Developmental change may result from genetically-controlled processes called maturation or as a result of learning and environmental factors but mostly involves an interaction between these two factors. There are various definitions given to periods in child development as each period is a continuum affected by individual differences concerning start and ending. Some age-related defined intervals and development periods are: newborn t the ages 0 to 1 month; infant at ages of 1 month to 1 year; preschooler (age’s 4–6years) and adolescent between 13 and 20 years (Kail RE 2006).  However, organizations such as the World Association for Infant Mental Health use the term infant as a broad category to define children from birth to the age of 3 years. The optimal development of children is of great significant to the society and therefore it is vital to understand the cognitive, educational, social and emotional development of children.

Disorders of neural development, is defined as the impairment of growth and development of the central nervous system or the brain. The term is used narrowly to refer to a brain function disorder which affects learning ability, memory and emotion and which manifests as the individual grows (Reynolds and Cecil R. 1999). Disorders considered to have a neurodevelopment  origin or to have consequences on  neural developmental  when they occur at infancy and childhood include autism and autism spectrum disorders like  Asperger syndrome, Rett syndrome,  genetic disorders like fragile-X syndrome,  epilepsy and Down syndrome , learning disorders ,fetal alcohol syndrome, neurological and psychiatric disorders.  The neurodevelopment disorders are widely associated with varying degrees of physical, mental, emotional and economic burden to families, individuals and society in general (Cecil R. and Reynolds 1999).Autism  spectrum disorder (ASD) or classical ASD Autistic disorder or autism is a range of complex disorders which affect  neuron development and is characterized by difficulties in communication, social impairments, and repetitive restricted, as well as   patterns of stereotype behavior. Other rare, very severe disorders that are included in the autism spectrum disorders are Rett syndrome and childhood disintegrative disorder (Powers MD 2000).

Autistic disorder or autism is the most severe form of ASD, with other conditions along the spectrum including a milder form called Asperger syndrome, Rett syndrome which is a rare condition, childhood disintegrative disorder and pervasive developmental disorder in which a child shows symptoms of either of these autistic disorders, but the symptoms do not meet the specific criteria for either and hence it is referred to as pervasive developmental disorder not otherwise specified (PDD-NOS)(Powers MD (2000).

Prevalence

ASD occurs in all ethnic and socioeconomic groups with significant variations in severity and character. The most recent government survey on the rate of autism was in 2007 in which the Centers for Disease Control (CDC) found the rate to be higher than the rates found from studies conducted in early 1990s in the United States. The CDC survey was conducted in 14 communities throughout U.S in which diagnosis of autism spectrum disorder was assigned based on school and health records of 8 year olds. The CDC report also confirms other recent epidemiologic studies which have documented that more children are being diagnosed with ASD than in the past. The rte of SD was found out in data from an earlier report of the CDC’s Atlanta-based program to be 3.4 per 1,000 for children aged between 3 and 10 years .from   Summary of this and several other major studies on the prevalence of autism, CDC estimates that 2-6 per 1,000 children have an ASD with males risk being 3-4 times higher than females (Yeargin-Allsopp M. 2003).

Rett Syndrome

Rett syndrome is severe but relatively rare, affecting females almost exclusively, one out of 10,000 to 15,000.  Autism –like symptoms start appearing after a period of normal development, sometime the period between 6montths and 18 months. The girl’s mental and social development regress end hence she does not respond to her parents anymore and pulls away from all social contacts.  She cannot control her feet; she stops talking and wrings her hands (Yeargin-Allsopp M. 2003). .