To determine the recurrence risk for patients with one prior pregnancy affected with neural tube defects (NTD), the authors have pooled data from eight testing centers. In 831 pregnancies studied because one sib was affected with an NTD, the recurrence rate was 3.0%, with 95% confidence limits of 2.0-4.3%, and 99% confidence limits of 1.8-4.8%. The recurrent lesion, whether spina bifida or anencephaly, tended to be concordant with the first to a significant degree. Only 12.2% of recurrent NTD were different from the first, with 95% confidence limits of 4.1-26.2%, and 99% confidence limits of 1.7-30.9%. Both an accurate recurrence risk and the information that a recurrent NTD lesions tends to be concordant with that in the first affected child are useful in the genetic counseling of patients in the United States and in the selection of appropriate prenatal diagnostic studies.
Tetrasomy 9p: confirmation by enzyme analysis SUMMARY A 4-day-old Caucasian male presented with midline defects of the skull and face and extensive skeletal malformations. Chromosome analysis of peripheral blood lymphocytes showed tetrasomy 9p (47,XY, +i(9p)) with no evidence of mosaicism. Confirmation of the cytogenetic interpretation was obtained from the assay of the enzyme galactose-l-P uridyl transferase, the locus for which is on 9p, which showed twice the normal activity.
We have reviewed the results of 10,000 2nd trimester amniocenteses performed at our centre. Over 80 per cent of these were done only because of maternal age (MA); there were three times as many less than 35 year-old women in 1984 compared to 1975. Of women aged 30-34 years at delivery 0.69 per cent were found to have a MA-related chromosome abnormality compared to 0.94 per cent in those aged 35-40 years. Because only about 7 per cent of births occurred to women greater than or equal to 35 years and 18.6 per cent between 30-34 years, and a practical utilization rate of 50 per cent, we recommend that amniocentesis be made available to women aged greater than or equal to 30 years. We believe that 27 per cent of Down syndrome (DS) pregnancies could be identified if 50 per cent of pregnant women in this age category availed themselves of the test. With the same utilization rate, about three times as many amniocenteses would be required in California as performed here in 1983.
Karyotypes of blood and skin fibroblasts at ages 3 and 8.5 years had shown non‐mosaic trisomy 18 in a male now of age 19. Because of his prolonged survival and an atypical phenotype, skin fibroblast cultures from a new biopsy were established at age 18, and only normal 46, XY cells were observed, while peripheral blood lymphocytes still demonstrated 47, XY,+18. This patient and six others with trisomy 18 mosaicism illustrate the advisability of looking for such a pattern in individuals whose phenotype in early life is not fully consistent with the trisomy 18 syndrome. Additional clues to the presence of trisomy 18 mosaicism are male sex, survival beyond 2 years and lack of fingertip arches.
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