The affected individual may inherit an extra part of chromosome 21 or an entire extra copy of chromosome 21, a condition known as trisomy British physician John Langdon Down first described the physical features of Down syndrome in , and thus the disorder was later named for him. The physical and cognitive impacts of Down syndrome range from mild to severe. Some common physical signs of the disorder include a small head, flattened face, short neck, up-slanted eyes, low-set ears, enlarged tongue and lips , and sloping underchin.
This paper shows that some individuals with Down syndrome are capable of producing, imitating repeating and comprehending passive sentences, even though group studies indicate that this is not the norm. Experimental tests of elicited production, repetition and comprehension of passive and active sentences applied in ten adolescents with Down syndrome, speakers of Portuguese, showed that out of the ten adolescents, one, Fa, is able to produce, imitate and comprehend passive sentences. This hypothesis is strong inasmuch as it assumes that both active and passive have very similar initial derivations. There is not, however, strong evidence that the nine adolescents interpret the passive as active. Fa, on the other hand, does not interpret the passive as active, as she produces, imitates and comprehends the passive structure very well. Rubin, M. Down Syndrome Research and Practice , 11 2 ,
As they age, those affected by Down syndrome have a greatly increased risk of developing a type of dementia that's either the same as or very similar to Alzheimer's disease. Down syndrome — also known as trisomy 21 — is a condition in which a person is born with extra genetic material from chromosome 21, one of the 23 human chromosomes. Most people with Down syndrome have a full extra copy of chromosome 21, and so they have three copies instead of the usual two. Scientists think the extra copy results from a random error in the specialized cell division that produces eggs and sperm.