1. Answer: B. Mental retardation is characterized by (1) significantly below-average intellectual functioning with an IQ of 70 or below, (2) onset before 18 years of age, and (3) significant limitations in adaptive functioning in at least two of the following skill areas: communication, self-care, home living, social interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety. Mental illness may or may not be present.

2. Answer: C. Moderate mental retardation accounts for about 10% of the total mental retardation population. Most individuals with this level of mental retardation acquire communication skills during early childhood years and benefit from vocational training. During adolescence, their difficulties in recognizing social conventions may interfere with peer relationships. In their adult years, the majority are able to perform unskilled or semiskilled work under supervision in shelter workshops or in the general workforce. They have the approximate mental age of a 9-year-old child.

3. Answer: A. Mild mental retardation is characterized by an IQ of 55 to 70. These individuals account for about 85% of the population with mental retardation. They typically develop social and communication skills during preschool years, have minimal impairment in sensorimotor areas, and are often not distinguishable from children without mental retardation until a later age. By their late teens, they can acquire academic skills up to approximately the sixth grade level. During their adult years, they usually achieve social and vocational skills adequate for self-support. Some may need supervision, guidance, and assistance, however, especially when under unusual social or economic stress. With appropriate support, individuals with mild mental retardation can usually live successfully in the community either independently or in supervised settings.

4. Answer: E. Mental retardation is associated with various other physical and mental health problems. All of the conditions mentioned are seen more often in individuals with mental retardation. Psychiatric conditions such as ADHD, anxiety disorders, and psychosis are also more common in individuals with mental retardation than in the general population.

5. Answer: C. The prevalence of seizure disorder in individuals with mental retardation varies with the severity of mental retardation. Those with mild mental retardation have a prevalence of 15% to 20%, whereas those with severe mental retardation have a prevalence of 30% to 50%.

6. Answer: B. Down’s syndrome is the most common cause of mental retardation in the general population. The risk of Down’s syndrome increases with increasing maternal age. Fragile X syndrome is the most common inherited cause of mental retardation.

7. Answer: A. Fragile X syndrome is the most common inherited cause of mental retardation.

8. Answer: C. Down’s syndrome is characterized by short stature, brachycephaly, epicanthic folds, Brushfield spots, single palmar crease, high arched palate, protruded tongue, syndactyly, short hands, and atlantoaxial instability. These individuals often develop dementia in their early 40s.

9. Answer: E. Fragile X syndrome accounts for half of all the X-linked mental retardation cases. The genetic abnormalities are caused by an abnormal trinucleotide CGG repeat at a fragile site on the X chromosome. People with Fragile X syndrome have a short stature, macro-orchidism, large head, high arched palate, hyperextensible joints, flat feet, inguinal and hiatal hernia, enlarged aortic root, and mitral valve prolapse. Seizures may be seen in up to 25% of individuals. Cat-like cry is a feature of cri-du-chat syndrome caused by deletion of the short arm on chromosome 5.

10. Answer: C. The main features of Prader-Willi syndrome are hypotonia, hypogonadism, hypomentia, and obesity. The majority of these individuals have mild-to-moderate mental retardation and develop hyperphagia between the age of 1 and 4 years. They also have small hands and feet, cleft palate, incurved foot, congenital hip dislocation, scoliosis, heart disease, and deafness. Hypersexual behavior is not a feature of Prader-Willi syndrome.

11. Answer: D. Rett syndrome is exclusively seen in females. After 1 to 2 years of age, a normally developing child begins to slow or regress and develops unusual characteristic hand movements. Loss of developmental skill occurs, and head growth decelerates. As individuals with Rett syndrome approach adolescence, they develop increased spasticity, scoliosis, bruxism, hyperventilation, sleep apnea, and seizures.