الفهرس 
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Abstract
The typical course of development of language production skills occurs over an extended period of time from infancy through the teenage years and entails learning at many different levels: auditory perceptual linguistic and sensorimotor.
Language delay can be receptive, expressive, or a combination of both. A receptive language problem occurs when a child has difficulty understanding language. An expressive language disorder occurs when the child has difficulty expressing himself. These points can be identified as risk factors for language delays: being male having a low birth weight being born premature.
Causes of language delay: mental retardation, hearing loss, maturation delay (developmental language delay), expressive language disorder (developmental expressive aphasia), bilingualism, psychosocial deprivation, Autism, elective mutism, receptive aphasia and cerebral palsy. Mental retardation is the most common cause of language delay, accounting for more than 50 percent of cases .Abused children have an increased incidence of language delay .Autistic children, in general, fail to make eye contact, smile socially, respond to being hugged or use gestures to communicate.
The development of the brain is orchestrated, tightly regulated and genetically encoded process with clear influence from the environment. This suggests that any deviation from this program early in life can result in neurodevelopmental disorders and depending on specific timing, might lead to distinct pathology later in life. Because of that, there are many causes of neurodevelopmental disorder, which can range from deprivation, genetic and metabolic diseases, immune disorders, infectious
diseases, nutritional factors, physical trauma, toxic and environmental factors.
Some neurodevelopmental disorders such as autism and other autistic spectrum disorders—are considered multifactorial syndromes (with many causes but more specific neurodevelopmental manifestation).
So G6PD deficiency, as metabolic disease, an X-linked disorder, is the most common enzymatic disorder of red blood cells in humans, affecting more than 400 million people worldwide.
Individuals deficient in G6PD after exposure to chemicals (for example, naphthalene) and drugs (including sulfamides, antipyretics, nitrofurane, primaquine and chloroquine) can induce massive intravascular hemolysis. Among the clinical forms of this enzymatic deficiency are jaundice, acute hemolytic anemia and chronic nonspherocytic hemolytic anemia. A more severe consequence of neonatal hyperbilirubinemia is kernicterus, a neurological syndrome caused by the deposition of bilirubin in the brain tissues which leads to global developmental delay and intellectual disability.
Global developmental delay and intellectual disability also can result from disorders of metabolism. These disorders happen when the genes that make metabolic enzymes are abnormal.. In one group of disorders, known as inborn errors of metabolism (IEM), some studies suggest screening tests give positive results in about 1.8 percent to 5 percent of children tested. In another group of disorders, known as congenital disorders of glycosylation, studies suggest that screening tests give positive results in about 1.4 percent of children tested.
A child may be described as having global developmental delay (GDD) if they have reached two or more milestones in all areas of development (called developmental domains). These areas are:
• Motor skills - either gross motor skills like sitting up or rolling over and fine motor skills, for example picking up small objects.
• speech and language - which also includes babbling, imitating speech and identifying sounds, as well as understanding what other people are trying to communicate to them.
• Cognitive skills - the ability to learn new things, process information, organize their thoughts and remember things.
• Social and emotional skills - interacting with others and development of personal traits and feelings, as well as starting to understanding and respond to the needs and feelings of others.
Glucose-6-phosphate dehydrogenase deficiency is the most prevalent enzyme deficiency, with an estimated 400 million people affected worldwide .Selected studies included cross-sectional and longitudinal studies published between 1960 and 2008. Additionally, meta-analytic procedures were employed to assess the degree of heterogeneity amongst prevalence estimates and, where appropriate, pool them. The searches yielded a total of 280 prevalence estimates, corresponding to 88 countries. The highest prevalence rates were reported among Sub-Saharan African countries, even after adjusting for assessment method
Developmental disabilities are relatively common in children, with 5-10% prevalence. GDD is estimated to be prevalent in 1-3% children < 5 yr., and it is estimated that between 40,000 - 120,000 children born each year in the U.S. and Canada will manifest GDD. There are many possible
causes for the clinical picture of GDD and some causes are treatable. Therefore, early recognition and diagnosis is important. In addition, some of the etiologies are genetically transmitted and may affect future family members. An underlying etiology can be identified in approx. 25% of cases of developmental delay, with higher rates (50%) in GDD and motor delays, and lower rates (<5%) in children with isolated language disorders.