Mental retardation (MR) is a group of syndromes characterized by incomplete or impaired intellectual development and difficulties in social adaptation caused by biological and psychosocial factors during the developmental stage of an individual (usually before the age of 18). In past decades, they were usually referred to as cerebral underdevelopment, mental retardation, mental infantilism and mental underdevelopment. In the last decade or so, the education sector tends to use mental retardation (feelble-mindedness), while the civil sector uses intellectual disability (mental handicap). These names actually refer to the same group of people.
Disease Overview
Mental retardation is a relatively common clinical phenomenon and is an important cause of disability. According to the World Health Organization (WHO) statistics (1985), the prevalence rate is 5‰ to 25‰ in developed countries and 46‰ in developing countries. The results of the survey of mental retardation in 12 regions of China (1982), the total prevalence rate was 3.33‰, and 5.27‰ in the 7-14 years old group. 1988 epidemiological survey results of children aged 0-14 years old in 8 provinces and cities nationwide: the total prevalence rate of this disorder was 12‰, 7‰ in urban areas and 14.1‰ in rural areas, the prevalence rate of boys was 7.8‰ in urban areas and 14.3‰ in rural areas; the prevalence rate of girls The prevalence rate of girls is 6.2 per thousand in urban areas and 13.9 per thousand in rural areas; mild is the most common, accounting for 60.6%, and moderate, severe and very severe accounts for 39.4%.
The diagnosis of mild cases of this disorder is difficult in early infancy and is often detected only after school when their intellectual activities are significantly behind those of other children. Some mild cases can adapt to society and perform relatively simple tasks in the absence of special events, thus going unrecognized in the general population. This may be one of the reasons why the prevalence of this disorder in preschool is called high in adulthood, but of course, improper care of the severely affected child or the early death of the combined somatic disease is another reason. With the progress of human social civilization and the development of technology, the situation of people with mental retardation has changed a lot compared to the past. Some of them can live independently in the community with special education and training, and can also become useful to the society.
Mental retardation can present as a single clinical sign or can coexist with other physical disorders involving impaired brain development. If the etiology of mental retardation is known, making a diagnosis should be labeled as such to facilitate management.
Etiology of the disease
There are two main causes of mental retardation: biological factors and psychosocial factors.
(I) Biological factors
1. Prenatal factors
(1) Genetic factors: ① Chromosomal aberrations: including changes in the number and structure of chromosomes. Changes in number include polyploidy and aneuploidy, and changes in structure include chromosome breaks, deletions, duplications, inversions and translocations. For example, Down syndrome, fragile X syndrome, Turner syndrome, etc. With the development of molecular biology techniques, the study of genes associated with mental retardation has received much attention in recent years. Currently, more than 20 genes related to X-linked mental retardation (X,1inked mental retardation, XLMR) have been reported, and the JARIDI C (Jumonji, AT-rich, interactive domain 1C) gene is one of them.The JARIDlC gene is one of the highly conserved The JARIDlC gene is a member of the highly conserved ARID family, which encodes a protein involved in a series of biological effects such as chromatin remodeling, cell proliferation and division, individual development, and regulation of gene transcription, and is abundantly expressed in the brain, thus playing an important role in the normal development and maintenance of normal function of the nervous system. It has been found that small mutations within this gene such as insertions, deletions, and translocations can cause mental retardation, thus becoming one of the current hot spots for research on mental retardation and human cognitive ability related genes. (ii) Monogenic genetic disorders: such as phenylketonuria, tuberous sclerosis, neurofibromatosis, galactosemia, familial microcephaly, etc., which often cause mental deficits. (iii) Polygenic diseases: Polygenic diseases are the result of multiple genes acting together. Although each gene acts individually and minimally, there is a cumulative effect, which, together with the influence of environmental factors, determines the susceptibility of an individual to a trait or disease. If the susceptibility is high and exceeds the threshold for the disease, it will lead to the disease. Common polygenic genetic disorders with mental retardation are: neural tube malformations, mental retardation without clinical symptoms, i.e. familial mild mental retardation without meditative organic features.
(2) Maternal exposure to harmful factors during pregnancy: ① viral and toxoplasma infections: among viral infections, rubella virus, herpes simplex virus, cytomegalovirus have the greatest impact on the fetus, and if the infection occurs in the first trimester after pregnancy, the damage is more severe. ②Drugs and chemical toxins: such as salicylates, diazepam, Librium, phenytoin sodium, progesterone, and lead, mercury, alcohol, etc. ③Radiation. ④Maternal health condition: mother suffering from serious physical diseases during pregnancy, such as hypertension, heart disease, diabetes, severe anemia, severe malnutrition, iodine deficiency, etc. may affect fetal development and lead to mental retardation. The mother’s gestational age is more than 40 years old, which may lead to chromosomal aberrations. ⑤ Insufficient placental function. (6) Emotional factors: long-term anxiety, depression or acute trauma during pregnancy may adversely affect the development of the fetal central nervous system.
2.Partum factors
Intrauterine distress, birth asphyxia, birth injury resulting in cranio-cerebral injury and intracranial hemorrhage, nuclear jaundice, etc. may lead to fetal and neonatal central nervous system damage, resulting in mental retardation. Premature infants, very low birth weight children are often affected by the development of the central nervous system, which may appear behind the intellectual development.
3.Postnatal factors
Central nervous system infection, severe cranial trauma, various causes of cerebral hypoxia, metabolic or toxic encephalopathy, severe malnutrition, hypothyroidism, heavy metal or chemical poisoning, premature closure of cranial suture, etc. may lead to mental retardation. For example, lead is the most prevalent neurotoxin in the environment, and studies have shown that there is a significant association between blood lead levels and cognitive deficits in childhood, but excessive blood lead cannot be easily taken as the main cause of mental retardation.
(ii) Psychosocial factors
Severe isolation from society in early childhood due to poverty or neglect or abuse, lack of benign environmental stimulation, and lack of cultural and educational opportunities can all lead to mental retardation.
Clinical manifestations
The main clinical manifestations of mental retardation are mental retardation and social adjustment difficulties. Intelligence, also known as intelligence, mainly includes the knowledge and experience acquired in the past and the ability to use them to solve new problems and form new concepts, which is formed gradually through various forms of learning and social practice activities in the real society on the basis of innate qualities. The level of intelligence is reflected by the intelligence quotient (IQ), which is (IQ age/actual age) × 100 and can be assessed by various methods. Social adaptability is the ability to adapt to the requirements of daily life, work, family and society, including: daily living skills, independent living and self-sufficiency, social interaction skills and responsibility, etc., which can be evaluated by the social adaptability scale.
Depending on the level of intelligence, mental retardation is classified into four levels: mild, moderate, severe and very severe, and the clinical manifestations of each level are as follows.
(A) Mild
About 75-80% of this disorder, IQ range is 50-69, the adult intelligence level is equivalent to 9-12 years old normal children. The symptoms are not prominent in the infancy and early childhood, but the speech and walking are slightly delayed than normal children, so it is not easy to be recognized. After going to school, the child can learn to read, write and calculate skills, but because the child’s memory, comprehension and abstract generalization ability are poor, the learning difficulties are often obvious, and after the third grade, the child has difficulty in passing various subjects and cannot complete ordinary elementary school. The child’s speech is not significantly impaired. In adolescence, children can learn general personal life skills, take care of themselves, have good independence, and learn general household chores. In adulthood, they can learn simple manual operations, most of them can live independently, and they can also establish friendships and families. However, because of their poor ability to cope with difficulties and their tendency to react in a reactive state when encountering adverse stimuli, they often need intensive support and guidance. Children with this degree generally do not have abnormal neurological signs and somatic deformities, and less than half of them have an identifiable biological cause.
(ii) Moderate
About 12% of children with this disorder have an IQ range of 35-49, and their adult intelligence level is equivalent to that of normal children aged 6-9 years. The child’s speech and motor development in infancy and early childhood is significantly lagging behind that of normal children of the same age, and the level of speech development is limited. Although they have some learning ability, some of them can learn to read, write or calculate in a very simple way after long-term education and training, but it is difficult for them to adapt to ordinary elementary school life and reach the academic level of the first and second grade of elementary school. The children have poor social adaptation ability and show difficulties in personal life skills at an early age, such as the development of hygiene habits and the ability to dress and eat. In adulthood, they cannot live independently, but they can learn to take care of themselves and perform simple manual tasks under supervision. Most of the children in this category are caused by biological factors, and some of them have abnormal neurological signs and somatic deformities.
(C) Severe
About 8% of the children with this disorder have an IQ range of 20-34, and their intelligence level in adulthood is equivalent to that of 3-6 normal children. The development of speech and movement in infancy and early childhood is more delayed than that of children with moderate disorders, and speech and walking are very late. Speech is more severely impaired, and the child can only learn simple words and phrases and has a poor vocabulary. The child’s memory, comprehension, and abstract generalization skills are extremely poor, making it difficult for the child to establish the concept of number, to receive learning education, and to identify and avoid danger. Emotional infantilism. Although they can learn some simple self-care skills, such as feeding themselves and simple hygiene habits, through repeated training over a long period of time, they cannot take care of themselves in adulthood and need care throughout their lives. This group of children is often caused by significant biological factors and is often associated with neurological dysfunction and somatic deformities.
(iv) Very severe
About 1-5% of the children with this disorder have an IQ range of less than 20 and an adult IQ level lower than that of a normal 3-year-old child. These children have very poor development, walk very late, and some of them cannot walk for the rest of their lives; they have no language or occasionally speak simple words. Memory and comprehension are even worse than in severe cases, and they cannot distinguish between close and distant relatives, do not know how to avoid danger, and have primitive emotional responses, only screaming or shouting to express emotions and demands. They have very poor social adjustment skills and have difficulty benefiting from educational training. They lack the ability to take care of themselves and require lifelong care. These children are almost always caused by significant biological factors, and often have significant neurological dysfunction and somatic deformities. Most children die at an early age due to severe physical illness.
In addition to the above, children with mental retardation often have hearing impairment, visual impairment, motor impairment, urinary and fecal incontinence, and epilepsy. Some children have somatoform deformities and specific physical characteristics. Other psychiatric disorders, which are more prevalent than in the general population, may also occur, including behavior disorders, phobias, obsessive-compulsive disorder, generalized anxiety disorder, childhood autism, schizophrenia, affective disorders, and organic mental disorders.
Differential diagnosis
1, attention deficit and hyperactivity disorder Because of inattention affecting learning and social adaptation, it appears to be mental retardation, but the developmental delay is not obvious in the medical history of these children, there are typical symptoms of attention deficit and hyperactivity disorder, the intelligence examination results are normal or borderline intelligence level, after improving attention and reducing hyperactivity, learning difficulties often improve to varying degrees.
2. Childhood autism Childhood autism is often accompanied by mental retardation. If the child meets the diagnostic criteria of both mental retardation and childhood autism, both diagnoses need to be made. For children with high-functioning autism with normal intellectual development, they are also easily misdiagnosed as mental retardation because of their poor social adaptation ability. At this time, the results of intelligence tests can help in the differential diagnosis.
Diagnostic steps
1. Collect detailed medical history. Collect the child’s maternal and perinatal conditions, personal growth and development history, parenting history, past illness history, and family cultural and economic status to find out whether there are any factors that are unfavorable to the child’s physical and psychological development.
2. Comprehensive physical examination and relevant laboratory tests. They include: growth index examination (such as height, weight, head circumference, skin palm prints, etc.), relevant endocrine and metabolic examinations, EEG, EEG topography, head X-ray, CT and MRI examinations, chromosome analysis and fragile loci examination.
3.Psychological development assessment
(1) Intelligence test: It is one of the main bases for the diagnosis of mental retardation. Intelligence tests should be used judiciously by trained and specialized technicians. It should not be used as a group or screening method when used for diagnosis, but should be used as an individual test with diagnostic scales. At present, the commonly used scales in China include: Gesell Developmental Diagnostic Scale, Wechsler Preschool Scale of Intelligence (WPPSI), Wechsler Scale of Intelligence for School-aged Children Revised (WISC-R), Chinese Binay Test Scale, etc.
(2) Assessment of socially adaptive behavior: The judgment of socially adaptive behavior is another important basis for the diagnosis of mental retardation. At present, for children aged 4-12 years, the Social Adaptive Ability Scale (compiled by Yao Shuqiao et al.) can be used to assess the social adaptive ability of the child. If it is not suitable for use, people of the same age and cultural background can also be used as a benchmark to determine the degree of independent living ability that the examined person can achieve and perform his or her social functions. Reference can also be made to the use of the Infant – Junior Adaptive Behavior Scale (revised by Q. Zuo et al.), the AAMD Adaptive Behavior Scale developed by the American Association on Mental Retardation, and the Vineland adaptive behavior scale (Vineland adaptive behavior scale).
(3) Clinical developmental assessment: In clinical work or when intelligence testing is not available, clinical developmental assessment can be used, i.e., the developmental level of the child can be assessed according to the clinical manifestations of mental retardation and developmental characteristics at all levels, and a more correct assessment may also be obtained. [1-3]
Disease treatment
The etiology of mental retardation is diverse, and many causes are still unknown, making treatment difficult. However, due to the development of biomedicine, genetics and rehabilitation medicine, the adoption of comprehensive prevention and treatment measures and the improvement of the social environment, most people with mental retardation have been transformed from a burden to a productive force in society, changing the tendency to underestimate their developmental potential and the pessimistic attitude.
The principles of treatment for this disease are early detection, early diagnosis, and early intervention, and comprehensive measures such as educational training and pharmacological treatment should be used to promote the development of the child’s intellectual and social adaptation abilities. In addition, studies have shown that MR children are a serious negative life event for families, with a long recovery period and poor prognosis, and are prone to long-term psychological stress and psychological burden for mothers of children with MR; rehabilitation training for MR children requires greater energy, physical strength, and time from mothers; rehabilitation treatment and care for MR children affect the family’s economic income and the mother’s own career development; the gap between MR children and normal children and social prejudice and even discrimination against The gap between MR children and normal children and the social prejudice and even discrimination against the children; all of these can cause great life, economic and psychological pressure to the mothers. Therefore, we should also pay attention to the psychological health of mothers with MR.
1. Etiological treatment
Only a few causes of mental retardation can be treated etiologically, such as phenylketonuria, galactosemia, and congenital hypothyroidism. If the above diseases can be diagnosed and treated early, the damage to the child’s intelligence can be prevented or reduced.
2. Symptomatic treatment
For children with mental retardation with various mental disorders, such as hyperactivity, attention disorders, behavioral abnormalities, mood disorders, etc., or children with physical diseases such as epilepsy, corresponding psychotropic drugs are available for treatment. In addition, a variety of drugs that promote and improve the function of brain cells can be used to promote the intellectual development of patients, such as piracetam, cerebral aminopeptide, aminolevulinic acid and some educational Chinese medicines. These drugs can improve the activity of some enzymes in the brain and promote the metabolism of glucose and amino acids in the brain, thus playing a therapeutic role. For children with sensory and motor disorders, rehabilitation training should be strengthened to promote the recovery of their functions.