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Intellectual disability can sometimes be passed down from parent to child, depending on the cause. If intellectual disability runs in the family, they may be curious about what could happen with their potential future children.
Contracting[]
- What is your understanding of why you were referred?
- What is your main concern?
- I understand that some members of your family have intellectual disability
- Do you know what caused their intellectual disability?
- You were referred to GC because sometimes there is an underlying genetic condition that is the cause intellectual disability
- Sometimes a cause of intellectual disability remains unknown
- Obtain prenatal history
Family background[]
- Learning problems or intellectual disability?
- Were they in special classes at school?
- Do they live with someone who cares for them?
- Do you know of any tests that were done to try and determine the cause?
- Developmental delays
- Birth defects (heart defects, cleft lip or palate)
- History of pregnancy losses
- Anyone who died young or unexpectedly
- Chronic health problems
- Anyone with seizures
- Anyone with speech problems
Etiology of intellectual disability[]
There are many potential causes of intellectual disability. Common causes include genetic syndromes, multifactorial conditions, environmental exposures, infections during pregnancy, drug and alcohol use during pregnancy, problems with the birth or delivery, and prematurity. Still, in some cases, the cause is unknown.
- In mild intellectual disability, a specific risk factor has been identified in about 43% of the cases studied. Only 24% of these cases yield a fairly clear or convincing diagnosis. 2, 3 Of those, 14% are classified as genetic and 10% environmental.
- With moderate-severe intellectual disability, a cause is determined in up to 64% of cases with 45% of those being linked to genetic causes and 19% to environmental factors. 4
- The seemingly lesser role of genetics in milder intellectual disability may have something to do with the fact that some who fall into the mild intellectual disability category may simply represent the low end of the normal range of human intelligence.
- Severe intellectual disability is more likely to have a genetic component (50% of cases have a major chromosomal cause).
Genetic conditions[]
- Down syndrome accounts for 5% of mild intellectual disability cases and 30% of severe intellectual disability cases, 6, 7
- telomere deletions or duplications account for about 7.5% of intellectual disability 19
- Fragile X is seen in 5% of both mild and moderate-severe intellectual disability. 8, 9
- more than 500 other genetic diseases, mostly very rare, have also been associated with intellectual disability 10
Incidence[]
- 2-3% of the general population is affected with some level of intellectual disability
- 85-90% of patients with intellectual disability fall into the mild range (IQ of 50-70)
- Most live at home or in the community and have some level of independence.
Odds of a future child with intellectual disability[]
This is largely dependent on the cause of the intellectual disability.
- If cause is unknown, recurrence can be quoted as 1-25%, (this takes into account causes ranging from a non-genetic environmental exposure to an autosomal recessive condition)
- Studies have shown that a couple who has had one child with intellectual disability are about ten times more likely to have another
- Study at Greenwood genetic center preliminary results
- 452 probands with average IQ of 41.1 and head circumference in 43%ile with idiopathic intellectual disability and a subsequent sibling
- 502 male and 468 female subsequent sibs
- 21% of brothers and 14% of sisters also had intellectual disability.
- Recurrence in blacks was 18.3% and whites 17%
- Higher recurrence risks were positively correlated with higher IQ
- Question remains of whether it is genes, environment or a combination
Clinical Features[]
- Mild intellectual disability: IQ 50-70
- Moderate intellectual disability: IQ 35-50
- Severe intellectual disability: 20-35
- Profound intellectual disability: IQ less than 20
Testing[]
- IQ testing and a developmental assessment are common first steps
Psychosocial Issues[]
- Provision of adequate services
- Readiness to care for the child for the rest of their life
- Impact on siblings and other family members (positive and negative)
- Difficult feelings (denial, disappointment, loss, grief)
- Interruption of career goals, family routines, or plans for the future
- Financial and insurance issues
References[]
- Taking the Challenge: Finding Recurrence Risks in Idiopathic intellectual disability. J.S. Collins, A.F. Nave, G.A. Satten, R.E. Stevenson. Greenwood Genetic Center, Greenwood, SC;
- Centers for Disease Control and Prevention, Atlanta, GA. http://www.faseb.org/genetics/ashg01/f243.htm
- Genetics and [intellectual disability]. V. Reid Sutton, M.D. (article found at www.thedoctorwillseeyounow.com/articles/other/mr_16/)
Notes[]
The information in this outline was last updated in 2002.
This material has been imported from the wikibook "Genetic counseling"[ http://en.wikibooks.org/wiki/Genetic_counseling] under the GNU Free Documentation License.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License." |