Pleiotropy

Many pleiotropic conditions arise from genes whose products are involved in signaling and regulation pathways. Because these proteins coordinate daily life in numerous tissues, defects in them have numerous consequences, as one breakdown leads to another.

Myotonic dystrophy is another autosomal dominant disorder. A gene for a protein—a kinase, involved in signalling and communication within the cell—is burdened with up to three thousand extra pieces of DNA. The extra DNA comes from trinucleotides (CTG)_n that are added by mistake during DNA duplication, both in germ line cells and during early cell divisions The café-au-lait spots typical of neurofibromatosis are evident on this patient's hand. in the embryo. During transcription and translation, the kinase is not put together right, and the kinase's work in muscles goes badly. Muscles contract but cannot relax quickly. Young persons may have heart attacks, generalized muscle weakness, and loss of bulk. Swallowing and speech is hard, due to weak muscles in the tongue and neck. Other pleiotropic effects include baldness, cataracts, and changes in intelligence.

Pleiotropic outcomes are common with hormones. Hormones are signals that create multiple responses in tissues that carry receptors for them. The receptor binds to the hormone and triggers a cascade of reactions inside the cell. A defective receptor loses or misinterprets the signal. When the hormone insulin meets defective insulin receptors on an individual's cells, the person is more likely to develop type II diabetes. Cells do not open their gateways to let sugar in from the bloodstream, and the cells almost starve to death in the midst of plenty. Meanwhile, sugar accumulates in the blood and causes all sorts of ramifications for blood circulation, and it damages capillaries in all areas, from kidneys, to eyes, to feet. Gangrene, mental disturbances, kidney failure, and blindness can and do occur. Diminished give-and-take of sugar molecules across cell membranes leads to the multifaceted disease diabetes.