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Chapter 12
Mental Retardation
• Mental retardation recognized perhaps
longer than any other currently studied in
• Written documents from ancient Egypt
made oblique reference to the condition as
early as about 1500 BC
– was often viewed as part of mental illness
• relatively common
Defining Mental Retardation
4 assumptions outlined by AAMR
• Valid Assessment considers cultural and linguistic
• Existence of limitations in adaptive skills occurs
in context of community environments
• Specific adaptive limitations can coexist with
• With appropriate support, life functioning will
generally improve
• Communication, the ability to understand
and communicate information
• Self-care skills such as toileting, eating,
• Home living, including interchange wit
• Social skills, including interchange with
• Community Use, including shopping and
obtaining services and use of community
• Self-direction, such as making choices and
following a schedule
• Health and safety, including eating and
basic first aid
• Functional academics, skills related to
learning in school that have direct
application in life
• Leisure, developing a variety of leisure and
recreational interests
• Work, the ability to maintain part- or fulltime employment
Defining Mental Retardation
• American Association on Mental Retardation
– Mental retardation refers to substantial limitations in
present functioning. It is characterized by significantly
sub average intellectual functioning, existing
concurrently with related limitations in two or more of
the following applicable adaptive skill areas:
communication, self-care, home living, social skills,
community use, self-direction, health and safety,
functional academics, leisure, and work.
• Definition departs from earlier efforts in several
• One important difference involves the manner of
viewing intelligence measures
• The AAMR definition focuses on intellectual
functioning primarily at the time of diagnosis and
mainly considers an individual’s adaptive skills
and needed environmental supports for
classification and program planning
Adaptive behavior
• Part of the conceptualization of mental
retardation for over 35 years
Describing and Classifying Mental
• 5 DSM-IV-TR severity classifications for
mental retardation
Mild – IQ of 50-55 to about 70
Moderate – IQ of 35-40 to 50-55
Severe – IQ of 20-25 to 35-40
Profound – IQ below 20 or 25
• Unspecified – presumption of mental
retardation but intelligence not testable with
standardized instruments
• The term mental retardation extremely general
label that covers a heterogeneous set of conditions
with different developmental paths and causes
• Historically, the characteristic most typically
associated with mental retardation has been
reduced intellectual functioning
• The severity of the intellectual impairment has
long been a common means of describing and
classifying those with retardation
• General estimates of prevalence for mental
– Ranged from 1% to 3% of general population
– About 11% of all children with disabilities in
US public schools, and what does this mean in
terms of numbers of individuals receiving
services under IDEA?
Developmental Factors Explain how development plays a role
in mental retardation
• Pregnancy: unborn baby develops rapidly
and is vulnerable to diseases, maternal
nutritional status, and accidents
– Rubella
• Infancy/Early childhood: dependent on
his/her environment for nutrition, oxygen,
protection from disease and trauma
• Metabolic Disorders: Child susceptible in
prenatal and early childhood
• The causes of mental retardation are many
and varied
• In some cases, pathology of a physiological
or biological nature can be identified
• for as many as 30–40% of those with
mental retardation, causation is unknown
Prenatal and Neonatal Causation
• Factors that may cause mental retardation during
the prenatal and neonatal periods
– Genetic Factors
– Maternal Characteristics
– Clinical defects
– Birth problems due to delivery positions or atypical
labor periods
– Low birth weight and inadequate gestational age
Genetic Factors
• Down syndrome
– three types of Down syndrome, each resulting
from a different type of chromosomal error.
• Nondisjunction
• Translocation
• Mosaicism
Genetic Factors
• Fragile X syndrome
– name derives from the fact that the X chromosome of
an affected individual will show a fragile spot when
grown in an experimental culture
• phenylketonuria (PKU), an inherited metabolic
disorder that occurs in about 1 of every 10,000
live births
– Affected infants lack the ability to process
phenylalanine, severely damages the central nervous
Genetic Factors
• Maple syrup urine disease
– Affected infants tend to excrete urine that has a
distinctive odor of maple syrup
– may cause severe intellectual impairment, although
more often than not the condition is fatal
– cause of this condition has been linked to metabolic
deficiencies of three separate amino acids causing
extreme CNS damage in the newborn
• Untreated maple syrup urine disease is fatal; few
untreated infants survive more than a few weeks
Genetic Factors
• Galactosemia involves difficulty in
carbohydrate (sugar) metabolism, rather
than amino acid metabolism
• Infants with galactosemia are unable to
properly process certain sugar components
in milk
• Results are toxic damage to the infant’s
liver, brain, and other tissues
• Not all genetic disorders are metabolic in
• Some sex-related (occurs in the sex
chromosome portion of the genetic
• Other genetic disorders may produce a
variety of physical and functional
Maternal Characteristics
• Maternal age
• adequate nutrition may be one of the most
important factors
• Such problems become especially severe when
expectant mothers do not have access to health
care advice or to prenatal medical care
• However, the specific relationship remains unclear
• Sometimes the unborn fetus inadequately
nourished regardless of the mother’s nutritional
• Thyroid deficiency, chronic diabetes, and
anemia may substantially affect the
development of the fetus and result in
premature birth
• Prematurity substantially increases the
possibility of intellectual impairment
• Maternal diabetes is always considered to
create some degree of risk for the baby
• Serious damage to the fetus may be caused if
mother and fetus have incompatible blood types.
(Rh factor)
• A variety of maternal infections
• German measles (rubella) is perhaps the viral
infection most widely recognized as causing
mental retardation.
• Syphilis
• Toxoplasmosis
• Chemicals, drugs, alcohol, and smoking
– a possible consequence of maternal alcohol
abuse during pregnancy is fetal alcohol
syndrome (FAS) or the less severe fetal alcohol
effects (FAE)
Clinical Defects
• Anencephaly occurs early and results in
incomplete development of the forebrain portion
of cerebral tissue
• Improper closure at other parts of the neural tube
may also cause damage to the central nervous
system in the form of a condition known as spina
• Hydrocephalus is a clinical defect that is
sometimes related to improper closure of the
neural tube
Atypical Birth
• Birth is stressful to mother and infant alike
• current thinking focuses much more narrowly on
the physical trauma of atypical births
– The position of the fetus in utero
• Other fetal positions substantially raise the
probability of damage
– breech presentation Several difficulties may result from
a breech birth
• may place a great deal of stress on the head of the baby
Neonatal Characteristics
• Two neonatal characteristics highly related to a
child’s risk of developing retardation: birth weight
and gestational age
• Gestational age refers to the age of a fetus
calculated from the time of conception
• Low birth weight and inadequate gestational age
at birth (prematurity) are perhaps the most
common neonatal risk factors
Causation during Infancy and
• Genetic disorders that cause developmental
damage to the neurological system
• Psychosocial or environmental factors,
where adequate stimulation to promote
intellectual and social growth does not exist
Treatment of children with mental
• Three types of prenatal intervention
– Chromosomal analysis for Down Syndrome or
other genetic abnormalities may result decision
to abort fetus
– Treatment for Rh blood incompatibility
between mother and fetus may prevent fetal
– Prenatal identification of a PKU problem may
result in maternal dietary restrictions
• Postnatal Interventions
– Infant stimulation programs provide positive
developmental environment for very young children
who are at risk because of prenatal or later
environmental circumstances
– Specific instruction for young children in language
skills appears promising and probably should be
implemented as early as possible
– Inclusion of young children of school age in classrooms
with non disabled peers
Prevention of Mental Retardation
• Because of the varied causes, prevention
efforts have been extremely diverse, and
some approaches have involved extremely
controversial methods
• In some cases, preventing mental
retardation requires courses of action that
are unacceptable to some segments of the
• A close relationship between medical personnel
and new parents is important in the prevention of
mental retardation
• PKU screening is now routinely undertaken when
a baby is born
• Prenatal screening and diagnosis can also lead to
preventive intervention that may be highly
controversial from a moral and ethical perspective