Frequency of births with potentially avoidable serious chromosomal anomalies in EEC countries, 1979-1982

Prenatal screening of cytogenetic anomalies - a Western Indian experience

Background

Children born with congenital anomalies present a very high rate of perinatal death and neonatal mortality. Cytogenetic analysis is a convincing investigation along with clinical suspicion and biochemical screening tests. The current study was designed to characterize the prevalence and types of chromosomal abnormalities in high risk prenatal samples using different cytogenetic techniques.

Methods

This study was conducted on a total of 1,728 prenatal samples (1,324 amniotic fluids, 366 chorionic villi and 38 cord blood samples) from 1994 to 2014 at Institute of Human Genetics, Ahmedabad, India. Conventional karyotyping was conducted with GTG-banding. Molecular approaches were used (fluorescence in situ hybridization = FISH and/ or array-comparative genomic hybridization = aCGH) when indicated to detect karyotypic abnormalities.

Results

Abnormal karyotypes were detected in 125/1,728 (7.2%) cases. Trisomy 21 was the most common abnormality detected in 46 (2.7%) followed by trisomy 18 in 11 (0.6%) and trisomy 13 in 2 (0.1%) samples. Besides, structural abnormalities such as reciprocal and Robertsonian translocation were detected in 20 [1.2%] cases. Turner syndrome was diagnosed in seven (0.4%) cases; in six (0.34%) cases there was an inversion in the Y-chromosome. Heteromorphic variants were diagnosed in 22 (1.3%) cases. Finally, small supernumerary marker chromosomes (sSMC) were found in six (0.34%) cases.

Conclusion

Conventional GTG-banding along with molecular cytogenetic techniques is useful in detecting genomic alterations and rearrangements. Comprehensive characterization of chromosomal rearrangements like sSMC has the potential to save potentially healthy fetuses from being terminated.

Rare chromosome abnormalities, prevalence and prenatal diagnosis rates from population-based congenital anomaly registers in Europe

The aim of this study is to quantify the prevalence and types of rare chromosome abnormalities (RCAs) in Europe for 2000-2006 inclusive, and to describe prenatal diagnosis rates and pregnancy outcome. Data held by the European Surveillance of Congenital Anomalies database were analysed on all the cases from 16 population-based registries in 11 European countries diagnosed prenatally or before 1 year of age, and delivered between 2000 and 2006. Cases were all unbalanced chromosome abnormalities and included live births, fetal deaths from 20 weeks gestation and terminations of pregnancy for fetal anomaly. There were 10,323 cases with a chromosome abnormality, giving a total birth prevalence rate of 43.8/10,000 births. Of these, 7335 cases had trisomy 21,18 or 13, giving individual prevalence rates of 23.0, 5.9 and 2.3/10,000 births, respectively (53, 13 and 5% of all reported chromosome errors, respectively). In all, 473 cases (5%) had a sex chromosome trisomy, and 778 (8%) had 45,X, giving prevalence rates of 2.0 and 3.3/10,000 births, respectively. There were 1,737 RCA cases (17%), giving a prevalence of 7.4/10,000 births. These included triploidy, other trisomies, marker chromosomes, unbalanced translocations, deletions and duplications. There was a wide variation between the registers in both the overall prenatal diagnosis rate of RCA, an average of 65% (range 5-92%) and the prevalence of RCA (range 2.4-12.9/10,000 births). In all, 49% were liveborn. The data provide the prevalence of families currently requiring specialised genetic counselling services in the perinatal period for these conditions and, for some, long-term care.

Patterns of chromosomal deletions identified by a birth defects registry, Hawaii, 1986-2003

The aim of the investigation was to describe the chromosomal deletions identified by a birth defects registry with respect to the chromosomes involved, pregnancy outcome, method of diagnosis, inheritance, sex, and the diagnosis of major structural birth defects. Cases were derived from a population-based birth defects registry in Hawaii and comprised all infants and fetuses with chromosomal deletions delivered during 1986-2003. A total of 71 cases were identified through a statewide birth defects registry in Hawaii during 1986-2003. The chromosomes involved in the greatest proportion of deletions were chromosomes 22 (14.1%), 4 (11.3%), and 5 (11.3%). Live births accounted for 58 (81.7%) of the cases. Diagnosis was made by amniocentesis or chorionic villus sampling in 19 (26.8%) of the cases. Of the 18 cases with known inheritance, the deletion was inherited in 5 (27.8%) and de novo in 13 (72.2%). Males accounted for 28 (39.4%) and females for 43 (60.6%) of the cases. Major structural birth defects were identified in 51 (71.8%) of the cases. Chromosomal deletions do not appear to affect all chromosomes equally. Most of the chromosomal deletions that were detected occurred among live births and were de novo conditions. Infants and fetuses with chromosomal deletions are more likely to be females and to be associated with major structural birth defects.

Patterns of Chromosomal Translocations Identified by a Birth Defects Registry, Hawaii, 1986–2000

Using a birth defects registry, this investigation examined the distribution of translocations by type of translocation, chromosomes involved in the translocation, pregnancy outcome, method of diagnosis, inheritance, and diagnosis of major structural birth defects. A total of 121 cases were identified through a statewide population-based birth defects registry. The translocations were reciprocal in 89 (73.6%) cases, Robertsonian in 32 (26.4%) cases, balanced in 86 (71.1%) cases, and unbalanced in 35 (28.9%) cases. Live births accounted for 76 (88.4%) of balanced translocations and 22 (62.9%) of unbalanced translocations. Diagnosis was made by amniocentesis or chorionic villus sampling in 72 (83.7%) of balanced translocations and 11 (31.4%) of unbalanced translocations. Of cases of known inheritance, the translocation was of maternal origin in 38 (46.3%) cases, paternal origin in 25 (30.5%) cases, and de novo in 19 (23.2%) cases. Major structural birth defects were diagnosed in 17 (19.8%) of balanced translocations and 20 (57.1%) of unbalanced translocations. Translocations were more likely to be reciprocal, balanced, and of maternal origin. Infants and fetuses with unbalanced translocations were less likely to be live births and diagnosed by amniocentesis or chorionic villus sampling and more likely to be diagnosed with major structural birth defects.