Developmental defects, causes

Twelve or more additional triplet repeat diseases, many with neurological symptoms, have been identified (Table 26-4).405 407a These involve other trinucleotide repeats 5 -(GCG) , 5 -(CTG) , 5 -(GAA) , and 5 -(CAG) . In synpolydactyly, an inherited developmental defect causing malformation of hands and feet, an expansion of a GCG trinucleotide occurs within the gene HoxD 13. This results in incorporation of a polyalanine tract near the N terminus of the protein.408 Myotonic dystrophy DM1 (Box 19-A) results from expansion of CTG to 6 kbp or more within the untranslated 3 region of a gene for cAMP-dependent protein kinase.405 The mRNA transcripts accumulate... 

However, to characterize the developmental defects caused by auxin deficiency is also an important aspect of auxin biology [140-142],... 

Warfarin readily crosses the placenta. It can cause hemorrhage at any time during pregnancy as well as developmental defects when administered during the first trimester. Therefore, venous thromboembolic disease in pregnant women is generally treated with heparin, best administered by subcutaneous injection. 

Alaluusua S, Lukinmaa P-L, Vartiainen T, et al. 1996. Polychlorinated dibenzo-p-dioxins and dibenzofurans via mother s milk may cause developmental defects in the child s teeth. Environ Toxicol Pharmacol 1 193-197. 

Definitive evidence that dihydrotestosterone (DHT) is a potent androgen with its own important physiological and pathophysiological actions, separate from those of testosterone, was provided by two reports in 1974 of a rare inborn disorder of male phenotypic sexual differentiation caused by a deficiency in 5a-reductase, the enzyme that converts testosterone to DHT. The reduction in the conversion of testosterone to DHT by 5a-reductase, which underlies this syndrome, leads to a specific developmental defect in the formation of the male external genitalia and the prostate. Males with this genetic disorder exhibit a striking phenotype, in which the internal genitalia are normal... 

Known causes of reproductive and developmental disorders include genetic defects maternal metabolic imbalances infection and occupational, therapeutic, and environmental exposures to chemical and physical agents. This report primarily addresses reproductive and developmental defects that might be attributable to chemical and other agent occupational exposures. 

The causes of many developmental abnormalities are unknown. As an example, Nelson and Holmes (1989), through a careful evaluation of approximately 70,000 children and their families, were able to account for 57% of birth defects mutations (28%), multifactorial conditions (23%), uterine factors and twinning (3%), and exposure to chemical and physical agents found in the environment (3%). Thus, the etiology of at least 43% of all birth defects could not be determined. Prevention of developmental defects depends on understanding their causes and is important in reducing the tremendous societal and financial burden. 

Many kinds of organic or functional defects can lead to postovulatory reductions in fertility. For instance, anatomical impediments to gamete transport can prevent fertilization. Poorly developed or insufficient endometria due to end organ insensitivity to steroids, insufficient steroid hormone production, or impediments to steroid action at the level of the endometrium will not adequately support the implantation site of an otherwise healthy embryo. Previous reproductive tract infections are responsible for the majority of these kinds of reproductive failures however, developmental defects and alterations in organ function caused by inappropriate stimulation or response also contribute. 

Hirth, F., Therianos, S., Loop, T., Gehring, W.J., Reichert, H., Furukubo-Tokunaga, K. 1995. Developmental defects in brain segmentation caused by mutations of the homeobox gene orthodenticle and empty spiracles in Drosophila. Neuron 15, 769-778. 

In sows given rapeseed, it has been shown that the low iodine transfer via sows milk to piglets caused by rapeseed inhibition of iodide transport into the milk leads to hypothyroidism and developmental defects in the piglets, and that this is preventable by iodine administration (Schone et al.. 

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