Causes of Intellectual Disability

EDU 248 Chapter 2 from Education of Students with an Intellectual Disability: Research and Practice; Foreman, Phil; 2009

Causes in Relation to Time

• Prenatal – before birth• Perinatal –at about the time of birth• Postnatal – following a child’s birth• Check out Table 2.1 on p. 24

Etiology (cont.)

• Etiology (causes) of intellectual disabilities was once thought to be biological and/or psychosocial• According to our author, etiology is now considered a mix of

“biomedical, social, behavioral, and educational risk factors”.• Social, behavioral, and educational risk factors are variables that may

lessen or prevent secondary disabilities. • The author describes several reasons that it is beneficial to know the

etiology of an intellectual or developmental disability on pp. 25-26

Parents as Partners

• The author suggests researching any intellectual disability of particular interest• He suggests that parents of children with intellectual disabilities are

likely to be well versed in their child’s disability• In planning a child’s educational journey, parents can provide a wealth

of information specific to their child’s disability

Prenatal Causes

• Prenatal causes of ID may be genetic• Prenatal causes of ID may have occurred during the gestational period• Rett syndrome and other similar problems cause some confusion –

degenerative problems happen postnatally, yet it is a genetic disease. • Other examples of prenatal causes of intellectual disabilities:• Chromosomal abnormalities

• Down syndrome – better educational prospects in recent years; goal of maximum personal independence in adult years with adequate literacy and numeracy skills

• Turner syndrome – found in girls; fewer incidences of intellectual disabilities associated with this syndrome, but likely to have some learning difficulties

Prenatal Causes (cont.)

• Inherited disorders• Dominant gene disorders need only be carried by one parent• Recessive gene disorders require both parents to be carriers• Geneticists can help parents determine chances of passing on an inherited

disorder• Dominant gene disorders that express themselves in serious physical or intellectual

disabilities generally die out; an exception – Apert syndrome• Children with Apert syndrome may have multiple physical disabilities but generally

have normal intellect.

• Key point! One must not assume that a child with serious physical disabilities also has intellectual disabilities.

Prenatal Causes (cont.)

• Inherited disorders (cont.)• Recessive gene disorders – • PKU requires 2 carrier parents to pass on the recessive gene. It rarely causes

intellectual disabilities in developed countries because a simple blood test for newborns identifies this disorder. A special diet can prevent intellectual disabilities from developing• Lesch-Nyhan disease (LND) – a recessive gene disorder that may cause

intellectual, physical, and behavioral disabilities (including self-mutilation and aggression) in boys, but is passed through girls.• Fragile X syndrome – discovered about 45 years ago, but is the most common

form of inherited intellectual disabilities; educational interventions may need to focus on behaviors and communication

Prenatal Causes (cont.)

• Multifactorial transmission – just as the names suggests, several genes are associated as a cause, perhaps in conjunction with environmental factors• “Cultural-familial” intellectual disability – generally associated with parents

who have a mild disability have children with mild intellectual disabilities; also likely to have poor education, live in poverty, and/or have difficulties parenting; early intervention strategies would include help related to the environmental factors• See “Kaylah’s Story” on p. 35.

Prenatal Causes (cont.)

• Developmental/Neural Brain Disorders • Spina Bifida – neural tube defect believed to have multifactorial causes;

research suggests there is genetic involvement that is affected by environmental factors, such as lack of folic acid in mother’s diet, obesity, diabetes, and some medications; 4 kinds of spina bifida, with myelomeningocele having the most significant physical disabilities.• Anencephaly – most of the brain is missing; will result in spontaneous

abortion (miscarriage), stillbirth, or neonatal death• Encephalocele – part of the brain protrudes from the skull

Prenatal Causes (cont.)

• Developmental/Neural Brain disorders (cont.)• Myelomeningocele spina bifida (cont. about – hydrocephalus may require a

shunt to remove excess fluid from the brain• Some children with spina bifida may have some mild intellectual disabilities• Children likely to attend regular school, use wheelchairs and accompanying

medical issues, have lower average intelligence or other learning and attention difficulties• Goals for mobility and general self-care, physical and occupational therapy,

and general education are appropriate

Prenatal Causes (cont.)• Maternal Infections• Rubella – once a leading cause of sensory and intellectual disorders in babies

born to mothers who contracted Rubella (German measles) during the first trimester of their pregnancy• Immunizations in most developed countries has decreased the numbers of

children born who have been affected by Rubella in utero• Toxoplasmosis – high risk of having a child who is deaf, has microcephaly, or

intellectual disabilities; thought to be contracted from cats and handling and eating undercooked meats• Cytomegalovirus – common virus with potentially harmful effects on the fetus

of pregnant women; causes sensory and/or intellectual disabilities• Cerebral palsy – studies indicate that 40% of mothers with children having CP

had a serious infection while pregnant; further studies need to be done in this area

Prenatal Causes (cont.)• Maternal toxicity –• Fetal Alcohol syndrome (FAS) and Fetal Alcohol Effects (FAE) are the most

preventable intellectual disabilities and the most common cause of intellectual disabilities; caused by maternal consumption of alcohol during pregnancy• There are common characteristics of children with FAS including

microcephaly, facial abnormalities, growth problems, and central nervous system disorders• There is evidence that genetics impacts the severity of problems associated

with maternal alcohol consumption• There is variability in the severity of disabilities associated with exposure to

maternal alcohol consumption (FAE is less severe)

Prenatal Causes (cont.)

• Maternal Toxicity (cont.)• FAS and FAE (cont.) • There are generally environmental factors associated with alcoholic mothers, but

problems with FAS and FAE will continue even if environmental factors are addressed

• Children may exhibit intellectual disabilities ranging from mild to severe, problems with executive function, speech and language difficulties, memory problems, attention deficit disorder, social and behavioral disorders, and mental health issues

• Classroom recommendations include behavior support, specific problem solving instruction, structure and routines, and a multidisciplinary approach; diplomacy is necessary because of the direct link to maternal alcohol abuse during pregnancy

Prenatal Causes (cont.)

• Other teratogens• Thalidomide – a prescription drug that caused numerous developmental

disorders in the 1950s and 1960s that increased awareness of maternal toxicity on developing fetuses

• Prescription drugs - women on prescription drugs should seek medical advice prior to becoming pregnant and during pregnancies

• Tobacco and recreational drugs – increased risk of low birth weight babies and premature births

• Other prenatal causes• Congenital hypothyroidism – related to maternal malnutrition, but rare in

developed countries and with iodized salt• Maternal prenatal trauma -