risk; maternal age is a key determinant along with ultrasound, fetal biometric measurements and three maternal serum factors–alphafetoprotein (AFP), human chorionic gonadotropin (HCG) and unconjugated oestriol (uE3). The relative value of …

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