The prevalence of mental retardation is approximately 1%.¹ Prevalence rates have varied between 1% and 3% depending on the populations sampled, the criteria used, and the sampling methods.

Currently, there are more than 750 known causes of mental retardation; however, in up to 30% of cases no clear etiology is found.²^–⁶ This can be disheartening for patients, parents, families, and caregivers, as they search for an understanding of a condition that will profoundly affect their lives. This aspect of a patient’s history should be addressed at the start of treatment.

The three most common identified causes of mental retardation are Down syndrome, fragile X syndrome, and fetal alcohol syndrome. Facial features of these conditions are provided in Figures 20-1 through 20-3; knowledge of the dysmorphic features associated with clinical syndromes aids in their identification. Down syndrome is the most common genetic cause of mental retardation; it involves trisomy of chromosome 21. Fragile X syndrome is the most common inherited cause of mental retardation with the FMR1 gene located on the X chromosome. Fetal alcohol syndrome, the most common “acquired” cause of mental retardation, has no identified chromosomal abnormality, as it is a toxin-based insult. These three etiologies account for nearly one-third of cases of mental retardation.

Figure 20-1 Image of an individual with Down syndrome.

Figure 20-2 Image of an individual with Fragile X syndrome.

Figure 20-3 Image of an individual with fetal alcohol syndrome.

CO-MORBID PSYCHOPATHOLOGY

Individuals with mental retardation experience the full range of psychopathology, in addition to some unique behavioral conditions.⁷^–⁹ The rates of psychopathology in this population are roughly four times higher than in the general population ^2,⁶; exact determination is difficult as data collection in this area is confounded by methodological issues (including how to obtain an accurate assessment in the absence of self-report and determining how appropriate certain standardized measures might be in this population). In institutional settings up to 10% of individuals with mental retardation also have some form of psychopathology or behavioral disorder.

Although it is generally accepted that the rates of psychopathology are higher in the mentally retarded, there is less agreement as to why this is so. One theory posits that mental retardation is a brain disorder with as yet unidentified damage to cortical and subcortical substrate. This damage confers heightened vulnerability to psychiatric disorders. Another theory holds that individuals with mental retardation are chronically exposed to stressful and confusing environments, but they lack the cognitive capacity to successfully cope with this stress or to resolve affective conflicts. This eventually wears them down and makes them more vulnerable to psychiatric disorders. Still another theory points to the paucity of good psychological care they receive, which leads to inadequate preventive measures and to delays in diagnosis and treatment.

For many years there was an unwillingness on the part of psychiatrists to aggressively treat a difficult-to-diagnose population. This was superimposed on a movement in the field of mental retardation not to “over-pathologize” behavior. Related to this has been the problem of under-diagnosis, based on the concept of diagnostic overshadowing, that is, the attribution of all behavioral disturbances to “being mentally retarded.”¹⁰^–¹² This stance further marginalizes an already vulnerable population. However, in today’s treatment climate one must also be on guard against over-treatment in the form of misguided polypharmacy. What is needed is a thoughtful approach to diagnosis and treatment of both psychiatric and behavioral disorders in a challenging population.

CLINICAL FEATURES AND DIAGNOSIS

Clinical Features

Familiarity with the diagnostic criteria of mental retardation and its clinical manifestations will aid in the assessment of the functional strengths and weaknesses of a patient with mental retardation who presents for diagnosis and treatment. Table 20-1 presents the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) criteria for mental retardation.¹ These criteria have been adopted from work done by the American Association on Mental Retardation (AAMR), now called the American Association on Intellectual and Developmental Disabilities (AAIDD). Key criteria include the following: below-average intellectual function (as defined by standard intelligence quotient [IQ] testing results that are at least 2 standard deviations below the mean [i.e., an IQ ≤ 70]), in conjunction with impairment in 2 out of 11 areas of adaptive function (compared to peers of the same age and culture), and the symptoms must have been present before age 18 (to denote the congenital nature and life-long course of the diagnosis and to differentiate mental retardation from acquired brain injury and other impairments in cognition that can occur later in life).

Table 20-1 DSM-IV Criteria for Mental Retardation

A. Subaverage intellectual function (i.e., an IQ of 70 or below)

B. Concurrent deficits in adaptive function (relative to the person’s age) in at least two areas (e.g., communication, self-care, home living, social/interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety)

C. Onset before age 18 years

Table 20-1 also lists adaptive areas of function that are assessed when one considers a diagnosis of mental retardation. These domains were not empirically tested and no “gold standard” exists in terms of assessment of level of function. Multiple instruments are available to assist in the assessment; their use varies widely from state to state and from agency to agency. In addition, one can see individuals who may have been diagnosed as mentally retarded, but who do not meet strict IQ criteria. IQ testing can have a standard error of measurement of approximately 15 points. Conversely, there are individuals who may have had a diagnosis of mental retardation, but whose functional level and family support system have allowed them to live and work in society without need for services or supervision. Psychiatrists should be cognizant of the general cognitive level of their patients and assess how cognitive ability may affect their clinical presentation, as well as their compliance and response to treatment.

Table 20-2 presents the DSM-IV-TR classification system (based on severity) for mental retardation along with estimates of their approximate prevalence.¹ These categories do not reflect functional capabilities per se but should be used by the psychiatrist to get a better understanding of how an individual with such an IQ might be expected to present. The overwhelming majority of individuals with mental retardation fall in the mild to moderate category and are the ones most likely to present for community treatment. Individuals with severe to profound mental retardation are more commonly seen in institutional settings, but this can vary greatly from state to state and from region to region.

Table 20-2 Classification of Severity and Approximate Percentages of Mental Retardation in the Population

Severity	IQ Range	Percentage of Population
Mild	50-55 to 70	85
Moderate	35-40 to 50-55	10
Severe	20-25 to 35-40	3-4
Profound	Below 20-25	1-2

Diagnosis

Familiarity with the standard evaluation of mental retardation is helpful to ensure that a patient with a diagnosis of mental retardation has had a through workup and that the diagnosis is accurate.^13,¹⁴ In addition, certain syndromes and causes of mental retardation are associated with specific behaviors and psychiatric disorders. Thus, it is often helpful to identify these syndromes to aid in the clinical assessment.¹⁵

A developmental history (of early milestones and academic and adaptive function) is a good place to begin. This involves primarily ancillary sources of information (such as parents or primary caregivers) as patient accounts are often limited. The presence of a developmental disability should not discourage a psychiatrist from directly addressing this issue with the patient and the family, just as one would ask how a physical or medical disability has affected a patient’s life. Most patients with mental retardation know that they are facing unique challenges and are “different” in some way. Addressing this directly with the patient is often appreciated, as it conveys an openness and respect for the patient as an adult. Conversely, if there is a level of uncertainty or an outright denial around the issue, this may provide impor-tant diagnostic information related to the current clinical situation.

Obtaining information from school, vocational placements, or day programs also helps to establish the accuracy of the diagnosis of mental retardation and to assess the current clinical problem. Further corroboration of the diagnosis should be sought by reviewing the most recent evaluations of adaptive function and neuropsychiatric testing. Neuropsychiatric testing solidifies and quantifies one’s understanding of a patient’s cognitive strengths and deficits. The cause of psychopathology can sometimes be elucidated if a patient’s cognitive profile does not match up well with his or her environmental situation.

Patients need thorough medical and neurological evaluations related to the diagnosis of mental retardation and before being given a diagnosis of a psychiatric or behavioral disorder. One should consider correctable causes (including impairments of hearing and vision, a seizure disorder, or a recent head injury) of both cognitive impairment and behavioral disturbance. For example, there is a high rate of thyroid abnormalities in individuals with Down syndrome.

Although there are no laboratory findings that specifically identify mental retardation, there are multiple causes (including metabolic disturbances, toxin exposure, and chromosomal abnormalities) of mental retardation that can be identified via laboratory analysis.¹⁵ If a patient with mental retardation has never had a chromosomal analysis, a genetics consultation is recommended. This can sometimes shed light on a previously unidentified syndrome in an adult patient that may then help to make a psychiatric diagnosis or to inform family members of potential medical issues that require monitoring. In addition, a genetics consultation can educate the psychiatristabout dysmorphic features in a patient with a given syndrome. The psychiatrist can then use this information to help identify other patients in the future. Figure 20-1 through Figure 20-6 identify dysmorphic features seen in individuals with various syndromes associated with mental retardation.

Figure 20-4 Image of an individual with Prader-Willi syndrome.

Figure 20-5 Image of an individual with Williams syndrome.

Figure 20-6 Image of an individual with 22q11 deletion syndrome.

The differential diagnosis for mental retardation includes specific learning disorders, communication disorders, and borderline intellectual function. Physical disabilities must also be considered in the differential. The presence of a physical disability should not be equated with a cognitive deficiency. Pervasive developmental disorders, such as autism, are considered in the differential diagnosis, but comprise a separate diagnostic category. However, approximately 70% to 80% of individuals with a pervasive developmental disorder also have mental retardation, as defined by standardized, more verbally-based testing.

TREATMENT CONSIDERATIONS

OVERVIEW

Once the psychiatrist has determined that the diagnosis of mental retardation is accurate, that the workup is complete, and that there are no underlying medical or neurological issues affecting behavior, the patient should be assessed for behavioral or psychiatric disorders that may impact adaptive function.^16,¹⁷ The psychiatrist should begin with a basic understanding of the patient’s developmental level and how this might affect the expression of psychiatric symptoms. As previously stated, the full range of psychopathology is seen in the mentally-retarded population. In addition there are unique behavioral disorders and pathobehavioral syndromes or behavioral phenotypes to consider.

The next step in the assessment of an individual with mental retardation involves a functional behavioral analysis that seeks to determine if the patient’s behavior is “functional” in nature, that is, whether the behavior serves a purpose for the individual (not always with direct conscious awareness), such that it is reinforced and continues.^16,¹⁷ Examples include self-injury for the communication of pain, discomfort, or dislike; agitation or loud vocalizations to gain attention of staff or parents; or aggression to “get out of doing something” (i.e., escape-avoidance behavior). In each case, the observed behavior is not part of an underlying psychiatric disorder per se, yet it serves a purpose. If so-called functional behavior is suspected, a referral to a behavior analyst should then be initiated before further assessment or treatment.

A functional behavior analysis may lead the patient back to the psychiatrist, as the behavior analyst may suspect that an underlying psychiatric condition may be driving functional behavior. Examples include depression leading to a desire for increased isolation and subsequent antisocial behavior that accomplishes this goal; increased irritability (related to a mood disorder) that makes previously tolerated stimulating environments now intolerable; or the presence of a paranoid delusion that leads to aggressive behavior out of fear of harm.

Behavioral Disorders

Once a behavior appears to lack an obvious functional utility and cannot be related to an underlying medical or psychiatric condition, it falls in the realm of a behavioral disorder. Nonspecific behavioral disorders (such as aggression and self-injury), as well as more specific disorders (such as stereotypy, pica, copraxia, and rumination), occur in the mentally-retarded population.

Aggressive behavior is the main reason for psychiatric consultation and for institutionalization in the mentally-retarded population. Once a thorough assessment has been completed and no clear etiology found, the problem falls into the realm of an impulse-control disorder. Behavioral treatment is usually the first-line treatment. Subsequent psychopharmacological interventions can be attempted if behavioral treatment proves inadequate. Typically, agents used to treat impulsive aggression are tried; these include alpha-agonists, beta-blockers, lithium, other mood stabilizers/antiepileptic drugs, and antipsychotics.^18,¹⁹

Self-injurious behavior (SIB) refers to behavior that potentially or actually causes physical damage to an individual’s body. This should not be confused with self-mutilation or para-suicidal behavior that is more obviously volitional and seen in individuals with personality disorders. SIB in the mentally-retarded population usually manifests as idiosyncratic, repetitive acts that occur in a stereotypic form. Behavioral therapy is the first-line treatment. Subsequent treatment includes use of selective serotonin reuptake inhibitors (SSRIs) (due to the apparent compulsive nature of the behavior) and neuroleptics in severe and refractory cases.^18,¹⁹

Stereotypy, given the repetitive nature of the behavior, is sometimes related to SIB. Stereotypies are invariant, pathological motor behaviors or action sequences without obvious reinforcement. They often cause no real harm or dysfunction, but may be upsetting to caregivers or staff who may believe that they interfere with the patient’s quality of life. These behaviors are often seen in institutionalized adults with severe to profound mental retardation; however, they can also be seen as a normal variant in children without cognitive delay. These behaviors are often seen in circumstances of extreme stimulation or deprivation. First-line treatment for these stereotypies is behavioral. It is up to the patient or to the patient’s guardian (in conjunction with the psychiatrist) to determine whether to engage in more aggressive medication treatments that are based on the level of dysfunction these behaviors represent. SSRIs should be considered for initial psychopharmacological treatment because of the compulsive nature of these behaviors.^10,^11,^18,¹⁹

Pica involves the eating of inedibles (including dirt, paper clips, and cigarette butts). Although usually seen in those with more severe retardation, this behavior also can be seen as a normal variant in regularly-developing children. One must be aware of the potential medical hazards of ingested items; fortunately, major medical sequelae from this behavior are usually rare. Behavioral therapy (such as environmental control with limited access to preferred items and response-blocking) are the mainstays of treatment. There is minimal evidence that psychopharmacological treatments are useful, and dietary supplements have not been shown to be effective.

Copraxia involves rectal digging, feces smearing, and coprophagia. It is a rare disorder usually seen in the profoundly retarded. Once medical issues are ruled out, sensory issues can be assessed by a trained occupational therapist. Application of appropriate substitute materials can sometimes be helpful. Behavioral therapy again is a first-line treatment. Despite treatment, if the behavior persists, a compulsive or psychotic component should be considered.

Rumination refers to repeated acts of vomiting, chewing, and reingestion of the vomitus. It is seen in those with severe to profound mental retardation, and it can be associated with both gastrointestinal pathology and with behavioral issues (e.g., over-feeding). Self-stimulation also must be considered, as this behavior has been seen in cases of severe sensory deprivation. Conversely, over-stimulation (with anxiety) has also been associated with this behavior. Once gastrointestinal issues are ruled out, behavioral therapy is the mainstay of treatment. If behavioral or gastrointestinal interventions are less than successful, treatment of rumination with medication (as if it were a compulsive behavior or an anxiety disorder) could be attempted; however, it should be viewed as an empirical trial.

Traditional Psychiatric Disorders

Presentations in those with mental retardation can vary (given the decreased ability to self-report and actions that often replace words) from classic descriptions of syndromes. Conversely, individuals with mental retardation who can provide self-reports are often motivated to be liked; they will often tell the psychiatrist what they think he or she wishes to hear. Given these limitations, the psychiatrist must rely more on ancillary sources of information; to this end the treater must help the patient, the parents, and the caregivers to structure their reporting in such a way that data are recorded and presented in as objective a way as possible. Too often data are collected unsystematically; this leaves the psychiatrist in the difficult position of gathering information from a limited number of subjective accounts. It then becomes extremely difficult to assess accurately a clinical situation or the efficacy of various interventions. This leads to less than optimal care for the patient, and to liability issues for the psychiatrist (as clinical decisions are based on less than accurate information).

Affective disorders are good examples where objective reporting of symptoms are necessary. Given the limitations of self-reporting for many patients with mental retardation, the psychiatrist should initiate his or her assessment by documentation of observable mood and behavior changes from the patient’s previous baseline. Mood charts kept by parents or by other caregivers are extremely useful in this regard, especially if a cyclical mood disorder is suspected. Sometimes it is only through observation of the long-term course and longitudinal care that a more definitive diagnosis will be possible. In addition, quantifiable measures (such as sleep logs, calorie counts, and weekly weights) of neurovegetative symptoms can aid in diagnosis. If behavioral changes are the primary presenting problem and there are no other clear symptoms or a family history that might clarify a diagnosis of a mood disorder, reliance on prevalence data may be the psychiatrist’s last hope. He or she may need to initiate an empirical treatment for those disorders that are more common (such as depression or anxiety).

Treatment may involve both talking therapies and medication. The type of therapy recommended should be based on the patient’s strengths and developmental level and should be carried out by a therapist who has experience with the developmentally disabled. Therapy options run the gamut from grief work (especially around transitional times in development), to more concrete cognitive-behavioral therapy (CBT) coping strategies, to nonverbal techniques (such as art, music, or play therapy). Use of medications in mentally retarded patients is the same as it is in the general population. However, in this already compromised population, whenever possible more potent anticholinergic medications should be avoided to lessen the risk of cognitive blunting.

Anxiety disorders are common in the mentally retarded, and observable signs and symptoms of anxiety are often more helpful than are self-reports of anxiety. Those anxiety disorders that manifest with more somatically-based symptoms are easier to diagnose, as staff can measure symptoms (such as elevated pulse and blood pressure in panic disorder), whereas chronic worry (in generalized anxiety disorder [GAD]) may be harder to measure. Anxiety rating scales, both verbal and nonverbal, can be very useful.

Anxiety issues around transitions (daily transitions and around life stages) are commonly seen. The possibility of trauma and related posttraumatic stress must always be considered, especially if there is an acute change from baseline. The mentally retarded are a vulnerable population that is frequently exploited. At times, obsessive-compulsive disorder (OCD) is difficult to distinguish from stereotypy. This is due to the difficulty eliciting self-reported ego-dystonic feelings around the behavior in question. Often, however, if a response-blocking intervention is attempted, individuals with OCD may have increased anxiety, whereas individuals with stereotypy do not. Treatment options for anxiety disorders include relaxation training and other behavioral therapy techniques. Sensory integration interventions can be tried under the guidance of a qualified occupational therapist. A variety of approved psychotropics (including benzodiazepines) should be considered for the relief of anxiety.^10,^18,¹⁹

Psychotic disorders, including schizophrenia, have been noted in the mentally retarded since the days of Kraepelin and Bleuler. However, making an accurate diagnosis remains a challenge. Diminished, and at times confabulatory, self-reporting makes it difficult to establish accurate symptoms. In addition, talking to oneself not related to psychosis is observed in many individuals with developmental disabilities, especially those with Down syndrome. Finally, given the spectrum of psychological development seen in the population, some adults may be developmentally closer to preschoolers than to their chronological age. Having an imaginary friend and talking to a stuffed animal would not be considered psychotic behavior in a preschooler, but this behavior may be misinterpreted in an adult with mental retardation when his or her level of psychological development is not taken into consideration. In making a diagnosis of a psychotic disorder, noting an observable change from one’s baseline level of function (e.g., changes in one’s level of organization, activities of daily living [ADLs], and patterns of interaction with peers and staff) is key. At times there can be observable signs of responding to internal stimuli, but these should be witnessed across multiple settings. Particularly bizarre behavior is noteworthy, yet it should be considered relative to the patient’s history and developmental level (with the knowledge of behaviors unique to this population). In addition, knowledge of the onset and longitudinal course of the illness (e.g., schizophrenia being more likely to manifest in younger age ranges) is useful. Obviously, family history also can provide helpful information. Treatment consists of antipsychotics, both atypical and typical. It is not clear if extrapyramidal symptoms are more common in the mentally-retarded population. However, monitoring for the presence of medication-induced movement disorders including akathisia should be done routinely. Target symptoms of psychosis should be clarified as much as possible so that clear outcome measures are available to monitor and assess the efficacy of medication interventions.

Other types of psychiatric disorders occur in the mentally retarded. Substance-related disorders and personality disorders present particular challenges, as they do in the general population. These disorders usually occur in higher-functioning individuals, and their treatment (e.g., 12-step groups and more cognitive-behavioral interventions, such as modified dialectical behavior therapy [DBT] programs) is similar to that in the general population. Treatment for all other diagnostic categories depends on the psychiatrist’s assessment of the patient’s ability to participate in standard-of-care treatment. Adaptation of the standard of care requires experience working with the population and with teams that can individualize treatment as necessary. Target behaviors for treatment should be identified and quantified to the extent possible, so that the psychiatrist can better assess all interventions.

Syndrome-Associated Disorders

Syndrome-associated disorders are specific psychiatric or behavioral disorders (e.g., self-injury and Lesch-Nyhan syndrome or dementia of the Alzheimer’s type and Down syndrome) that appear to have a higher probability of occurring in individuals with a diagnosed syndrome. Patho-behavioral syndromes and behavioral phenotypes are other terms that have been used to conceptualize this phenomenon. Several common syndromes are encountered in clinical practice; their salient features are provided below.

Individuals with Down syndrome (see Figure 20-1) or trisomy 21 have the classic physical features of round face, a flat nasal bridge, and short stature. Their level of mental retardation is variable.²⁰ Depression is a common psychiatric co-morbidity, but perhaps better known is dementia of the Alzheimer’s type.¹⁵ However, symptoms of dementia often occur in the patient’s forties and fifties. Symptomatic treatment for the accompanying behaviors can be helpful, but it is still unclear what role treatment of the underlying dementia plays (e.g., anticholinesterase inhibitors or NMDA receptor antagonists). Standard treatments often seek to preserve autonomous and independent function and to delay institutional placement, issues that may already have been addressed due to the patient’s baseline cognitive function. Thus, the risk/benefit ratio for the treatment of the underlying dementia and the clarity of outcome measures may be less well defined for this population and should be discussed in detail with a guardian or family member.

Individuals with fragile X syndrome (see Figure 20-2) have an abnormality on the long arm of the X chromosome at the q27 site (FMR1 gene). Common physical features include an elongated face, prominent ears, and macro-orchidism. The majority of affected individuals are males, but females can also be affected. Their level of mental retardation varies.²⁰ Of note, a percentage of female carriers can also display cognitive disabilities. The most prominent co-morbidities are attention-deficit/hyperactivity disorder and social anxiety disorder.¹⁵ In addition, autistic features have been noted in a large percentage of individuals with fragile X syndrome, but autism and fragile X syndrome are not co-occurring conditions.

Individuals with the Prader-Willi syndrome (see Figure 20-4) typically have short stature, hypogonadism, and marked obesity with hyperphagia. In approximately 70% of cases the syndrome results from a chromosome 15 deletion. The level of mental retardation can vary.²⁰ Although the patient can have stubbornness, cognitive rigidity, and rage, the most common psychiatric co-morbidity is OCD.¹⁵ The level of insight with regard to the excessiveness of the obsessions or compulsions can vary, but there is often an ego-dystonic aspect and verbalizations for help.

Williams syndrome (see Figure 20-5) results from a deletion on chromosome 7. These individuals have elfin-like faces and a classic starburst (or stellate) pattern of the iris. They can have supravalvular aortic stenosis, as well as renal artery stenosis and hypertension. Their level of mental retardation varies.²⁰ Behaviorally, they can be loquacious communicators, a phenomenon referred to as “cocktail party speech” (often attributable to a higher verbal than performance IQ). This can be deceiving, as individuals with greater verbal skills can appear to have higher functioning than they actually have. Common co-morbidities include anxiety disorders (such as GAD) and depression.¹⁵

Twenty-two q-eleven (22q11) deletion syndrome (including velo-cardio-facial syndrome and DeGeorge syndrome) is an autosomal dominant condition manifested by a medical history of midline malformations (such as cleft palate, velopharyngeal insufficiency, and cardiac malformations [such as a ventricular septal defect]) (Figure 20-6). Patients have small stature, a prominent tubular nose with bulbous tip, and a squared nasal root. There is often a history of speech delay with hypernasal speech. Their level of cognitive impairment varies from learning disabilities and mild intellectual impairment to more severe levels of mental retardation.²⁰ The reason 22q11 deletion syndrome is of interest to psychiatrists is its high co-morbidity with psychosis (prevalence rates of up to 30% have been reported).²¹ It has been proposed as a genetic model for understanding schizophrenia.²¹