Mental Retardation

According to the text revision of the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), a diagnosis of mental retardation can be made only when both the intelligence quotient (IQ) as measured by a standardized test, is subaverage and a measure of adaptive function reveals deficits in at least two of the areas of adaptive function. Mental retardation diagnoses are coded on Axis II in the DSM-IV-TR.

Approximately 85 percent of persons who are mentally retarded fall within the mild mental retardation category (IQ between 50 and 70). The adaptive functions of mildly retarded persons are affected in several areas, such as communications, self-care, social skills, work, leisure, and safety. Mental retardation is influenced by genetic, environmental, and psychosocial factors, and in past years, the development of mild retardation was often attributed to severe psychosocial deprivation. More recently, however, researchers have increasingly recognized the contribution of a host of subtle biological factors, including chromosomal abnormalities; subclinical lead intoxication; and prenatal exposure to drugs, alcohol, and other toxins. Furthermore, evidence is increasing that subgroups of persons who are mentally retarded, such as those with fragile X syndrome, Down syndrome, and Prader-Willi syndrome, have characteristic patterns of social, linguistic, and cognitive development and typical behavioral manifestations.

Students should study the questions and answers below for a useful review of this topic.

Helpful Hints

Students should define these terms.

adaptive functioning
Bayley Infant Scale of Development
borderline intellectual functioning
Cattell Infant Scale
causative factors
chromosomal abnormality
cri-du-chat syndrome
CVS (chorionic villi sampling) and amniocentesis
degrees of mental retardation (mild, moderate, severe, profound)
Down syndrome
fetal alcohol syndrome
fragile X syndrome
intelligence quotient (IQ)
Lesch-Nyhan syndrome
mental deficiency
mental retardation
neurofibrillary tangles
neurofibromatosis
PKU
Prader-Willi syndrome
prenatal exposure
primary, secondary, and tertiary prevention
rubella
Special Olympics
Turner’s syndrome
Vineland Adaptive Behavior Scales
WHO

Questions

Directions

Each of the questions or incomplete statements below is followed by five suggested responses or completions. Select the one that is best in each case.

37.1 Which of the following is not a text revision of the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) criterion for mental retardation?

A. Onset before the age of 18 years

B. Severe verbal learning delays

C. An IQ of approximately 70 or below

D. Concurrent deficits or impairment in social or interpersonal skills

E. All of the above

View Answer

37.1 The answer is B

Severe verbal learning delays are not listed as one of the criteria for identifying mental retardation. According to the DSM-IV-TR, there are three criteria for diagnosing mental retardation. First, onset of the disorder must occur before the age of 18 years. Second, in order to make a diagnosis of mental retardation, the patient’s IQ must be significantly below average (IQ of 70 or below). Finally, the patient must have concurrent impairments in adaptive functioning (meeting the standards of the individual’s particular age or cultural group) in two or more of the following areas: social and interpersonal skills, the ability to care for oneself, functional academic skills, work, health, leisure, and safety.

37.2 Profound mental retardation is defined as

A. an IQ of 70 or below

B. an IQ between 40 and 55

C. an IQ of 25 or below

D. an IQ of 25 to 40

E. an IQ of 55 to 70

View Answer

37.2 The answer is C

Profound mental retardation involves an IQ of 25 or below. The condition affects only 1 to 2 percent of people with mental retardation and involves pervasive deficits in all areas of functioning. An IQ ranging between 55 and 70 is classified as mild mental retardation. This is the largest group of people with mental retardation, encompassing as many as 85 percent of all mentally retarded people. An IQ between 40 and 55 indicates moderate mental retardation. About 10 percent of all mentally retarded people fall into this category. Most individuals with moderate mental retardation also have impaired cognitive functioning. An IQ of 25 to 40 indicates severe mental retardation. Between 3 and 4 percent of all mentally retarded people are severely impaired. These individuals also have concurrent motor, ambulatory, and neurological problems.

37.3 A decline in IQ begins at approximately 10 to 15 years in which of the following disorders?

A. Down syndrome

B. Fragile X syndrome

C. Cerebral palsy

D. Nonspecific mental retardation

E. Fetal alcohol syndrome

View Answer

37.3 The answer is B

Children with Down syndrome show their highest IQ scores during the first year of life and then decline in IQ over the early to middle childhood years. Boys with fragile X syndrome also decline in IQ, but their declines seem to begin at approximately 10 to 15 years of age. Conversely, children with cerebral palsy (half of whom have mental retardation) remain remarkably stable in their IQ scores over time, similar to groups with mixed or nonspecific etiologies of mental retardation.

37.4 Which of the following disorders is least often associated with fragile X syndrome?

A. Autistic disorder

B. Schizotypal personality disorder

C. Attention-deficit/hyperactivity disorder

D. Bipolar disorder

E. Social anxiety disorder

View Answer

37.4 The answer is D

Fragile X syndrome is associated with shyness, gaze aversion, and social difficulties. A number of psychiatric diagnoses commonly co-occur with fragile X, including autistic disorder, schizotypal personality disorder, attention-deficit/hyperactivity disorder, and social anxiety disorder. These difficulties vary in severity in this population and are found in individuals with fragile X syndrome across the IQ spectrum, from those with moderate mental retardation to those with mild learning disabilities. Bipolar disorder is less commonly associated with fragile X syndrome than these other disorders.

37.5 Among all known causes of mental retardation, which of the following syndromes is least associated with comorbid Axis I psychiatric disorder?

A. Down syndrome

B. Fragile X syndrome

C. Nonspecific type

D. Fetal alcohol syndrome

E. Prader-Willi syndrome

View Answer

37.5 The answer is A

Compared with other individuals with mental retardation, persons with Down syndrome appear to suffer less often and less severely from psychopathology. Rates of psychiatric disorders in children and adolescents with Down syndrome exceed those in the general population but are significantly lower than in persons with mental retardation caused by other etiologies, such as fragile X syndrome, fetal alcohol syndrome, Prader-Willi syndrome, and nonspecific type. Commonly noted psychiatric problems among individuals with mental retardation include attention problems, impulsivity, hyperactivity, and aggression. In contrast to these problems, depression seems to be less common in persons with mental retardation than in the general population.

37.6 A microdeletion on chromosome 7 is the primary cause of

A. Prader-Willi syndrome

B. fragile X syndrome

C. Williams’ syndrome

D. Rett syndrome

E. none of the above

View Answer

37.6 The answer is C

Williams’ syndrome is caused by a microdeletion of the gene responsible for the body’s production of elastin, a protein that provides strength and elasticity to vital tissues of the body (e.g., blood vessels and lungs). This gene is located on chromosome 7. Persons with Williams’ syndrome often show hyperacusis, hypercalcemia, neuromusculoskeletal and renal abnormalities, and cardiovascular disease (especially supravalvular aoritic stenosis). Characteristic facial features are described as elfin-like, cute and appealing.

Prader-Willi syndrome is the only known human disease that is affected by genomic imprinting, in which genes are modified and expressed differently depending on whether the mutation, which occurs on chromosome 15, is inherited from the mother or the father.

Fragile X syndrome is the most common inherited form of mental retardation. Fragile X syndrome occurs when the fmr1p (or fragile X gene) becomes methylated as a result of amplification (repetition) of the trinucleotide sequences (CGG) that make up DNA.

Rett syndrome is caused by mutations in the gene MECP2 located on the X chromosome and can arise (1) sporadically or (2) from germline mutations. Rett syndrome is exclusively a female disorder because male fetuses with this syndrome rarely survive to term, and those who do die shortly after birth. Males cannot survive with Rett syndrome because they lack the second X chromosome, which in females compensates for the damage to the other X chromosome.

37.7 All of the following chromosomal aberrations associated with Down syndrome lead to a phenotypic expression of the disorder except

A. patients have 45 chromosomes

B. patients have three copies of chromosome 21

C. patients have 47 chromosomes

D. patients have 46 chromosomes, but two, usually 15 and 21, are fused

E. patients have mosaicism, with normal and trisomic cells in various tissues

View Answer

37.7 The answer is A

Three types of chromosomal aberrations are recognized in Down syndrome. First, patients with trisomy 21 (three copies of chromosome 21 rather than the usual two) represent the overwhelming majority of individuals with Down syndrome. They have 47 chromosomes with an extra copy of 21. The mother’s karyotypes are normal. A nondisjunction during meiosis is responsible for the trisomy.

Second, nondisjunction occurring after fertilization in any cell division results in mosaicism, with both normal and trisomic cells found in various tissues.

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