Preliminary estimate for the second-trimester maternal serum screening detection rate of the 45,X karyotype using α-fetoprotein, unconjugated estriol and human chorionic gonadotropin

OBJECTIVE

To estimate the detection rate for 45,X pregnancies through second-trimester screening using maternal serum alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol.

METHODS

Twenty-two cases of 45,X were ascertained through a cytogenetics database and an additional 51 cases were identified through publications. Serum analyte concentrations were reviewed for cases with fetal hydrops, cystic hygroma alone, and no evidence of edema. Using the statistical characteristics of this sample of affected pregnancies, computer simulations were carried out to determine the proportion of 45,X pregnancies that should be screen-positive for Down syndrome and trisomy 18. The extent to which additional cases of 45,X might be identified using a protocol specifically designed to detect 45,X pregnancies was also estimated.

RESULTS

Approximately 54% of all 45,X pregnancies should be identifiable through screening for Down syndrome and trisomy 18. The detection rate for cases with hydrops and/or cystic hygroma was 60%, and without edema 33%. If offered with screening for Down syndrome and trisomy 18, 45,X screening could identify approximately 7% more of the affected pregnancies with an incremental rise of 0.2% in the false-positive rate.

CONCLUSIONS

A screening algorithm for 45,X could be developed. However, the number of additional affected pregnancies identified would appear to be too small to justify this screening.

Cost analysis of Down syndrome screening in advanced maternal age

OBJECTIVE

To analyze the potential cost and efficacy of Down syndrome screening in the population with advanced maternal age.

METHODS

Three screening methods defining Down syndrome risk for women with advanced maternal age were analyzed: advanced maternal age; advanced maternal age and maternal serum triple screen; and advanced maternal age, maternal serum triple screen and genetic sonogram. Costs for all tests and procedures were estimated. Procedure-related loss for amniocentesis was assumed to be 1:200. Efficacy was defined as: number of amniocenteses performed, number of Down syndrome cases detected, procedure-related losses, Down syndrome cases detected per fetal loss, cost per Down syndrome case detected and total cost of screening.

RESULTS

In 1999 in the USA, there were 530,610 women with advanced maternal age at 16 weeks' gestation carrying an estimated 4,043 fetuses with Down syndrome. Screening by maternal age alone would result in the 100% detection of Down syndrome cases, but would require over 530,000 amniocenteses and result in 2,653 procedure-related losses. Combining age with serum screen and genetic sonogram would detect 97.6% of Down syndrome cases, but would require only 119,791 amniocenteses and result in 599 procedure-related losses. The projected cost per Down syndrome case detected using age screening is 219,109 dollars versus 155,992 dollars using serum screen and genetic sonogram.

CONCLUSIONS

The combination of advanced maternal age, maternal serum screen and genetic sonogram would result in the fewest procedure-related losses and lowest cost per Down syndrome case detected.

Extreme second-trimester serum analyte values in down syndrome pregnancies with hydrops fetalis

OBJECTIVE

To compare second-trimester maternal serum analyte values in Down syndrome pregnancies with, and without, hydrops fetalis.

METHODS

Seven hydropic and 85 non-hydropic Down syndrome pregnancies were identified among women with positive second-trimester maternal serum screening results. Values for maternal serum alpha-fetoprotein (MSAFP), human chorionic gonadotropin (hCG), unconjugated estriol and inhibin-A, and risks for Down syndrome were compared using the non-parametric Mann-Whitney statistical test.

RESULTS

Hydropic Down syndrome pregnancies had significantly lower MSAFP and estriol concentrations, while hCG levels were higher. For subgroups of five hydropic and 42 non-hydropic cases, no statistically significant difference in the inhibin-A levels could be demonstrated.

CONCLUSION

Second-trimester Down syndrome screening risks are significantly higher in affected pregnancies that are complicated by fetal hydrops.

Role of ultrasound for Down syndrome screening in advanced maternal age

OBJECTIVE

To determine the sensitivity and false-positive rate of Down syndrome screening by use of maternal serum screen and the genetic sonogram in women > or =35 years of age.

STUDY DESIGN

We searched our perinatal databases retrospectively from January 1992 to January 2000 for the following criteria: known Down syndrome fetus or newborn, advanced maternal age, and genetic sonogram from 14-24 weeks' gestation. The a priori maternal age or maternal serum screen risk was modified by likelihood ratios for ultrasound markers. Without markers the risk was reduced by 50%. The cut-off was 1:270.

RESULTS

Age and maternal serum screen had a sensitivity of 90.5% and a false-positive rate of 27.1%. Age and ultrasound had a 95.2% sensitivity and 43.5% false-positive rate, whereas the combination of age, maternal serum screen, and ultrasound had a 97.6% sensitivity and a 22.0% false-positive rate.

CONCLUSION

The combination of age, maternal serum screen, and ultrasound improves the sensitivity for Down syndrome detection in the advanced maternal age population.

Second trimester maternal serum analytes in triploid pregnancies: correlation with phenotype and sex chromosome complement

Second trimester maternal serum alpha-fetoprotein (MS-AFP), human chorionic gonadotrophin (hCG), unconjugated estiol (uE3), and inhibin-A (INH-A) levels were evaluated in pregnancies complicated by triploidy. In addition to seven new triploid pregnancies, the results for 67 published cases were reviewed. All cases appear to fall into two major groups. First, those identifiable as screen-positive for both Down syndrome and an open neural tube defect (ONTD) with elevated MS-AFP, grossly elevated hCG, low/normal uE3, and probably elevated INH-A. Pregnancies in the second group are identifiable as screen-positive for trisomy 18 with low/normal MS-AFP, and very low hCG, uE3 and INH-A. Triploid pregnancies with high maternal serum hCG nearly always show a placenta with partial mole (25/27 or 93%), a high frequency of ONTDs or ventral wall defects (VWDs) (8/28 or 29%) and have either an XXX or XXY karyotype (observed ratio 6:10, respectively). Low hCG is infrequently associated with a molar placenta (1/11 or 9%), does not appear to be associated with ONTDs or VWDs (0/29 or 0%), and shows an excess of XXX over XXY karyotypes (observed ratio 17:2). There were 16 cases with either a molar placenta, an ONTD or a VWD that received the MS-AFP and hCG tests. All 16 were screen-positive for an ONTD (MS-AFP> or =2 multiples of the median). In addition, all 31 cases that received MS-AFP, hCG, uE3 (and where available INH-A) were screen-positive for either Down syndrome or trisomy 18. The findings are discussed in the context of expected differences between digynic and diandric triploidy. It is suggested that the sex chromosome complement in triploidy is an important factor in determining risk for partial mole development and in utero survival.

Estimates for the sensitivity and false-positive rates for second trimester serum screening for Down syndrome and trisomy 18 with adjustment for cross-identification and double-positive results

Second trimester screening for fetal Down syndrome and trisomy 18 is available through separate protocols that combine the maternal age-specific risk and the analysis of maternal serum markers. We have determined the extent to which additional Down syndrome affected pregnancies may be identified through trisomy 18 screening, and the extent to which additional cases of trisomy 18 may be screen-positive for Down syndrome. The combined false-positive rate, taking into consideration those pregnancies that are screen-positive by both protocols, has also been determined. Sensitivity and false-positive rates were determined by computer simulation of results that incorporated previously published statistical variables into the model. Using second trimester risk cut-offs of 1:270 for Down syndrome and 1:100 for trisomy 18, it was found that few additional cases of Down syndrome are identified through trisomy 18 screening. However, approximately 6-10% of trisomy 18 affected pregnancies will be screen-positive for Down syndrome but screen-negative for trisomy 18. For women aged 40 or more, the false-positive rate for trisomy 18 exceeds 1% and approximately half of these cases will also be screen-positive for Down syndrome. For a population with maternal ages equivalent to that in the United States in 1998, after adjusting for the cross-identification, the sensitivity for three-analyte trisomy 18 screening is 78%. If this testing is performed in conjunction with Down syndrome "triple" screening, the Down syndrome sensitivity is 75% and the combined false-positive rate is 8.5%. If the three-analyte trisomy 18 screening is performed with the Down syndrome "quad" screen, the trisomy 18 sensitivity remains at 78%, the Down syndrome sensitivity is 79%, and combined false-positive rate is 7.5%. Sensitivity and false-positive rates are also provided for other widely used Down syndrome and trisomy 18 risk cut-offs. Sensitivity and false-positive rates that take into consideration cross-identification and double-positives should be helpful for pre-test counseling and the evaluation of serum screening programs.

Evaluation of effect of analytical imprecision in maternal serum screening for Down's syndrome

Formulae to evaluate the effect of inter-assay analytical imprecision (expressed as the coefficient of variation) in maternal serum screening for Down's syndrome have been developed. Experimentally determined imprecision in Down's syndrome risk (based on maternal serum alpha-fetoprotein, unconjugated oestriol and human chorionic gonadotrophin) was found to be consistent with predicted values. Imprecision in the measurement of analytes becomes amplified when risk is calculated using the values of these analytes. A large separation between the means and small standard deviations for normal and affected pregnancies are the characteristics of the tests most useful in screening, but these attributes also result in the most imprecision in risk. In addition, the relative imprecision associated with Down's syndrome risk is not the same for all women screened. Combining tests for multivariate analyses results in a complex compounding of the errors. The need for strict quality control and test reproducibility is emphasized. The effect of analytical imprecision should be of particular concern to laboratories that provide screening for women of advanced maternal age.

Elevated maternal serum alpha-fetoprotein with low unconjugated estriol and the risk for lethal perinatal outcome

OBJECTIVE

To determine whether a combination of elevated maternal serum alpha-fetoprotein (MSAFP) and low unconjugated estriol (E3) concentration identifies pregnancies at particularly high risk for fetal abnormality or poor outcome.

METHODS

Pregnancy outcomes were reviewed for women with elevated MSAFP (> or =2.0 MoM) from our database of 50,315 women who had received triple marker testing from 1993-1998. Outcomes for those with low E3 (< or =0.7 MoM) were compared with those with normal E3 (>0.7 MoM). The incidences of fetal death, neural tube defects, chromosome abnormalities, congenital abnormalities, preterm birth, small-for-gestational age (SGA), twins, and inaccurate dates were compared in the two groups using Fisher's exact test with P < 0.05 considered significant.

RESULTS

Of the 50,315 women screened, 1,435 (2.85%) had an elevated MSAFP. Pregnancy outcomes were obtained in 94% of those with elevated MSAFP and 70% of all patients screened. Neural tube defects were present in 57 fetuses/infants (21 anencephalic, 29 spina bifida, 7 encephalocele) of which 46 (81%) had an elevated MSAFP. Of the 1,435 women with an elevated MSAFP, 199 (14%) had a low E3. Compared to those women with elevated MSAFP but normal E3, women with elevated MSAFP and low E3 were at significantly increased risk for fetal death (20.6% vs. 2.8%, relative risk (RR) 8.9), anencephaly (9.0% vs. 0.1%, RR 122.8) and chromosome abnormality (2.5% vs. 0.6%, RR 4.0).

CONCLUSIONS

Pregnancies complicated by elevated second trimester MSAFP and low E3 are at a particularly high risk (32%) for lethal perinatal outcomes. Twins, while a common cause of elevated MSAFP, are rarely found when an elevated MSAFP is associated with low E3.

Unexplained elevated midtrimester maternal serum levels of alpha fetoprotein, human chorionic gonadotropin, or low unconjugated estriol: recurrence risk and association with adverse perinatal outcome

OBJECTIVE

To determine if women experiencing an unexplained elevated maternal serum alpha fetoprotein (MSAFP; > or =2.0 MoM) or human chorionic gonadotropin (hCG; > or =2.0 MoM), or low unconjugated estriol (E3; < or =0.5 MoM) in one pregnancy are at increased risk for similar results in a subsequent pregnancy, and to determine if recurrence of these analyte extremes is associated with adverse perinatal outcome.

METHODS

We identified all women delivering two consecutive singleton pregnancies at one hospital between 1992-1997 for whom second trimester trisomy 21 serum screen was performed in each pregnancy. All screens were performed in a single laboratory. Each pregnancy delivered after 20 weeks and had gestational age confirmed by ultrasound prior to 24 weeks. Subjects were excluded if a fetal anomaly or aneuploidy was present. Adverse outcomes included abruption, oligohydramnios, preeclampsia, preterm membrane rupture, preterm delivery, stillbirth, birthweight <10th centile, and admission to neonatal intensive care unit (NICU).

RESULTS

A total of 538 women had 1,076 pregnancies meeting inclusion criteria; 12/515 (2.3%) of women with a normal MSAFP, 28/470 (6.0%) with a normal hCG, and 11/504 (2.2%) with a normal E3 in the first pregnancy had an anomalous result for the respective analyte in the second pregnancy. In contrast, only 4/23 (17.4%) patients with an elevated MSAFP (P = 0.003), 14/44 (31.8%) with an elevated hCG (P < 0.001), and 2/10 (20.0%) with a low E3 (P < 0.025) in the first pregnancy had the same analyte anomaly recur in the second pregnancy. The odds ratios for recurrent elevated MSAFP, hCG, and low E3 were 7.5, 5.3, and 9.2, respectively. Adverse perinatal outcomes occurred with similar frequency, regardless of MSAFP, hCG, or E3 results in consecutive pregnancies, using women with normal MSAFP, hCG, and E3 results in one or both pregnancies as controls.

CONCLUSIONS

Women experiencing an anomalous serum analyte in one pregnancy are at significant risk to experience the same analyte result in a subsequent pregnancy.

Predictive value of the triple screening test for the phenotype of Down syndrome

Maternal serum alpha-fetoprotein (MSAFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3) are routinely measured in the second trimester ("triple" test) and combined with maternal age to evaluate risk for fetal Down syndrome. Triple test results and clinical findings were retrospectively reviewed for 30 newborns with Down syndrome to determine whether analyte values or second trimester risks for Down syndrome were more extreme in affected pregnancies where cardiac or other severe congenital malformations were present compared to those cases where major anatomical abnormalities were absent. Mean MS-AFP, uE3, maternal age, and second trimester Down syndrome risk were all similar in the two groups of pregnancies. However, hCG concentrations did appear to be higher in the group of Down syndrome pregnancies with anatomical anomalies (mean 1.74 MoM versus 1.19 MoM) (P<0.05). Overall, there was no significant difference in the incidence of major anomalies in patients with screen-positive test results versus those cases that were not identified by the triple test. Prenatal counseling should therefore reflect the general expectations of the Down syndrome phenotype that have been established from live-born infants with this disorder.

Cost-effectiveness of estimating gestational age by ultrasonography in Down syndrome screening

OBJECTIVE

To quantify the financial benefits of using ultrasound estimation of gestational age in maternal serum screening for Down syndrome.

METHODS

Maternal age-specific sensitivity and false-positive rates for Down syndrome were derived for the triple test (alpha-fetoprotein, hCG, and unconjugated estriol) using gestational age based on ultrasound dating and also time from the last menstrual period (LMP). These rates were entered into a formula to determine the societal financial net benefit of Down syndrome screening. The average per-case net benefits of ultrasound- and LMP-dated pregnancies were then compared. Average net benefits were also calculated separately with ultrasound versus LMP dating for triple tests referred to our laboratory, and the additional costs associated with any post-test ultrasound scans, repeat testing, or recalculations were estimated.

RESULTS

The use of ultrasound dating resulted in higher detection rates for Down syndrome and lower false-positive rates, which translated into an average per-case savings to society of $33.54. For women referred to our program with LMP dating, there was an average reduction of $31.60 in net benefits, plus added costs of $14.39 attributable to extra ultrasound, repeat testing, and recalculation.

CONCLUSION

When ultrasound dating is available before serum screening, it should be used preferentially to establish Down syndrome risk. Routine first-trimester ultrasound examination can be justified for women with a known LMP if the cost of the ultrasound examination is less than $46.

Maternal serum screening for fetal trisomy 18: a comparison of fixed cutoff and patient-specific risk protocols

OBJECTIVE

To compare the effectiveness of two widely used protocols for second-trimester screening for fetal trisomy 18.

METHODS

Second-trimester screening results for 41,565 women were reviewed to determine whether pregnancies could be considered to be at high risk for trisomy 18. The screening test was considered positive if either maternal serum concentrations of alpha-fetoprotein (MSAFP), hCG, and unconjugated estriol (E3) fell below defined levels, or the second-trimester patient-specific risk (based on maternal age and serum analytes) was greater than 1:100. Detection rates, false-positive rates, and pregnancy outcomes for the two protocols were compared.

RESULTS

The fixed-cutoff method showed a 23% detection rate and a 0.19% false-positive rate for trisomy 18. These low rates were in close agreement with a theoretical expectation for fixed-cutoff trisomy 18 screening. The risk-based approach resulted in a 69% detection rate and a 0.45% false-positive rate. Both methods identified pregnancies with other fetal anomalies.

CONCLUSION

Overall, the risk-based method is more effective than the fixed-cutoff approach to trisomy 18 screening.

X-chromosome abnormalities in women with premature ovarian failure

OBJECTIVE

To evaluate the significance of X-chromosome abnormalities identified in a series of women with premature ovarian failure (POF).

STUDY DESIGN

Karyotypes were reviewed for all women referred to our cytogenetic laboratory over a five-year interval with the diagnosis of POF. Thirty women aged less than 40 with unexplained secondary amenorrhea and elevated follicle-stimulating hormone were included.

RESULTS

Of the 30 patients, 26 had a normal karyotype and 4 showed the following X-chromosome abnormalities: 46,Xi(Xq), 45,X/46,XX mosaic, 46,X,der(X)t(X;Y)(q28;q12) mat and 46,X,t(X;5)(q22;q11.2) mat. In the two families with familial translocations, carrier females within each family showed considerable variability in age at onset of menopause.

CONCLUSION

Both familial and nonfamilial X-chromosome abnormalities can be identified in women with POF. Cytogenetic studies should not be limited to those patients with very-early-onset POF.

45,X/46,XX mosaicism in patients with idiopathic premature ovarian failure

OBJECTIVE

To determine whether low-level 45,X/46,XX mosaicism may be present in some women with premature ovarian failure (POF).

DESIGN

Slide preparations were made from lymphocyte cultures stimulated with phytohemagglutinin, and fluorescence in situ hybridization (FISH) was then performed using a biotin-labeled X-chromosome probe.

SETTING

Cytogenetics laboratory.

PATIENT(S)

Fifteen women with idiopathic POF, 20 age-matched controls, and an additional 10 older control women with normal reproductive histories.

INTERVENTION(S)

Blood samples were collected.

MAIN OUTCOME MEASURE(S)

The number of X chromosomes present in each cell.

RESULT(S)

In patients with POF, the percentage of cells with a single X chromosome (mean, 5.50) was significantly greater than in the controls of similar age (mean, 2.42). For control subjects, there appeared to be a linear correlation between the number of cells with a single X chromosome and age.

CONCLUSION(S)

Some cases of POF may be attributable to low-level 45,X/46,XX mosaicism, which can be detected using FISH. In the lymphocytes from normal women, the rate of accumulation of cells with a single X chromosome was approximately 700 per 10(6) cells per year.

Preliminary evidence for associations between second-trimester human chorionic gonadotropin and unconjugated oestriol levels with pregnancy outcome in Down syndrome pregnancies

Fifty-six cases of Down syndrome were identified in a population of women who had undergone maternal serum triple marker screening [alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated oestriol (uE3) analyses]. These affected pregnancies represented all known cases present in the population of 34,368 women screened. Using a 1:270 mid-trimester Down syndrome risk to define the screen-positive group, 42 affected pregnancies were screen-positive (medians: AFP = 0.79 MOM, hCG = 2.13 MOM, uE3 = 0.62 MOM, age 34.6 years) and 14 pregnancies were screen-negative (medians: AFP = 0.82 MOM, hCG = 1.57 MOM, uE3 = 0.92 MOM, age 24.2 years). Four affected pregnancies were associated with in utero death and each of these cases was associated with relatively extreme values of AFP, hCG, and uE3, including the three highest levels of hCG in the entire series of Down syndrome pregnancies. Twenty-nine (15 screen-positive and 14 screen-negative) affected pregnancies resulted in liveborns. Down syndrome pregnancies had a significantly shorter gestational term than controls, and Down syndrome babies were also lighter than controls, even after adjustment for sex and gestational age. In affected pregnancies, a low uE3 level appeared to be associated with a greater chance of a small-for-gestational age baby. No correlations could be demonstrated between AFP or hCG levels and gestational age-adjusted term weight. Based on this small series, it would appear that uE3 may be particularly useful in detecting those Down syndrome cases associated with small-for-gestational age fetuses. A very high hCG value may indicate a higher probability of fetal death.

Down syndrome and neural tube defect screening: the value of using gestational age by ultrasonography

OBJECTIVE

Our goal was to determine whether gestational age should be based on ultrasonographic evaluation or last menstrual period data in the interpretation of second-trimester maternal serum screening for Down syndrome and open neural tube defects.

STUDY DESIGN

Initial and revised screen-positive rates and detection rates were reviewed for women undergoing triple-marker testing (maternal serum alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol). The study population consisted of > 24,000 women at 15.0 to 21.9 weeks' gestation with approximately 60% of test interpretations based on ultrasonographic evaluation of gestational age. Gestational age and screening results were compared for 24 Down syndrome pregnancies in which both ultrasonography and last menstrual period dating were available.

RESULTS

Both initial and revised screen-positive rates for Down syndrome were significantly lower when ultrasonographic data were used compared with last menstrual period dating. The detection rate for Down syndrome appeared to be higher with ultrasonographic dating (approximately 76% vs 60% for last menstrual period dating). Down syndrome fetuses had a significantly shorter gestational age when evaluated by ultrasonography (relative to last menstrual period dating), but a similar trend was also seen in control pregnancies. Initial and revised screen-positive rates for open neural tube defects were higher for women who had received an ultrasonographic examination compared with the rates for those women referred with only last menstrual period data. The detection rates for open neural tube defects were similar for both methods of pregnancy dating.

CONCLUSION

By use of ultrasonographic measurement of gestational age, the number of amniocenteses performed to detect Down syndrome can be substantially reduced while detection rates are maintained or improved.

Angelman syndrome associated with an inversion of chromosome 15q11.2q24.3

Angelman syndrome (AS) most frequently results from large (> or = 5 Mb) de novo deletions of chromosome 15q11-q13. The deletions are exclusively of maternal origin, and a few cases of paternal uniparental disomy of chromosome 15 have been reported. The latter finding indicates that AS is caused by the absence of a maternal contribution to the imprinted 15q11-q13 region. Failure to inherit a paternal 15q11-q13 contribution results in the clinically distinct disorder of Prader-Willi syndrome. Cases of AS resulting from translocations or pericentric inversions have been observed to be associated with deletions, and there have been no confirmed reports of balanced rearrangements in AS. We report the first such case involving a paracentric inversion with a breakpoint located approximately 25 kb proximal to the reference marker D15S10. This inversion has been inherited from a phenotypically normal mother. No deletion is evident by molecular analysis in this case, by use of cloned fragments mapped to within approximately 1 kb of the inversion breakpoint. Several hypotheses are discussed to explain the relationship between the inversion and the AS phenotype.

Rare trisomy mosaicism diagnosed in amniocytes, involving an autosome other than chromosomes 13, 18, 20, and 21: karyotype/phenotype correlations

In order to determine the significance of trisomy mosaicism of an autosome other than chromosomes 13, 18, 20, and 21, 151 such cases diagnosed prenatally through amniocentesis were reviewed. These rare trisomy mosaicism cases include 54 from 17 cytogenetic laboratories, 34 from a previous North American mosaicism survey, and 63 from published reports. All were cases of true mosaicism with information available on pregnancy outcome, and with no evidence of biased ascertainment. There were 11 cases of 46/47, +2; 2 of 46/47, +3; 2 of 46/47, +4; 5 of 46/47, +5; 3 of 46/47, +6; 8 of 46/47, +7; 14 of 46/47, +8; 25 of 46/47, +9; 2 of 46/47, +11; 23 of 46/47, +12; 5 of 46/47, +14; 11 of 46/47, +15; 21 of 46/47, +16; 7 of 46/47, +17; 1 of 46/47, +19; and 11 of 46/47, +22. As to the risk of an abnormal outcome, the data showed a very high risk (> 60 per cent) for 46/47, +2, 46/47, +16, and 46/47, +22; a high risk (40-59 per cent) for 46/47, +5, 46/47, +9, 46/47, +14, and 46/47, +15; a moderately high risk (20-39 per cent) for 46/47, +12; a moderate risk (up to 19 per cent) for 46/47, +7 and 46/47, +7 and 46/47, +8; a low risk for 46/47, +17; and an undetermined risk, due to lack of cases, for the remaining autosomal trisomy mosaics. Most cases were evaluated at birth or at termination, so subtle abnormalities may have escaped detection and developmental retardation was not evaluated at all. Comparison of the phenotypes of prenatally diagnosed abnormal cases and postnatally diagnosed cases with the same diagnosis showed considerable concordance. Since the majority of anomalies noted are prenatally detectable with ultrasound, an ultrasound examination should be performed in all prenatally diagnosed cases. In cytogenetic confirmation studies, the data showed much higher confirmation rates in cases with abnormal outcomes than in cases with normal outcomes [81 per cent vs. 55 per cent for fibroblasts (from skin, fetal tissue, and/or cord); 88 per cent vs. 46 per cent for placental cells; 22 per cent vs. 10 per cent for blood cells]. The confirmation rate reached 85 per cent when both fibroblasts and placental tissues were studied in the same case (with trisomic cells found in one or the other, or both). Therefore, one must emphasize that both fibroblasts and placental tissues should be studied. Except for 46/47, +8 and 46/47, +9, PUBS is of limited value for prenatal diagnosis of rate trisomy mosaicism. DNA studies for UPD are suggested for certain chromosomes with established imprinting effects, such as chromosomes 7, 11, 14, and 15, and perhaps for chromosomes 2 and 16, where imprinting effects are likely.

Medians for second-trimester maternal serum alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol; differences between races or ethnic groups

Second-trimester maternal serum alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3) are routinely measured in screening fetuses at high risk for Down syndrome or open neural tube defects (ONTD). For test interpretation, individual patient values of these three analytes are related to population-derived median values. We evaluated data from >21000 pregnancies to determine the extent of race-specific differences in median concentrations. For samples at most gestational ages, median AFP, hCG, and uE3 values for white, black, Hispanic, and other patients were all significantly different. Differences remained significant even when data were corrected for patient weights. For each analyte, the extent of the variation was not the same at different gestational ages. Differences in median values across race/ethnicity groups appear to have only a small impact in Down syndrome screening but it may be appropriate to use alternative sets of AFP medians or adjustment factors to AFP medians for some Asian populations receiving ONTD screening.

Maternal serum screening for birth defects: results of a Connecticut regional program

Second trimester maternal serum screening provides a method to identify pregnancies at high risk for fetal Down's syndrome, trisomy 18, open neural tube defects, and a variety of other chromosomal and nonchromosomal fetal anomalies. Results are presented for a regional program to identify high-risk pregnancies using alpha feto-protein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3) analyses (triple marker testing). A total of 27,140 women received screening. Using a midtrimester Down's syndrome risk of 1:270 to define the high-risk group, 5.26% of women of all ages were screen-positive for Down's syndrome resulting in the eventual detection of approximately 72% of the affected fetuses. The detection rate for patients under 35 at estimated date of delivery was 61% and for women 35, or older, the detection rate was 100%. A separate protocol to screen for trisomy 18 identified 0.2% of pregnancies, with 38% of the trisomy 18 cases present in this group. Over 3% of women screen-positive for Down's syndrome or trisomy 18 had a serious fetal chromosome anomaly. In addition, 2.89% of women had an elevated AFP (greater or equal to 2.0 multiples of median). This component of the screening resulted in the identification of 86% of the neural tube defects, 75% of the ventral wall defects, and also some of the other various fetal anomalies present in the screened population. Since both laboratory and clinical data are combined to generate patient-specific risks, there is a need for quality control elements that go beyond that normally required for a clinical laboratory alone. We stress the need for comprehensive follow-up programs to evaluate screening programs and maintain high quality.

Elevated second-trimester maternal serum hCG alone or in combination with elevated alpha-fetoprotein

OBJECTIVE

To evaluate the clinical significance of a second-trimester elevated maternal serum hCG in women carrying singleton, chromosomally normal fetuses.

METHODS

The results of second-trimester maternal serum screening (alpha-fetoprotein [MSAFP], hCG, and unconjugated estriol) for 25,438 women were reviewed, and those with hCG values exceeding 3.0 multiples of the median (MoM) were identified. A control population was selected only on the basis of samples accessioned by the laboratory at the same time as the study group. Follow-up information was collected from physicians' offices for both groups. Incidence of fetal or neonatal loss (spontaneous abortion, fetal death, and neonatal death combined), preterm birth (before 37 weeks' gestation), small for gestational age, and preeclampsia were compared.

RESULTS

Three hundred twenty-two women (1.3%) had hCG levels exceeding 3.0 MoM. In addition to chromosomal abnormalities and fetal death at the time of testing, this group showed a significantly higher incidence of fetal or neonatal death, preterm birth, low birth weight, and preeclampsia than did controls. For patients with elevated second-trimester hCG, many of the preterm deliveries occurred before 34 weeks' gestation. Logistic regression analysis indicated that hCG, MSAFP, and race were significant independent factors in predicting risk for adverse outcome.

CONCLUSIONS

Similar to elevated AFP, elevated hCG is associated with poor pregnancy outcome. By combining the results of the two tests, it may be possible to improve substantially the identification of patients at very high risk for adverse outcomes.

Prenatal diagnosis of diverse chromosome abnormalities in a population of patients identified by triple-marker testing as screen positive for Down syndrome

OBJECTIVE

Our purpose was to determine the incidence of all types of chromosome abnormalities (i.e., trisomy 21 and other abnormalities) in women receiving prenatal chromosome analysis after a Down syndrome screen-positive result by maternal serum triple-marker testing (alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol analyses).

STUDY DESIGN

A total of 11,434 patients between 15.0 and 21.9 weeks' gestation received second-trimester Down syndrome risk evaluation by triple-marker testing. By use of a 1:270 midtrimester Down syndrome risk cutoff value, and after ultrasonographic confirmation of gestational age, 677 patients were screen positive for Down syndrome (corrected screen-positive rate 5.92%). Karyotypes were reviewed for 468 (69%) of these patients who received prenatal chromosome analysis.

RESULTS

In addition to 12 cases of Down syndrome, 12 other fetal chromosome abnormalities were found (i.e., 5.13% had a chromosome abnormality of some type). Expressed as a proportion of all patients with a corrected Down syndrome screen-positive result, at least 3.69% had a chromosome abnormality. The overall spectrum of abnormal karyotypes (approximately 50% autosomal trisomy, 25% structural and 25% sex chromosome abnormality) appears to be comparable to that seen in patients undergoing amniocentesis because of advanced maternal age.

CONCLUSIONS

As is the case for women of advanced maternal age, preamniocentesis counseling for patients with positive triple-marker testing results should reflect the relatively high probability that an abnormality other than Down syndrome may be identified.

Comparison of high resolution chromosome banding and fluorescence in situ hybridization (FISH) for the laboratory evaluation of Prader-Willi syndrome and Angelman syndrome

The development of probes containing segments of DNA from chromosome region 15q11-q13 provides the opportunity to confirm the diagnosis of Prader-Willi syndrome (PWS) and Angelman syndrome (AS) by fluorescence in situ hybridization (FISH). We have evaluated FISH studies and high resolution chromosome banding studies in 14 patients referred to confirm or rule out PWS and five patients referred to confirm or rule out AS. In four patients (three from the PWS category and 1 from the AS group) chromosome analysis suggested that a deletion was present but FISH failed to confirm the finding. In one AS group patient, FISH identified a deletion not detectable by high resolution banding. Review of the clinical findings in the discrepant cases suggested that the FISH results were correct and high resolution findings were erroneous. Studies with a chromosome 15 alpha satellite probe (D15Z) on both normal and abnormal individuals suggested that incorrect interpretation of chromosome banding may occasionally be attributable to alpha satellite polymorphism but other variation of 15q11-q13 chromosome bands also contributes to misinterpretation. We conclude that patients who have been reported to have a cytogenetic deletion of 15q11-q13 and who have clinical findings inconsistent with PWS and AS should be re-evaluated by molecular genetic techniques.

Review of the cytogenetic changes in acute megakaryoblastic leukemia: one disease or several?

The karyotypes of 116 cases of acute megakaryoblastic leukemia (AMKL) were reviewed, including 43 pediatric patients with Down syndrome (DS) and 73 non-DS patients. DS patients with AMKL often had a history of transient leukemia or myelodysplasia with an early age of onset of AMKL (median 23 months). In these patients, the frequency of additional cytogenetic change (numerical or structural) was low, with 10 of the 43 DS patients showing no additional cytogenetic change. A second group of patients had t(1;22)(p13;q13) or other cytogenetic abnormality involving 22q13. These patients had no history of transient leukemia but showed very early onset of AMKL. In this group of patients, marked organomegaly was noted; these patients also showed few specific additional cytogenetic changes. The remaining AMKL patients had a median age of 30 years with much more frequent cytogenetic changes, including rearrangement of 3q21 and 3q26-27, trisomy 21, and other specific changes. Based on the karyotype and clinical data, we hypothesize that AMKL may represent at least three separate disease entities with different genetic alterations giving rise to similar, but not identical, disorders. Subclassification of AMKL on the basis of the cytogenetic changes in the leukemic cells appears to be justified.

Altered epidermal growth factor signal transduction in activated Ha-ras-transformed human keratinocytes

Epidermal growth factor (EGF) can stimulate proliferation and 92 kDa gelatinase/matrix metalloproteinase (MMP-9) expression. The induction of MMP-9 is not only pathologically significant for invasion and metastasis, but also serves as a semiquantitative measure of EGF signal transduction. In order to examine the role of mutated ras p21 in EGF signal transduction, an activated Ha-ras-transformed human keratinocyte cell line was developed and characterized. Overexpression of the mutated Ha-ras p21 in these cells was demonstrated. Our results showed that EGF induced 92 kDa MMP-9 secretion was doubled in the ras-transformed keratinocytes in comparison to the parent cells. The karyotype, the expression of EGF receptor (EGFR) and transforming growth factor (TGF) alpha at the mRNA level remained unchanged. These results suggest that the presence of high levels of mutated ras p21 may be responsible for the aberrant EGF signal transduction and contributes to transformation. In addition, a reduction of TGF beta expression at mRNA level by 70% was found in the activated Ha-ras-transformed keratinocytes when compared to the parent cells.

Proposed guidelines for diagnosis of chromosome mosaicism in amniocytes based on data derived from chromosome mosaicism and pseudomosaicism studies

Currently, accepted protocol which has been developed at the Prenatal Diagnosis Laboratory of New York City (PDL) requires that when a chromosome abnormality is found in one or more cells in one flask, another 20-40 cells must be examined from one or two additional flasks. Chromosome mosaicism is diagnosed only when an identical abnormality is detected in cells from two or more flasks. In a recent PDL series of 12,000 cases studied according to this protocol, we diagnosed 801 cases (6.68 per cent) of single-cell pseudomosaicism (SCPM), 126 cases (1.05 per cent) of multiple-cell pseudomosaicism (MCPM), and 24 cases (0.2 per cent) of true mosaicism. Pseudomosaicism (PM) involving a structural abnormality was a frequent finding (2/3 of SCPM and 3/5 of MCPM), with an unbalanced structural abnormality in 55 per cent of SCPM and 24 per cent of MCPM. We also reviewed all true mosaic cases (a total of 50) diagnosed in the first 22,000 PDL cases. Of these 50 cases, 23 were sex chromosome mosaics and 27 had autosomal mosaicism; 48 cases had numerical abnormalities and two had structural abnormalities. Twenty-five cases of mosaicism were diagnosed in the first 20 cells from two flasks, i.e., without additional work-up, whereas the other 25 cases required extensive work-up to establish a diagnosis (12 needed additional cell counts from the initial two culture flasks; 13 required harvesting a third flask for cell analysis). Our data plus review of other available data led us to conclude that rigorous efforts to diagnose true mosaicism have little impact in many instances, and therefore are not cost-effective. On the basis of all available data, a work-up for potential mosaicism involving a sex chromosome aneuploidy or structural abnormality should have less priority than a work-up for a common viable autosomal trisomy. We recommend revised guidelines for dealing with (1) a numerical versus a structural abnormality and (2) an autosomal versus a sex chromosome numerical aneuploidy. Emphasis should be placed on autosomes known to be associated with phenotypic abnormalities. These new guidelines, which cover both flask and in situ methods, should result in more effective prenatal cytogenetic diagnosis and reduced patient anxiety.

Densitometric analysis of Southern blot autoradiographs and its application to monitoring patients with chronic myeloid leukemia

The characteristic genetic exchange in chronic myeloid leukemia (CML) is the fusion of the ABL proto-oncogene and a specific part of the BCR or phl gene. Detection of this exchange by cytogenetic or Southern blot analysis is highly diagnostic for CML. The latter approach has not previously been used to quantify the relative proportions of leukemic and non-leukemic cells. We have assessed the feasibility of estimating the relative proportion of leukemic cells present in a sample by densitometric analysis of autoradiographs of Southern blots. In dilution experiments of CML cells with normal cells, a linear relationship could be demonstrated between the relative intensity of the autoradiograph band corresponding bcr rearrangement and the proportion of leukemic cells present. This relationship was found to be largely independent of autoradiograph exposure time. Six patients receiving various therapies have been evaluated for as long as 4.5 years by repeated densitometric and cytogenetic analysis. In general, a declining proportion of Philadelphia (Ph) chromosome positive cells was paralleled by decreasing intensity of the autoradiograph band representing bcr rearrangement. Densitometric changes were often seen prior to the detection of Ph negative cells. This analysis appears to provide a sensitive method for monitoring patients with CML.

Fine mapping of chromosome 22 breakpoints within the breakpoint cluster region (bcr) implies a role for bcr exon 3 in determining disease duration in chronic myeloid leukemia

The chromosomal translocation that fuses the phl gene with the c-abl proto-oncogene appears to be a pivotal step in the pathogenesis of some leukemias. In chronic myeloid leukemia (CML) the breakage within the phl gene is largely confined to a 5.8-kb segment referred to as the breakpoint cluster region (bcr). To determine whether the presence of specific bcr exons on the Philadelphia chromosome has any clinical significance, we have analyzed the bcr breakpoints in 134 patients with CML. As many as five probes were used in this analysis, including a synthetic oligonucleotide probe homologous to the bcr exon 3 (phl exon 14) region. The distribution of breakpoints indicates that, in fact, breakage is largely confined to a 3.1-kb segment lying between bcr exon 2 and exon 4 (phl exons 13-15). In 61 CML patients analyzed within 1 year of diagnosis, the distribution of breakpoints appeared to be random within the 3.1-kb region. However, a significant excess of 5' breakpoints was observed in the total population studied, consistent with previous data showing that patients with 3' breakpoints have shorter disease durations. Analysis using the bcr exon 3 sequence probe indicated it was probably the presence or absence of bcr exon 3 on the Philadelphia chromosome that accounts for some of the variability in disease duration seen in CML. The data suggest that the phl/abl protein product may influence the timing of the onset of blast crisis and imply a continuing role for this protein during the evolution of the disease.

Prenatal diagnosis of minute 5p- deletion: a cytogenetic problem in detection

An unbalanced translocation, 46,XX,der(5)t(5;11) (p15;q25)mat was ascertained by prenatal diagnosis. The mother previously had a liveborn child with cri du chat syndrome. The subtlety of the chromosome rearrangement in this case illustrates the need for the most detailed cytogenetic investigations in cri du chat cases when deletion or translocation are not immediately obvious.

Chromosomal polymorphisms of 1, 9, 16, and Y in 4 major ethnic groups: a large prenatal study

Using trypsin Giemsa banding (GTG), major polymorphisms of the constitutive heterochromatin regions of chromosome 1, 9, 16, and Y were recorded in a New York City population. Polymorphisms were recorded from amniotic fluid specimens received from 6,250 patients from 4 major population groups, ie, White (European)-2,334 cases, American Black-1,795 cases, Hispanic descent-1,737 cases, and Asian (Oriental and Indian)-384 cases. The major chromosomal polymorphisms were classified as follows: obvious pericentric inversion of the constitutive heterochromatin of the long arm of the chromosome (inv qh); significantly enlarged heterochromatic region of the long arm (qh + is greater than, or equal to, twice the size of the short arm of chromosome 16 [16p]); very small or deficient heterochromatic region in the long arm (qh-); large Y (Yq + greater than size of chromosome 18), small Y (Yq- less than size of a G-group chromosome), and pericentric inversion of Y. Our prenatal study confirmed that the incidence of specific chromosomal variants is different in each population group. The most striking examples of this are the pericentric inversion of chromosome 9 and the different polymorphisms of the Y chromosome. The incidence of inv (9) is highest in the Black population (3.57%); slightly above average in Hispanics (2.42%); and relatively low in Whites (0.73%) and Asians (0.26%). The Y appears to be more variable in Asian (3.37%) and Hispanic (1.82%) than in White or Black groups. The 9qh+ is seen more frequently than 1qh+, or 16qh+. Inv (1), 9qh-, and 16qh- are rare. There were no cases of either 1qh- or inv (16).(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for preferential involvement of chromosome bands 6p21 and 13q14 in amniotic fluid cell balanced translocation pseudomosaicism

Chromosome rearrangement is a relatively common finding in cultured amniotic fluid cells. When cytogenetic abnormalities are confined to one cell or cells from a single culture, they are generally assumed to have arisen in culture (pseudomosaicism). To determine whether or not there might be some specificity in chromosome break-points in balanced translocation multiple cell pseudomosaicism, data has been pooled for 18 cases studied at PDL and 30 cases from the U.S. survey on mosaicism and pseudomosaicism (Hsu & Perlis 1984). Out of a total of 97 break-points, 87 were assigned to Giemsa-staining light bands and 12 to Giemsa-staining dark bands. An excess of break points (29%) were assigned to terminal bands. Two loci appeared to be preferentially involved in rearrangement: six break-points (4 PDL cases and 2 others) were assigned to band 6p21; the region to which the major histocompatibility complex (HLA) has been assigned; Four break-points (all PDL cases) were assigned to 13q14, the region associated with the retinoblastoma locus. This preliminary evidence for specific break-points needs confirmation and long-term follow-up information is needed to determine whether or not there is any clinical significance to these observations.

The centralized prenatal genetics screening program of New York City III: The first 7,000 cases

The Prenatal Diagnosis Laboratory of New York City (PDL) is a regional program for the prevention of genetic diseases. The administrative aspects of the establishment of the laboratory were described in papers I [Hsu, 1981] and II [Hsu and Benn, 1981] in this series. We now report our experience of the first 7,000 referrals to the laboratory. The laboratory achieved a success rate of 99.5% in obtaining a diagnosis. The frequency with which a repeat amniocentesis was required was 1.9%, usually attributable to inadequate initial amniotic fluid volume or condition. Cases were completed in an average time of 20.82 days. A total of 149 (2.13%) cytogenetic abnormalities were detected. There were 59 nonmosaic autosomal trisomies and 29 sex chromosome abnormalities. The incidence of unbalanced structural abnormalities (0.186%) was much higher than that reported in surveys of newborn infants largely because of the prenatal detection of cases with supernumerary chromosomes. The incidence of balanced structural abnormalities was also considerably higher than that found in surveys of the newborn population, in part because of the detection of subtle familial pericentric inversions of common chromosome regions (inv(Y)(p11q11), inv(2) (p11q13), and inv(1)(p11q13)). The incidence of cases with multiple independent chromosome abnormalities was no higher than expected by chance. A high incidence of mosaicism, pseudomosaicism, and maternal cell contamination was found. Screening for neural tube defects accounted for the detection of a further 16 abnormalities. Nearly all women with severely abnormal fetuses (trisomy 13, 18, 21) elected to terminate their pregnancy whereas only 62% of patients with a prenatally diagnosed sex chromosome abnormality elected to terminate their pregnancies. Full details of follow-up and confirmatory studies for unusual diagnoses are reported. Utilization of prenatal diagnosis in the New York City area has increased sharply since PDL became operational. The laboratory's success illustrates the role of a prenatal diagnosis laboratory that provides a service independent of the patient's financial status. The experience further shows the high degree of acceptance of prenatal diagnosis by individuals at high risk for a child with a genetic disorder.

Pericentric inversion of the Y chromosome and prenatal diagnosis

Pericentric inversion of the human Y chromosome has been estimated to occur with a frequency of 1-2 per thousand in various populations, and the results of this study, derived from over 12 000 prenatal diagnosis cases, is 1.15 per 1000. In these cases, it was concluded that there was no clinical significance because the fathers and male fetuses had the same pericentric inversion. Chromosome analysis of the father is advisable to determine whether or not the inversion is familial in order to be able to provide genetic counselling.

Incidence and significance of supernumerary marker chromosomes in prenatal diagnosis

The finding of a supernumerary marker chromosome in amniotic fluid cells poses a considerable counseling dilemma. In 6,500 cases referred to our laboratory over a 4 1/2-year period, eight such cases were identified (0.123% of all cases). In five of the eight cases, a diagnosis of true mosaicism between cells with 46 and 47 chromosomes was made. In the remaining three cases, the marker was present in 100% of the cells. In three cases, the marker was determined to be familial in nature with mosaicism present in the parents of two of these cases. Detailed cytogenetic findings for each case are provided. In no cases were abnormalities noted in either abortuses or live borns. The high incidence of mosaicism in these cases seems to indicate a propensity for supernumerary chromosomes to be lost. Familial markers may not be passed on for many generations, and they may arise as new mutations relatively frequently. There is an urgent need for more information on the risks associated with the prenatal detection of supernumerary chromosomes. We recommend that in considering the implications of the prenatal detection of marker chromosomes cases be considered in at least four distinct groups: type 1--familial and nonmosaic; type 2--familial with mosaicism in either the amniotic fluid cells, a parent, or both; type 3--de novo markers and nonmosaic; and type 4--de novo with mosaicism present in the amniotic fluid cells.

Maternal cell contamination of amniotic fluid cell cultures from two consecutive pregnancies complicated by fibroids

The detection of maternal cells in amniocyte cultures is thought to be due to the outgrowth of cells from small fragments of maternal tissue removed by the amniocentesis needle. An unusual case is reported in which maternal cell contamination (MCC) was found in the cell cultures from a woman in two different amniocenteses from two consecutive pregnancies. Both pregnancies were complicated by the presence of fibroids and the fibroid tissue may have been the source of the maternal cells. A history of an amniocentesis in which there was MCC of cell cultures, or the detection of fibroids, may pose an additional risk for MCC attributable misdiagnosis in prenatal genetic studies.

Reversion from deficiency of galactose-1-phosphate uridylytransferase (GALT) in an SV40-transformed human fibroblast line

Control SV40-transformed human fibroblasts can be readily adapted to growth on medium containing galactose as sole hexose source (galactose-MEH). However, most cells from a line of SV40-transformed skin fibroblasts from a patient with galactosemia (galactose-1-phosphate uridylyltransferase (GALT) deficiency) died in galactose-MEM. Surviving cells of this line either grew in completely sugar-free media or had acquired significant amounts of GALT activity. Two presumptive revertant cell lines with GALT activity were characterized in detail. The expression of GALT in these two lines was stable in nonselective conditions. Each had different reaction maximum velocities with respect to uridine diphosphoglucose (UDPg) concentration as compared to residual activity in the parental cell strain or control cells. Both appeared to demonstrate heat-inactivation profiles for GALT than differed from the parental cells or controls. UDPG concentration was found to significantly alter the thermostability of GALT. A competitive radioimmunoassay for GALT showed that these two lines had amounts of the GALT protein comparable to that of the parental cell strain or control cells. The electrophoretic mobility of GALT from the two presumptive revertants was found to differ from control cells. It was concluded that structural gene changes were probably responsible for the apparent reversion in these lines.

The centralized prenatal genetics screening program of New York City: II. Establishment of prenatal diagnosis laboratory

Prenatal diagnosis of genetic disorders is now being made available to an increasing number of New York City women through the establishment of a large centralized laboratory. This laboratory contracts to provide genetic diagnostic services to municipal and private hospitals throughout the New York City area. It is the first project of such magnitude in the United States. Prior to the receipt of samples for diagnostic purposes, the laboratory was required to meet the highest technical standards, as established by a Cytogenetics Advisory Committee. A set of guidelines was drawn up detailing the procedure and protocols for all the analyses and the reporting of results, including a timetable according to which results were to be obtained. The Cytogenetics Advisory Committee continues to review cases on a regular schedule. One of the unique aspects of the laboratory has been the development of back-up agreements with other area laboratories to assist in dealing with any problem that might disrupt the routine diagnostic service. The first year of operation of the laboratory has shown that financial, legal, and physical problems associated with designing and instituting a megacenter can be over-come. Similar programs should be encouraged.

Assignment of a gene for uridine diphosphate galactose-4-epimerase to human chromosome 1 by somatic cell hybridization, with evidence for a regional assignment to 1pter yields 1p21

The presence of human uridine diphosphate galactose-4-epimerase (GALE) was found to correlate with the presence of chromosome 1 in somatic cell hybrids between man and mouse. The gene for GALE can therefore be assigned to human chromosome 1. Using a chromosome 1 rearrangement, we have been able to regionally assign GALE to the pter yields p21 region.

Confirmation of the assignment of the gene for galactose-1-phosphate uridylyltransferase (E.C. 2.7.7.12) to human chromosome 9

The gene for galactose-1-phosphate uridylyltransferase (GALT) has previously been assigned to human chromosomes 2, 3, and 9. We have studied a further series of human-mouse hybrids and are able to confirm that the human gene for GALT is located on human chromosome 9.