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