Human Genetics & Embryology

A defective CYP21A2 gene downstream of the TNXB gene in congenital adrenal hyperplasia (CAH) falls into three categories: (a) small-scale conversions of CYP21A1P, (b) spontaneous mutations, and (c) chimeric RCCX modules that include the chimeric CYP21A1P/ CYP21A2 and TNXA/TNXB genes [1]. Most of the CYP21A2 mutations identified so far were a result of small-scale conversions of the CYP21A1P (up to 11 for CYP21A1P) during both meiosis and mitosis [2], which account for about 70%-80% of all CAH cases. The Chimeric CYP21A1P/CYP21A2 and TNXA/TNXB genes, which result from unequal cross-over (or deletions) during meiosis [2] and occur in ~20% of CAH alleles in most populations [1,3] respectively reflect the deletion of the 1/XCYP21A1P - XA - RP2 - C4B - 1/XCYP21A2 gene array (1/X indicates an uncertain fraction of the gene sequence) [1] and a deletion of the RP2 - C4B - CYP21A2 - 1/XTXNB gene array [1]. Their deletion range is about a 26- or 32-kb gene sequence which depends on whether C4B is the long or short gene (more commonly shown in the literature as being 30 kb). In fact, these different types of large-gene deletions in the RCCX region are generally considered to represent one event in many studies.

Abstract
Objective: To test the hypothesis that embryos reaching a certain developmental stage at a fixed time point (indicative of growth rate) and those of better morphology are more likely to be euploid than those reaching an earlier stage at the same point and those with poorer morphology. To test the hypothesis that quality of the inner cell mass (ICM) and trophectoderm (TE) independently predict ploidy status. 5 specific age groups were tested
Design: Observational research study, retrospective analysis
Setting: Clinical IVF laboratory, comprehensive chromosome screening (CCS) outsourced to specialist laboratory
Patients: Those undergoing IVF with Comprehensive Chromosome Testing (CCS) by array Comparative Genomic Hybridization (aCGH).
Interventions: All embryos grown to day 5 and 6. Those that formed advanced blastocysts were biopsied and cells were analyzed using aCGH
Main Outcome Measures: developmental stage reached by a fixed time point and morphology of whole embryos and quality of ICM and TE; correlation to rates of aneuploidy for all chromosomes.
Results: In addition to confirming a maternal age effect, evidence suggested that embryos reaching a more advanced stage of development on day 5 were more likely to be chromosomally normal than those not reaching the same stage until day 6. The poorer quality embryos were more likely to be aneuploid in the most age groups but this effect was seen more markedly in the trophectoderm (TE) than the inner cell mass.
Conclusions: When comparing aneuploidy to growth rate, a complex pattern emerges in that, in the whole data set, it is the slower growing embryos that appear to be more likely to be aneuploid (but only in the younger and older age groups). By isolating the slower growing cohort (those not ready to biopsy until day 6) however, it seems that the relatively faster ones that continue to grow to day 6 are more likely to be aneuploid. Moreover, TE quality appears to be an important consideration for choosing embryos in all age groups.

The appearance of a second edition of this work testifies to the rapid changes that have occurred since the first edition was published in 2008. The wide-ranging scope of this book is revealed in its secondary title: ”The Environmental Regulation of Development, Health and Evolution”. The eleven chapters, four appendices and a coda of philosophical concerns raised by ecological developmental biology engender an extensive purview of the subject. It delves into the newly developing science of “eco- devo” whereby environmental agents impact upon genetic inheritance patterns of a wide range of biota. The book integrates the medical studies of diabetes, cancers, obesity and the aging process into the environmental influences on the occurrences of diseases and infirmities. Herein, the impact of teratogens, endocrine disruptions and diet upon development is explored and explained