In the 20th century, a small elite group of scientists who decided to study the aspects of mental retardation were found in a confusing situation making their research difficult (Hywood, 1996, p.33) as since an approximately 1-3 out each 100 people suffer from mental retardation (Winnepenninck at el, 2003, p.2). There was lots of dispute concerning the explanation of mental retardation and till now it remains an interested topic (Chelly at el, 2006, p.1). In agreement with the “American association on mental retardation”, mental retardation is a condition of being unable to perform a sequence of physical, mental and social activities during the childhood till the age of 18 (Causes of retardation, 2005, p.1).
In general mental retardation is pointed out by an IQ below 70 (Chelly at el, 2006, p.2). Based on IQ, there are two types of mental retardation: the “mild” mental retardation accompanied by an IQ in the interval of 50 and 70, and the “severe” mental retardation with an IQ less than 50 (Chelly at el, 2006, p.2). Soon after, this unfavorable condition could be detected by intelligence and behavioral test (Causes of retardation, 2005, p.1). Afterwards, the mentally retarded person dismisses from consideration the rest of the world and manifests kinds of attachment to their private life (Masland at el, n.d, and p.56).
In reality, the strong unfavorable effect of mental retardation on the population makes the detection of the causes of this abnormal functioning indispensable (Winnepenninck at el, 2003, p.3). This is because the perfect knowledge of any abnormal functioning needs the assumption of the causes of the disease (Masland at el, n.d, p.29). There are many genetic, behavioral, and psychosocial causes as to why mental retardation is increasing over the world.
Mental Retardation 4 The primary cause of mental retardation depends on genetics which give careful consideration to heredity and agree with the concept that traits are transmitted from generation to generation. From the fact that the brain is a complicated structure, genetic diseases give rise to approximately half of “severe” mental retardation. Simultaneously, mental retardation, health complications and abnormal development are the result of genetic disorders (Genetic causes, n.d, p.p 1-2 ) which are the issue of disturbance of genes caused by infections and other factors (Causes of retardation, 2005, p.1) . These genetic disorders are not necessarily hereditary and may not have fix symptoms (Genetics, 2005, p.2). Eventually, more than 7000 genetic diseases are established and they can be divided into three categories (Genetic causes, n.d, p.p 1-2): Imprinted gene deregulation, monogenic causes, and chromosomal abnormalities.
First, in the discussion of imprinted gene it is necessary to begin by defining this expression. Genes expressed from only one parent are called genomic imprinting and these genes grow in the genome and have effects on some parts of chromosome 7,11,14 and 15. Disorders in these genes are several and mostly occur during diseases. Besides, this deregulation includes two important syndromes: The Angelman’s and the Prader-Willi (Chelly et al, 2006, p.2).
“A paternal deletion gives rise to features of the Prader-Willi syndrome and a maternal deletion gives rise to features of Angelman syndrome”. Starting with the Prader-Willi syndrome, HHHO is the common name of this syndrome and it is not widely distributed. The clinical symptoms of this disease are numeral but the most important symptom in our study is mental retardation. On the other hand, Angelman syndrome famous by the name of happy puppet syndrome has an effect on 0.003% of the population and it can be diagnosed by certain characteristics such as ataxia and extreme mental retardation (Genetics, 2005, p.2).
Second, monogenic disorders are the result of inactive genes that are incapable to synthesize proteins and enzymes leading to mental disorders (Genetic causes, n.d, p.p1-2) because single gene causes of mental retardation involve mutation in only one gene that will change the functioning of the gene and contribute to subnormal intellectual capacities (Winnepennink et al, 2003, p.29). In this domain it is interesting to note that a small amount of mental retarded people have monogenic disorders (Genetics, 2005, p.2).
In addition, monogenic disorders break down into three categories: The autosomal dominant, the autosomal recessive and the X- linked mental retardation. Actually, the autosomal dominant mental retardation is not widely distributed such as Rubinstein-taybi syndrome which is an example of this disease caused by mutation in the CREB gene situated on 16p13.3 chromosome and stated precisely by many symptoms like a slow development, natural height and many others. Immediately following, autosomal recessive transmission is more frequent than autosomal dominant. In this case the two alleles lost their functions.
An example of autosomal dominant transmission is phenylketonuria involving an error of metabolism from the lack of hydroxylase and the deletions of “four base pairs” in the PRSS12 gene contribute to mental retardation (Winnepenninck et al, 2003, p.29). Next, the X-linked mental retardation results from mutation in the gene on the X chromosome and mostly has an effect on males. 60 out each 100 people with mental retardation and partial of all the X-linked disease present the fragile X syndrome (Martin, 1998, p.22) which result from the inability of FMRI transcription and the absence of its gene. The disorder is characterized by “large ears and elongated face” (Genetics, 2005, p.2). In general a person affected by fragile X syndrome has a low IQ (Martin, 1998, p.9).
Third, chromosomal disorders account for 80% of the genetic disorders of mental retardation (Edgerton, 1979, p 9). These abnormalities occur when there is excess or deficit of chromosomes or change in their construction. For this reason it is not a condition that these genes are inherited. These chromosomal disorders occur during cellular division when chromosomes separate, disperse and recombine leading that the genes of the parents are normal (Genetic causes, n.d, p.p 1-2). The most important chromosomes polyploidy are trisomy 13, 18 and 21 (Winnepenninck et al, 2003, p.29) which are disorders that depend on the increase of the maternal age.In the meanwhile, most of the chromosome disorders are caused by Down syndrome which has a specific region of band 21q21.3-21q22 (Genetics, 2005, p.2) and which affects about 0.0012 of the population.
To end this discussion it is important to note that for the next 10 years, genetic etiology will become one of the most remarkable challenges of simple genetic (Winnepenninck et al, 2003, p.29). After an extended discussion of the genetic causes of mental retardation, It is essential to examine the behavioral causes of this disorder since the general condition of a baby is closely related to the health of the mother (causes of retardation, 2005, p.2). Eventually, many behavioral and physiological states including excessive consumption of substances, blood poisoning and vigorous stress are responsible for abnormal development because these conditions damage the brain and lead to a decrease in its functions (Edgerton, 1979, p.7).
First of all, “substances intake” was a subject to lots of studies because all substances, toxic or not are delivered to the developing embryo by diffusion through the placenta (Kessler, 1965, p.340). Recently, birth imperfection has been joined with the consumption of alcohol but now scientists are sure that alcohol has a serious negative effect on the embryo (Carrol, 2003, p.p 1-3). And according to the “National institute of alcohol abuse and alcoholism”, the risk of mental illness increases and the intelligence quotient falls below the normal when there is an excessive consumption of alcohol (Edgerton, 1979, p.16). In the meantime, a professor, Dr.Sandra w. Jacobson, at Wayne state school of medicine in Detroit, declares that alcohol may affect people in different percentages without a specific rule (Carrol, 2003, p.p 1-3).
In addition to alcohol, cocaine has a lot of negative effects on the newborn including language difficulties and many abnormalities and other serious anomalies (Come-Wesson, 2005, p.2). In comparing alcohol to cocaine, scientists found that alcohol act on several neurotransmitters. From this fact, alcohol attacks several positions in the brain in which make it more harmful. Simultaneously, NAP a protein that stops alcohol alteration of the L1 sticking property (A fibrous band of tissue that binds together normally separate anatomical structures), but when it is damaged by alcohol it will lead to nervous system complications (Carrol, 2003, p.6). Last but not least it is important to note that cigarettes resemble cocaine in its mode of functioning and also act on the brain (Greenfield, 2004, p.p 1-2).