**4.5. Developmental disorders**

Developmental disorders are ones in which the child develops slower than peers in areas such as motor function, social skills, and cognitive ability. Developmental disorders include Austism, Asperger's Syndrome, Attention Deficit Hyperactivity Disorder (ADHD), Rett Syndrome, and stereotypic movement disorder, to name a few. Gene expression profiling has been used extensively in Austism and genes involved in neuronal action potential, myelina‐ tion, axon ensheathment, cellular development, and cellular proliferation have been found to be differentially expressed in autistic children [153]. Another study, using an *in vitro* model of Autism found expression differences in genes involved in cell proliferation, neuronal differ‐ entiation, and synaptic assembly [154]. Similarly, a gene expression study in Rett Syndrome [155], which is a rare variant of Austism, has identified genes involved in mitochondrial functions, cellular protein metabolic processes, and RNA processing and DNA organization to be differentially regulated.

In addition to the applications listed here, gene expression profiling can be used in number of other human disorders such as diabetes, hypertension, psychiatric disorders, and infectious diseases.
