The extra copies of key chromosome 21 genes underlie their increased susceptibility to AMKL by promoting the development of a certain type of inactivating mutation in the GATA1 gene. The GATA1 gene resides on the X chromosome and codes for two transcription factors, GATA1 and a shorter version, GATA1-S. GATA1 and GATA1-S contribute to regulating the expression of genes that control the maturation of megakaryoblasts to promegakaryocytes, megakaryocytes, and platelets as well as the maturation of erythroblasts to red blood cells. GATA1-S appears less active than GATA1 in controlling some of the genes that promote megakaryoblast maturation but more active than GATA1 in stimulating megakaryoblast proliferation. Various GATA1 mutations that cause this gene to make GATA1-S but unable to make GATA1 result in the excessive proliferation of platelet precursor cells, reductions in the levels of circulating blood platelets, mild reductions in the levels of circulating red blood cells, and the development of transient myeloproliferative disease (TMD). TMD is a disorder involving the excessive proliferation of non-malignant megakaryoblasts and descendent cells due to the cited truncating mutations in the GATA1 gene. TMD is a necessary predecessor to DS-AMKL.Down syndrome fetuses and neonates with one of the cited types of GATA1 truncating mutations are in rare cases asymptomatic (i.e. silent TMD) but more commonly exhibit in utero or during the first months of live accumulations of immature megakaryoblasts in, and sometimes life-threatening injury to, the fetal blood-forming organ, the liver, and other tissues.
Ophthalmia nodosa is a cutaneous condition characterized by inflammation of the eye due to lodging of (for example) caterpillar hairs in the conjunctiva, cornea, or iris. See also
Bristleworm sting
List of cutaneous conditions


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