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The prevalence of trisomy 21 has been reported to differ by race–ethnicity, however, the results are inconsistent and the cause of the differences is unknown. Using data from 1996 to 2005 from the Metropolitan Atlanta Congenital Defects Program (MACDP), we analyzed the use of prenatal cytogenetic testing and the subsequent use of elective termination among pregnancies affected with any MACDP-eligible birth defect and trisomy 21, by maternal race–ethnicity. We then examined whether these factors could explain the observed differences in the prevalence of trisomy 21 among race–ethnicity groups. Among all pregnancies with birth defects, prenatal cytogenetic testing as well as elective terminations after an abnormal prenatal cytogenetic test result were observed less frequently among Hispanic women than among non-Hispanic white women (odds ratio [OR] 0.66, 95% confidence interval [CI] 0.56–0.78, respectively). In pregnancies affected by trisomy 21, both the Hispanic and the non-Hispanic black populations had more live births (89.5% and 77.8%, respectively) and fewer elective terminations (5.7% and 15.2%, respectively) compared to the non-Hispanic white population (63.0% live births, 32.3% elective terminations). After adjusting for elective terminations, non-Hispanic white mothers had a higher live birth prevalence of trisomy 21 compared to non-Hispanic black (OR 0.64, 95% CI 0.54–0.76) or Hispanic mothers (OR 0.69, 95% CI 0.55–0.86). Overall, our data suggest that factors associated with decisions made about the use of prenatal testing, and about pregnancy management after testing, might play a large role in the race–ethnicity differences observed in the live birth prevalence of trisomy 21. © 2013 Wiley Periodicals, Inc.

The annual National Birth Defects Prevention Network (NBDPN) Congenital Malformations Surveillance Report includes state-level data on major birth defects (i.e., conditions present at birth that cause adverse structural changes in one or more parts of the body) and a directory of population-based birth defects surveillance systems in the United States. Beginning in 2012, these annually updated data and directory information are available in an electronic format accompanied by a data brief. This year’s report includes data from 41 population-based birth defects surveillance programs and a data brief highlighting the more common trisomy conditions (i.e., disorders characterized by an additional chromosome): trisomy 21 (commonly referred to as Down syndrome), trisomy 18, and trisomy 13. State-Specific Data Collection and Presentation for Selected Birth Defects Data collection The NBDPN Data Committee, in collaboration with the Centers for Disease Control and Prevention (CDC), invited population-based birth defects surveillance programs in the United States to submit data on major birth defects affecting central nervous, eye, ear, cardiovascular, orofacial, gastrointestinal, genitourinary, and musculoskeletal systems, as well as trisomies, amniotic bands, and fetal alcohol syndrome. Table 1 lists these 47 conditions and their diagnostic codes (International Classification of Diseases, 9th Revision, Clinical Modification [ICD-9-CM]; and Centers for Disease Control and Prevention/British Pediatric Association Classification of Diseases [CDC/BPA]). Table 1 ICD-9-CM and CDC/BPA Codes for 47 Birth Defects Reported in the NBDPN Annual Report Participating state birth defects programs provided counts of all cases of the birth defects listed in Table 1 as well as counts of live births and male live births in their catchment areas for births occurring from January 1, 2006 through December 31, 2010. The cases for all defects were reported by maternal census race/ethnic categories: White non-Hispanic, Black/African-American non-Hispanic, Hispanic, Asian/Pacific Islander non-Hispanic, American Indian/Alaska Native non-Hispanic. Additionally, trisomy cases were provided by six categories of maternal age at delivery: less than 20 years, 20 to 24 years, 25 to 29 years, 30 to 34 years, 35 to 39 years, and 40+ years.

The purpose of this study was to examine changes in the use of cytogenetic testing and identification of chromosomal abnormalities among pregnancies and children with birth defects. Utilizing data from 1968 to 2005 from the Metropolitan Atlanta Congenital Defects Program, we analyzed trends in the frequency and timing (prenatal or postnatal) of cytogenetic testing and the prevalence of recognized chromosome abnormalities among pregnancies and children with birth defects (n = 51,424). Cytogenetic testing of pregnancies and children with birth defects increased from 7.2% in 1968 to 25.0% in 2005, as did the identification of chromosomal abnormalities (2.2% in 1968 to 6.8% in 2005). The use of prenatal cytogenetic testing decreased from 1996 to 2005 among women aged ≥35 years. Identification of chromosomal abnormalities in pregnancies and children with birth defects increased from 1968 to 2005, possibly due to increased testing, improved diagnostic techniques, or increasing maternal age. The decline in prenatal cytogenetic testing observed among mothers aged ≥35 years may be related to the availability of improved prenatal screening techniques, resulting in a reduction in the utilization of invasive diagnostic tests. Published 2011. This article is a U.S. Government work and is in the public domain in the USA.

For decades, classical cytogenetic techniques that yielded a karyotype were the mainstay for identifying and characterizing the causes of certain genetic syndromes and birth defects. The capacity to identify chromosome anomalies expanded in the late 1980s and the 1990s with the development and maturation of fluorescent in situ hybridization (FISH) techniques to interrogate submicroscopic regions of the chromosomes for deletions or duplications. Beyond karyotypes and FISH, new technologies—chromosomal microarrays and next generation DNA sequencing—have markedly increased the number of birth defects and genetic syndromes that now have a known cause. These new testing techniques that can unambiguously confirm a diagnosis—as occurred previously, for example, with FISH for 22q11.2 deletions—will increase the specificity and sensitivity for classifying birth defects and improve prevalence estimates. Although these testing techniques improve the resolution of analysis of smaller and more complex chromosome and DNA anomalies, their interpretation can be problematic, particularly when the test results are of unknown significance. Broader usage of new prenatal screening technologies, such as testing for chromosome and DNA anomalies in cell-free fetal DNA, will likely impact prevalence estimates of certain birth defects included in surveillance systems. These new advancements in genetic testing can create challenges for birth defects surveillance and research programs in learning how to abstract, interpret, classify, store, and incorporate new findings into surveillance systems, as well as categorizing the data in epidemiological studies. Birth defects research and surveillance programs must be mindful of these new challenges and thoughtful in addressing them.

Chromosome rearrangements are a significant cause of intellectual disability and birth defects. Subtelomeric rearrangements, including deletions, duplications and translocations of chromosome ends, were first discovered over 40 years ago and are now recognized as being responsible for several genetic syndromes. Unlike the deletions and duplications that cause some genomic disorders, subtelomeric rearrangements do not typically have recurrent breakpoints and involve many different chromosome ends. To capture the molecular mechanisms responsible for this heterogeneous class of chromosome abnormality, we coupled high-resolution array CGH with breakpoint junction sequencing of a diverse collection of subtelomeric rearrangements. We analyzed 102 breakpoints corresponding to 78 rearrangements involving 28 chromosome ends. Sequencing 21 breakpoint junctions revealed signatures of non-homologous end-joining, non-allelic homologous recombination between interspersed repeats and DNA replication processes. Thus, subtelomeric rearrangements arise from diverse mutational mechanisms. In addition, we find hotspots of subtelomeric breakage at the end of chromosomes 9q and 22q; these sites may correspond to genomic regions that are particularly susceptible to double-strand breaks. Finally, fine-mapping the smallest subtelomeric rearrangements has narrowed the critical regions for some chromosomal disorders.

Worldwide, an estimated 7.9 million children are affected by congenital and inherited disorders. Some disorders are relatively common, affecting tens of thousands of newborns annually; others are rare, involving disorders that, in extreme cases, can affect less than 30 infants per year. However, this infrequency does not reduce the impact or burden on individuals and their families. Congenital defects can cause long-term disability, have a lifelong impact on health, and cost billions of dollars in care. Collection of population-based surveillance data ideally enables the discovery of etiologies for rare congenital disorders of unknown cause, allows for examining outcomes, and evaluating treatments and interventions for children with all types of congenital and inherited disorders. Many challenges are associated with performing population-based surveillance, such as difficulty in ascertaining appropriate diagnoses and frequent unavailability of necessary resources. This chapter focuses on the importance of population-based data and uses national and international surveillance systems as models for how these rare disorders can be better understood.

Worldwide, an estimated 7.9 million children are affected by congenital and inherited disorders. Some disorders are relatively common, affecting tens of thousands of newborns annually; others are rare, involving disorders that, in extreme cases, can affect less than 30 infants per year. However, this infrequency does not reduce the impact or burden on individuals and their families. Congenital defects can cause long-term disability, have a lifelong impact on health, and cost billions of dollars in care. Collection of population-based surveillance data ideally enables the discovery of etiologies for rare congenital disorders of unknown cause, allows for examining outcomes, and evaluating treatments and interventions for children with all types of congenital and inherited disorders. Many challenges are associated with performing population-based surveillance, such as difficulty in ascertaining appropriate diagnoses and frequent unavailability of necessary resources. This chapter focuses on the importance of population-based data and uses national and international surveillance systems as models for how these rare disorders can be better understood.

In both humans and mice there are numerous reports of Y chromosome abnormalities that interfere with sex determination. Recent studies in the mouse of one such mutation have identified Y chromosome nondisjunction during preimplantation development as the cause of abnormal testis determination that results in a high frequency of true hermaphroditism. We report here that the mouse Y chromosome from the A/HeJ inbred strain induces similar aberrations in sex determination. Our analyses provide evidence, however, that the mechanism underlying these aberrations is not Y chromosome nondisjunction. On the basis of our findings, we postulate that a mutation at or near the centromere affects both the segregation and sex-determining properties of the A/HeJ Y chromosome. This Y chromosome adds to the growing list of Y chromosome aberrations in humans and mice. In both species, the centromere of the Y is structurally and morphologically distinct from the centromeres of all other chromosomes. We conclude that these centromeric features make the human and mouse Y chromosomes extremely sensitive to minor structural alterations, and that our studies provide yet another example of a good Y chromosome gone ‘bad.’