Down syndrome is the most common genetic disorder in children. The genotype involves an extra copy of the short arm of chromosome 21, either as trisomy (95% of cases), a translocation, or expressed mosaicly. This condition is not inherited and occurrs on average in about 1 in 800 live births in the United States. Incidence increases as maternal and paternal age increase. Down syndrome affects almost every system in the body. For example, brain size is smaller in adults though the same size at birth, 50% of these children have significant heart defects requiring surgery, neuronal density in the brain is significantly reduced, middle ear infection persists into adulthood, hypotonia ranges from mild to severe, and cognitive performance ranges from normal performance to severe mental retardation. The remainder of this article will summarize the specific speech, language and communication features associated with this syndrome.

The unique features of speech, language, and hearing ability of children with Down syndrome have been detailed by Miller, Leddy, and Leavitt (1999). First is the frequent hearing loss in infants and children, with more than 75% of young children found to have at least a mild hearing problem at sometime in childhood. These hearing problems can fluctuate, but about one-third of children have recurring problems throughout early childhood that can lead to greater language and speech delay. These results suggest particular attention be directed to monitoring responsiveness to everyday speech and frequent hearing testing through childhood. Second, there are unique verbal language characteristics of persons with Down syndrome. Children experience slower development of language relative to other cognitive skills. Communication performance is characterized by better language comprehension than production. Vocabulary use is better than the mastery of the grammar of the language. Progress in speech and language performance is linked to several related factors, including hearing status, speech-motor function status, and advancing cognitive skills associated with a stimulating verbal and nonverbal environment. Progress in speech, language, and communication should be expected beyond early childhood through adolescents (Chapman, Hesketh, and Kistler, 2002). A third unique feature is a protracted period of unintelligible speech. Speech intelligibility is a persistent problem of persons with Down syndrome through late childhood. Most family members have some difficulty understanding the speech of their children in everyday communication. Treatment protocols can improve speech intelligibility, leading to improved communication of children and adults. Finally, the development of writing and literacy skills in persons with Down syndrome should be expected. Children participating in early reading and writing experiences experience better communication and academic skills than their peers with less literacy experience. Early reading programs have been successful at teaching sight word vocabulary to children as young as 3 years of age.