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September/October 2010 Issue

Co-Occurring Mental Illness and Developmental Disabilities
By Maria Quintero, PhD, and Sarah Flick, MD
Social Work Today
Vol. 10 No. 5 P. 6

For most mental health professionals, the term “dual diagnosis” is used to describe people who have a mental illness and a substance use disorder. However, there is another seldom-recognized population also described as dually diagnosed and posing significant challenges for professionals. These individuals have co-occurring intellectual and developmental disabilities (IDD), formerly called mental retardation, and a mental illness. Surprisingly, few professionals are trained in this specialty or are aware of how frequently the two conditions coexist.

The statistics are concerning and reflect the fact that people with IDD are at a significantly higher risk of mental illness. The prevalence is conservatively estimated at 33%, with some sources reporting much higher rates. This populations susceptibility is increased by biological and social factors. As more mental illnesses are understood to be caused or aggravated by biochemical irregularities, an already-damaged brain is at higher risk of biochemical imbalances.

Additionally, people with IDD are often ostracized and have few, if any, social networks of support. Even with mainstream options in public school, children with IDD are often treated differently and excluded from social activities. As young adults, this isolation becomes more pronounced when students graduate without work prospects or established social circles. Social isolation and exclusion with no hope of change, combined with already-existing brain differences, set the stage for mental illness.

If mental illnesses are so common in persons with IDD, why do so few professionals know about this form of dual diagnosis? Unfortunately, standard clinical graduate programs and medical schools do not include dual diagnosis in their training curriculum. When a clinician sees such a case in a practice, there is often a tendency to recognize only the developmental delay and attribute any odd behaviors to that condition. This phenomenon, known as overshadowing, blinds the clinician to the possibility that a mental illness could be the cause of the behaviors for which the person is being referred (Silka & Hauser, 1997).

A complicating factor in this scenario is the limited communication skills of many people with IDD. This limitation makes it difficult or impossible for them to describe their own experiences accurately to the clinician, according to Silka and Hauser. They may simply have no words with which to explain their feelings and what they are perceiving, yet words are the essential tool of a social worker or other mental health clinician trying to understand what is happening in a client’s or patient’s mind.

In addition, the individual’s cognitive limitations produce intellectual distortions that make it difficult for the person to discern if what they’re experiencing is normal. With limited social exposure, the person has a narrower range of normal experiences against which he can compare his own. It may be difficult for the person to discern that what they are hearing or seeing is outside of the bounds of normal experience, note Silka and Hauser.

Finally, people with IDD often increase or decrease already-existing behavior anomalies (e.g., hand flapping, making loud noises, pacing). These baseline exaggerations are routinely mistaken for learned behaviors that are part of the developmental delays and not assessed as possible symptoms of an emerging mental illness, according to Silka and Hauser.

Without specific training in dual diagnosis, clinicians are unaware of the possibility of co-occurring conditions, fail to ask the appropriate clinical questions, and create circumstances in which these individuals are either untreated, undertreated or, more alarmingly, treated with ineffective or inappropriate methods.

ADAPT: A Program Model
In 1995, these concerns led the Mental Health and Mental Retardation Authority (MHMRA) of Harris County, based in Houston, to develop a program for adults with dual diagnoses: the Adult Developmental and Psychiatric Treatment (ADAPT) program. MHMRA of Harris County is the largest of 39 publicly funded community mental health centers in Texas that provide mental health, crisis, and IDD services and supports. The agency serves more than 30,000 residents of Harris County each year, including people with dual diagnoses. MHMRA celebrates the 15-year anniversary of ADAPT program this year.

ADAPT is a day-habilitation treatment for adults with dual diagnoses for intellectual disabilities and mental illness. It helps adults develop coping and self-management skills and access local resources needed to learn, work, and live as contributing members of their communities. Day-habilitation is a structured schedule of therapeutic activities designed to help each participant develop the skills necessary to maintain stable behavior in various community settings.

The daily schedule includes group and individual training while continually reassessing the person’s progress toward individual goals. Treatment interventions are uniquely designed to meet the needs of adults aged 18 and older experiencing behavioral and emotional problems that impede their daily life, work, relationships, or physical wellness. The therapeutic plan of care allows options for continuous treatment and transitional planning based on each individual’s goals and personal growth.

A team of four clinicians, comprised of a psychiatrist, a psychologist, a registered nurse, and a social worker, along with three direct-care specialists, work with program participants. The ADAPT program serves approximately 18 adults daily. Most commonly, clinicians work with adults diagnosed with mood disorders, anxiety disorders, and impulse-control disorders. Other diagnoses represented in the population served at ADAPT include psychotic disorders and posttraumatic stress disorder.

ADAPT program coordinators structure daily activities and events that promote independence and foster creativity. For instance, ADAPT partners with another MHMRA program, The Coffeehouse, each year to host an art show open to the public where participants display paintings, drawings, or poetry. Many of the artists are available at the art show to highlight their unique creations and share information about their artwork with event attendees. This year the artists decided to donate the proceeds of their sales to the Haitian earthquake relief efforts. In years past, proceeds from the art show have gone back to each artist.

 The program has served more than 300 individuals, and its psychiatric hospitalization rate for participants in ADAPT has been reduced by 90% compared with hospitalization rates prior to program participation. These benefits are seen within a length of stay that averages 9.6 months, much longer than a routine inpatient stay yet more clinically effective and ultimately less expensive than repeated, unproductive inpatient hospitalizations.

Over the years, ADAPT has also seen interesting shifts in the population served by the program. In the early years, few people with diagnoses of autism spectrum disorder were referred. More recently, this diagnosis is common among the adults in ADAPT, perhaps reflecting the global increase in identifying this condition.

From a clinical perspective, it’s exciting to see advancements in the understanding of both mental illness and IDD. However, the need for community services and supports—like those provided by social workers—for people with a dual diagnosis is still significant. Programs such as ADAPT offer hope, opportunity, and encouragement to some of the most vulnerable populations mental health professionals serve, and certainly communities across the country would benefit from more programs like it.

— Maria Quintero, PhD, is assistant deputy director of the IDD services division at the Mental Health and Mental Retardation Authority of Harris Country and a member of the ADAPT program management team. Sarah Flick, MD, is the IDD services division medical director.


Silka, V. R., & Hauser, M. J. (1997). Psychiatric assessment of the person with mental retardation. Psychiatric Annals, 27(3).