# Handbook of Genetic Counseling/Developmental Delay and Mental Retardation

Developmental Delay and Mental Retardation

## Etiology

* Cause unknown in about 50% of cases
** Often multifactorial with genetic and environmental components
** Low birth weight, prematurity, and perinatal complications may be associated - not known if they cause mental retardation or if factor causing these problems also caused MR
* Approximately 2000 known genetic causes
** Chromosomal abnormalities
** Metabolic or endocrine disorders
** Hereditary degenerative disorders
** Hormonal deficiency
** Hereditary syndromes or malformations
* Acquired causes
** Prenatal: infection, irradiation, or exposure to toxins
** Perinatal: prematurity, anoxia, cerebral damage, or infection
** Postnatal: brain injuries, anoxia, poisons, hormonal deficiencies, metabolic dysfunction, postimmunization encephalopathy, sociocultural, kernicterus, epilepsy
* In United States, 1-3% of people meet cognitive and functional criteria

## Clinical Features

* It is a, medical and mental, developmental disorder
* Affects developmental and cognitive abilities
** Substantial limitations in functioning
** IQ scores below 70
*** Mild MR: IQ range 50-55 to 70
*** Moderate MR: IQ range 35-40 to 50-55
*** Severe MR: 20-25 to 35-40
*** Profound MR: Below 20-25
** Majority of individuals with mental retardation have IQ scores of 55-69
*** Able to live independently or with support in group homes
*** Less than 10% of all people with mental retardation have severe to profound impairments
** May have limited ability to develop some adaptive skills
*** Communication
*** Home living
*** Work
*** Self-care
*** Social/interpersonal skills
*** Self-direction
*** Functional academic skills
*** Leisure
*** Health and safety
*** Use of community resources
* Can affect abilities in key developmental areas
** Language development
** Visual and auditory perception and discrimination
** Abstract problem solving
* Onset must occur before age 18

## Management options

* No treatment or cure
* Early intervention services
** Provided by the county in Ohio to children between birth and age 3
** Studies show the earliest experiences in learning sets the pattern for later information processing
** Begins with comprehensive developmental assessment
*** May be performed here by CCDD or by private service
*** Assessment used to develop intervention strategy
* After age 3, school system provides special services
** Develop an Individualized Education Plan (IEP)
** Early education focuses on cognitive development and special services such as speech therapy
** Later education may focus on developing life skills
** Can attend school until age 21
* Adult services
** Handled in Ohio by the Board of MRDD
** Focuses on job training, vocational education
** Community or group homes are available for semi-independent living

## Recurrence Risks

* Can calculate a much more accurate risk if etiology is known
* Other factors to consider:
** Possibility of consanguinity
** Whether one or both parents are affected
** Developmental disabilities may be exacerbated by environmental factors
*** Unsafe or unstimulating home environment
*** Substandard health care
*** Unadequate schooling or lack of services
* Empiric risk figures when parents affected with mental retardation of unknown etiology
** 39.4% if both parents affected
** 7.8% if only father affected
** 19.6% if only mother affected (higher due to prevalence of X-linked inheritance for conditions such as Fragile X)

## Psychosocial Issues

* Provision of adequate services
* Burden of taking care of a child/adolescent/adult with mental retardation
* Impact on siblings and other family members
* Denial, grief, disappointment, or feeling of loss
* Interruption of career goals, family routines, or plans for the future
* Financial and insurance issues

## References

* Milunsky, Aubry. Prevention of Genetic Disease and Mental Retardation. Philadelphia: W.B. Saunders Company (1975).

## Notes

The information in this outline was last updated in 2001.