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.

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

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.

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Prenatal screening of cytogenetic anomalies - a Western Indian experience

Down's syndrome has an incidence of about 1.3 per 1000 births. Antenatal testing for this disorder on the basis of maternal age has been common practice (increasing age is associated with increasing risk of having an affected pregnancy). Since the late 1980s it has been possible to calculate a pregnancy-specific risk using maternal age and serum marker levels, but the absence of a national screening policy in the UK has resulted in a diversity of screening practice. Screening may take place in the first or second trimester of pregnancy, using maternal age in combination with up to six serum markers, with or without ultrasound markers. Additionally, some units offer the screen only to women in specific age groups. Risk and marker levels are affected by a number of factors for which adjustments in the calculation may be made. Laboratories offering screening must also establish robust monitoring and quality management systems to ensure continued confidence in the reported result. Current diagnostic techniques require the use of invasive procedures which pose a risk to the fetus and the mother. Future screening may combine new technologies with the identification of fetal cells in maternal blood to reduce or abolish the need for these procedures.

Current state of screening for Down's syndrome.

The aim of the investigation was to describe chromosomal inversions identified by a birth defects registry with respect to chromosomes involved, pregnancy outcome, method of diagnosis, inheritance, sex and 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 1986-2002. A total of 68 cases were identified through a statewide birth defects registry in Hawaii during 1986-2002. The chromosomes involved in the greatest proportion of inversions were chromosomes 6 (18%) and 9 (18%). Live births accounted for 62 (91%) of the cases. Diagnosis was made by amniocentesis or chorionic villus sampling in 60 (88%) of the cases. Of the 43 cases with known inheritance, the inversion was inherited in 40 (93%) and de novo in three (7%). Males accounted for 31 (46%) and females for 37 (54%) of the cases. Major structural birth defects were identified in 12 (18%) of the cases. Inversions diagnosed among infants and fetuses in Hawaii do not appear to affect all chromosomes equally. Most detected inversions occurred among live births and were inherited conditions. Infants and fetuses with inversions are not frequently associated with major structural birth defects.

Pattern of chromosomal inversions identified by a birth defects registry, Hawaii, 1986-2002.

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.

Patterns of chromosomal translocations identified by a birth defects registry, Hawaii, 1986-2000.

Child bearing at an early age and prenatal cytogenetic diagnosis in pregnant women of advanced age, combined with selective abortion, make it possible to avoid the birth of many children with serious chromosomal anomalies. To see how many of such births were still avoidable in Europe, data from 16 regional EUROCAT registers of congenital anomalies in nine EEC countries were analysed. In the period 1979-1982 about 30% of children with unbalanced anomalies of autosomes were born (live- and still-births) to mothers over 35 years of age. This amounts to an estimated 1300 cases yearly in the entire population of the nine countries. The approach shows the possible use of registry data for monitoring effects of avoidance strategies.

H. Dolk

Papers

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