How is mental retardation caused

The management of this problem can include changes in behavior and functional communication training, 77 as well as drug therapy with selective serotonin reuptake inhibitors, trazodone, or buspirone. A recent study has proposed the use of melatonin in the daily dose of 0. Gene therapy of MR secondary to monogenic disorders is still a possible alternative. Abrir menu Brasil. Jornal de Pediatria.

Abrir menu. Rio J. Marcio M. Vasconcelos About the author. Mental retardation; developmental delay; neurogenetics; cerebral plasticity. Key words: Mental retardation, developmental delay, neurogenetics, cerebral plasticity. Introduction Mental retardation MR is one of the most commonly observed neuropsychiatric disorders among children and adolescents.

Neurobiology of mental retardation The human genome mapping project and gene knockout studies with laboratory animals allow determining specific intracellular changes in each gene mutation and the correlation of a deficient molecule with the resulting cognitive deficit, thus establishing the cellular bases of cognition.

The epidemiology of mental retardation of unknown cause. Reported biomedical causes and associated medical conditions for mental retardation among year-old children, metropolitan Atlanta, to Dev Med Child Neurol. MRI in children with mental retardation. Pediatr Radiol. Battaglia A, Carey JC. Am J Med Genet. Diagnostic and statistical manual of mental disorders. Rittey CD. Learning difficulties: what the neurologist needs to know.

J Neurol Neurosurg Psychiatry. Practice parameter: evaluation of the child with global developmental delay. Increased risk for developmental disabilities in children who have major birth defects: a population-based study. Xu J, Chen Z. Advances in molecular cytogenetics for the evaluation of mental retardation.

Ramakers GJA. Rho proteins, mental retardation and the cellular basis of cognition. Trends Neurosci. Stevenson RE. Splitting and lumping in the nosology of XLMR. Risk of mental retardation among children born with birth defects. Arch Pediatr Adolesc Med. Animal models of mental retardation: from gene to cognitive function.

Neurosci Biobehav Rev. Kandel ER. Nerve cells and behavior. Principles of Neural Science. New York: McGraw-Hill; Chechlacz M, Gleeson JG. Is mental retardation a defect of synapse structure and function?

Pediatr Neurol. Contributions of dendritic spines and perforated synapses to synaptic plasticity. Brain Res Brain Res Rev. Dendritic anomalies in disorders associated with mental retardation. Cereb Cortex. Johnston MV. Brain plasticity in paediatric neurology. Eur J Paediatr Neurol. The molecular biology of memory storage: a dialogue between genes and synapses.

Nat Genet. Zoghbi HY. Postnatal neurodevelopmental disorders: meeting at the synapse? Jin P, Warren ST.

New insights into fragile X syndrome: from molecules to neurobehaviors. Trends Bioch Sci. Willemsen R, Oostra BA. FMRP detection assay for the diagnosis of the fragile X syndrome.

Transcription of the FMR1 gene in individuals with fragile X syndrome. Fmr1 knockout mice: a model to study fragile X mental retardation. Aylward GP. Cognitive and neuropsychological outcomes: more than IQ scores.

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Aetiological findings and associated factors in children with severe mental retardation. Develop Med Child Neurol. Epilepsy, intelligence, and psychiatric disorders in patients with cerebellar hypoplasia. J Child Neurol. Nordin V, Gillberg C.

Autism spectrum disorders in children with physical or mental disability or both. I: clinical and epidemiological aspects. The discovery of phenylketonuria: the story of a young couple, two retarded children, and a scientist. Etiologic yield of subspecialists' evaluation of young children with global developmental delay. A genetic diagnostic survey in a population of mentally retarded institutionalized patients in the south of Brazil.

Clin Genet. Evaluation of the child with idiopathic mental retardation. It is the type of support typically required for most mildly retarded individuals. At the other end of the spectrum, pervasive support, or life-long, daily support for most adaptive areas, would be required for profoundly retarded individuals. For children, the mental retardation rate is For adults, the rate is 6.

In 42 states, the rate for children is higher than that for adults; in seven states, the rate for adults is higher, and in two states, both rates are similar. The correlation between state-specific rates for children and for adults is 0. Overall, 69 percent of the state-specific variation in prevalence rates for adults is accounted for by median household income, the percentage of total births to teenaged mothers, and the percentage of the population with less than a ninth-grade education.

Low educational attainment was the most important correlate of mental retardation rates among adults. Low IQ scores and limitations in adaptive skills are the hallmarks of mental retardation.

Aggression, self-injury, and mood disorders are sometimes associated with the disability. The severity of the symptoms and the age at which they first appear depend on the cause. Children who are mentally retarded reach developmental milestones significantly later than expected, if at all. If retardation is caused by chromosomal or other genetic disorders, it is often apparent from infancy.

If retardation is caused by childhood illnesses or injuries, learning and adaptive skills that were once easy may suddenly become difficult or impossible to master. In about 35 percent of cases, the cause of mental retardation cannot be found.

Biological and environmental factors that can cause mental retardation include genetics, prenatal illnesses and issues, childhood illnesses and injuries, and environmental factors. About 5 percent of mental retardation is caused by hereditary factors. Mental retardation may be caused by an inherited abnormality of the genes, such as fragile X syndrome. Fragile X, a defect in the chromosome that determines sex, is the most common inherited cause of mental retardation. Single gene defects such as phenylketonuria PKU and other inborn errors of metabolism may also cause mental retardation if they are not found and treated early.

An accident or mutation in genetic development may also cause retardation. Examples of such accidents are development of an extra chromosome 18 trisomy 18 and Down syndrome. Down syndrome is caused by an abnormality in the development of chromosome It is the most common genetic cause of mental retardation.

Fetal alcohol syndrome affects one in children in the United States. It is caused by excessive alcohol intake in the first twelve weeks trimester of pregnancy. Some studies have shown that even moderate alcohol use during pregnancy may cause learning disabilities in children.

Drug abuse and cigarette smoking during pregnancy have also been linked to mental retardation. Maternal infections and illnesses such as glandular disorders, rubella , toxoplasmosis , and cytomegalovirus infection may cause mental retardation. When the mother has high blood pressure hypertension or blood poisoning toxemia , the flow of oxygen to the fetus may be reduced, causing brain damage and mental retardation.

Birth defects that cause physical deformities of the head, brain, and central nervous system frequently cause mental retardation.

Neural tube defect, for example, is a birth defect in which the neural tube that forms the spinal cord does not close completely.

This defect may cause children to develop an accumulation of cerebrospinal fluid on the brain hydrocephalus. By putting pressure on the brain hydrocephalus can cause learning impairment. Hyperthyroidism, whooping cough, chickenpox, measles , and Hib disease a bacterial infection may cause mental retardation if they are not treated adequately.

An infection of the membrane covering the brain meningitis or an inflammation of the brain itself encephalitis cause swelling that in turn may cause brain damage and mental retardation.

Traumatic brain injury caused by a blow or a violent shake to the head may also cause brain damage and mental retardation in children. Ignored or neglected infants who are not provided the mental and physical stimulation required for normal development may suffer irreversible learning impairments.

Children who live in poverty and suffer from malnutrition , unhealthy living conditions, and improper or inadequate medical care are at a higher risk. Exposure to lead can also cause mental retardation. Many children develop lead poisoning by eating the flaking lead-based paint often found in older buildings.

If mental retardation is suspected, a comprehensive physical examination and medical history should be done immediately to discover any organic cause of symptoms. Conditions such as hyperthyroidism and PKU are treatable. If these conditions are discovered early, the progression of retardation can be stopped and, in some cases, partially reversed. If a neurological cause such as brain injury is suspected, the child may be referred to a neurologist or neuropsychologist for testing.

The symptoms of mental retardation are usually evident by a child's first or second year. In the case of Down syndrome, which involves distinctive physical characteristics, a diagnosis can usually be made shortly after birth.

Mentally retarded children lag behind their peers in developmental milestones such as smiling, sitting up, walking, and talking. They often demonstrate lower than normal levels of interest in their environment and responsiveness to others, and they are slower than other children in reacting to visual or auditory stimulation. By the time a child reaches the age of two or three, retardation can be determined using physical and psychological tests.

Testing is important at this age if a child shows signs of possible retardation because alternate causes, such as impaired hearing, may be found and treated. A complete medical, family , social, and educational history is compiled from existing medical and school records if applicable and from interviews with parents.

Children are given intelligence tests to measure their learning abilities and intellectual functioning. For infants, the Bayley Scales of Infant Development may be used to assess motor, language, and problem-solving skills. Interviews with parents or other caregivers are used to assess the child's daily living, muscle control, communication, and social skills. Federal legislation entitles mentally retarded children to free testing and appropriate, individualized education and skills training within the school system from ages three to For children under the age of three, many states have established early intervention programs that assess, recommend, and begin treatment programs.

Many day schools are available to help train retarded children in basic skills such as bathing and feeding themselves. Extracurricular activities and social programs are also important in helping retarded children and adolescents gain self-esteem.

Training in independent living and job skills is often begun in early adulthood. The level of training depends on the degree of retardation. Mildly retarded individuals can often acquire the skills needed to live independently and hold an outside job. Moderate to profoundly retarded individuals usually require supervised community living. Family therapy can help relatives of the mentally retarded develop coping skills.

It can also help parents deal with feelings of guilt or anger. A supportive, warm home environment is essential to help the mentally retarded reach their full potential. However, as of , there is no cure for mental retardation. A promising but controversial treatment for mental retardation involves stem cell research. In the early s scientists are exploring the potential of adult stem cells in treating mental retardation.

They have transplanted bone marrow cells into living embryos in the uteri of animals to approach congenital diseases, birth defects, and mental retardation. Stem cells are primitive cells that are capable of forming diverse types of tissue. Because of this remarkable quality, human stem cells hold huge promise for the development of therapies to regenerate damaged organs and heal people who are suffering from terrible diseases.

Embryonic stem cells are derived from human embryos. Their use is controversial because such stem cells cannot be used in research without destroying the living embryo. Other sources of stem cells are available, however, and can be harvested from umbilical cord blood as well as from fat, bone marrow, and other adult tissue without harm to the donor. An enormous amount of research involving adult stem cells is going on as of in laboratories in the United States.

Individuals with mild to moderate mental retardation are frequently able to achieve some self-sufficiency and to lead happy and fulfilling lives. To reach these goals, they need appropriate and consistent educational, community, social, family, and vocational supports. The outlook is less promising for those with severe to profound retardation. Studies have shown that these individuals have a shortened life expectancy. The diseases that are usually associated with severe retardation may cause the shorter life span.

The laboratory and radiographic assessment of individual children should be based on clinical presentation Table 3. Suspected contiguous gene syndromes e. Pediatr Rev ; This initial sharing of information with parents is an extremely important step and will probably set the stage for the future physician-family-patient relationship. Ample time should be scheduled to discuss the findings and to allow for questions, which will be numerous.

The family should be encouraged to write a list of questions for further communication with the physician. The Individuals with Disabilities Education Act 17 provides for developmental assessment of children older than three years in every school district. For children younger than three, similar infant-toddler assessment and early intervention resources are available, usually through local health departments, school districts or regional assessment centers.

The responsible agency varies in each state. Families will usually welcome such a referral and comprehensive evaluation, especially if the mental retardation is unexplained. Evaluations by a nutritionist and a child psychiatrist may also be appropriate for some patients. The family physician should expect complete information on the findings from this type of team evaluation. The family should expect to be referred back to their local community for ongoing primary care and, in some instances, subspecialty care.

Information about early intervention resources in the local community should be shared with the family, and appropriate support services should be identified. If the child with mental retardation has a head circumference that falls below the 5th percentile microcephaly or above the 95th percentile macrocephaly , a magnetic resonance imaging scan of the brain should be considered. This is usually preferable to computed tomographic scanning because of the enhanced visualization of developmental abnormalities of the cerebral cortex, such as pachygyria, polymicrogyria and schizencephaly.

These disorders reflect an abnormality during the first 25 weeks of gestation in the early migration of the neurons into the normally six-layered cortex. This would include a review of a three-generation pedigree and records of pertinent relatives, evaluation for subtle dysmorphic features and assessment for a pattern to the patient's presenting characteristics. Most mentally retarded patients who visit a genetics office undergo chromosome analysis.

While this testing could be done by the referring physician, there are different levels of test quality, and it is usually best performed by a good cytogenetics laboratory associated with a university hospital or children's hospital.

This allows for ease in interpretation of the results to the patient's family in the event an abnormality is found. DNA testing for fragile X syndrome should be done instead of cytogenetic testing, which can miss up to 7 percent of those who are affected.

Diagnosis may require several periodic visits to a geneticist, because a phenotype may evolve slowly, and new syndromes are constantly being reported. The importance of making a diagnosis in a child with mental retardation cannot be overemphasized.

An accurate diagnosis allows for anticipatory guidance for the patient, recurrence risk information and genetic counseling for the parents, and opportunities for the family to become involved in specific support groups.

An uncertain diagnosis should be conveyed as such; no diagnosis is preferable to an incorrect one. Within a given family, the risk of recurrence of mental retardation in future siblings or other relatives of the patient depends on the specific diagnosis. The recurrence risk for mental retardation cannot be given to the family until a diagnosis has been made, although a general discussion with a geneticist may be of benefit. The family physician is a valuable resource in periodically reviewing the recurrence risk for the family.

Practice guidelines for primary care of children with certain conditions Down syndrome, fragile X syndrome are also available, 19 — 21 as are special somatic growth charts for some syndromes.

There are also guidelines for the management of adults with mental retardation who have been deinstitutionalized. All physicians who care for children with mental retardation or developmental disabilities should remember that these patients quickly outgrow their childhoods.

As they become adolescents and young adults, most of them will need professional intervention to help them become their own advocates in the health care system. Families should be supported as they encourage independent functioning on the part of their adolescent or young-adult son or daughter. Already a member or subscriber? Log in. Interested in AAFP membership? Learn more. Address correspondence to Grace E. Holmes, M. Reprints are not available from the authors.

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