Borderline Intellectual Functioning Overview

Intellectual functioning can affect a person's risk of developing a psychiatric disorder or substance use disorder. If functioning is below that of the general population, yet not low enough to be classified as an intellectual disability, the person may be diagnosed with borderline intellectual functioning—potentially putting them at greater risk of these types of issues.

Here we explore what borderline intellectual functioning is and the criteria for diagnosis. We also discuss the impacts of a borderline intellectual disability on a person's life and how to get help if this type of condition is suspected.

What Is Borderline Intellectual Functioning?

Borderline intellectual functioning refers to intelligence quotient (IQ) scores within the 71 to 84 range on an intelligence test. This is roughly one to two standard deviations below that of the general population.

It is called borderline because it's on the border of the criteria required for the diagnosis of an intellectual disability in the Diagnostic and Statistical Manual of Mental Disorders (DSM). According to the DSM, an intellectual disability exists when a person's IQ score is 70 or below.

Causes of Reduced Intellectual Functioning

Several factors can contribute to the development of an intellectual disability. They include:

• Brain malformation
• Exposure to toxins like mercury or lead
• Genetic disorders, such as Down syndrome or Fragile X syndrome
• Having an illness like meningitis or measles
• Maternal consumption of alcohol or drugs during pregnancy
• Maternal infection during pregnancy or problems at birth
• Traumatic brain injury
  

How Borderline Intellectual Functioning Is Diagnosed

In the DSM-IV, the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders, there was a diagnostic category called "mental retardation." This diagnosis was made largely through standardized IQ tests. In 2013, when the new DSM-5 was released, mental retardation disappeared and in its place was "intellectual development disorder."

Someone with an IQ of 70 or below is considered to have an intellectual disability under this diagnosis. If their IQ is between 71 and 84, they are considered to have borderline intellectual functioning.

While IQ scores play an important role in recognizing intellectual development disorders, other factors are also taken into consideration. According to the American Psychiatric Association, which publishes the DSM, intellectual disability involves issues with functioning in two areas:

• Intellectual functioning: such as learning, problem-solving, and judgment
• Adaptive functioning: activities of daily living, such as communication and independent living
  

Impacts of a Borderline Intellectual Disability

People with borderline intellectual disability have a greater risk of developing mental health issues than someone with an average or above-average level of intelligence. This risk is higher for almost all psychiatric disorders, including personality disorders.

Research also indicates that people with substance use disorder have a higher prevalence of borderline intellectual functioning than that of the general population. While this study doesn't establish cause and effect, it does show a connection.

This research also found that during substance use disorder treatment, people with borderline intellectual functioning typically experience greater psychological distress. This can impact their treatment outcomes.

Getting Help for Borderline Intellectual Functioning

A person with a borderline intellectual disability will likely need someone else's help to advocate for them and to learn important self-care skills. A mental health professional or other healthcare provider can connect them with resources available that can assist with this. State or federal services may also be available.

In the past, because of the weight given to IQ alone, people with scores between 70 and 85 were generally denied access to the services and support available to people with scores below 70. Today, however, there is more of an emphasis on an individual's ability to function and manage daily living skills.

The determination of whether a person will or will not receive services depends upon many factors, some of which include:

• Whether there is another diagnosis. For example, an individual with autism spectrum disorder and an IQ of 75 may have significantly more difficulty with daily life activities than an individual with Down syndrome and the same IQ.
• Where the individual lives. Rules regarding agency services vary from state to state.
• The kind of support available to an individual. This is determined, in part, based on their living situation.
• If the individual has physical challenges that make it difficult for them to perform ordinary life skills. Some genetic disorders can cause both lowered IQs and also poor muscle tone, reduced coordination, and other physical issues.

Contacting one's local Department of Health and Human Services is a good place to start when trying to determine the resources available to people with intellectual disabilities. Healthcare providers, including mental health practitioners, can assist with this as well.