Intellectual Disability
Definition: Group of disorders that have in common deficits of
adaptive and intellectual function and an age of onset before maturity is
reached.
Dementia: Degeneration of fully developed mind.
Diagnostic Criteria:
• IQ score of two standard deviations (SD) below the mean, 70 or
below.
• Impairments in the present adaptive skills: a significant delay in 2
of the 10 areas must be present (communication, self-care, home
living, social and interpersonal skills, use of community resources,
self-direction, functional academics, work, leisure, and health and
safety)
• Onset before age 18 years.
Epidemiology: 2.5% of the general population have IQ less than 2 SD
below the mean. 85% of the patients with intellectual disability are in the
mild rang, 0.3-0.5% are in the severe range of intellectual disability. The
mild intellectual disability prevalence varies inversely with the
socioeconomic state, while the moderate-severe intellectual disability are
equal in all the socioeconomic states. The incidence of intellectual
disability increased initially with the age and increased sharply in the
early school years and then declining in the adolescence. intellectual
disability occurs more frequently in males than girls:2:1 in mild
intellectual disability and 1.5:1 in severe intellectual disability.
Pathogenesis:
12-
Dysfunction of the CNS (structural, metabolic, genetic, infection,
hypoxic ischemic injury).
Experiential defect (family disorganization and poverty, parental
psychopathology).
Etiology:
Cause
Chromosomal disorders
Genetic syndromes
Unknown
Developmental brain
abnormalities
Inborn error of metabolism
Familial
Postnatal causes
Congenital infections
Perinatal causes
Examples
Trisomies 21,13,18, Klinefelter
Fragile X, Prader-Willi
Cerebral Palsy
Hydrocephalus ± Meningomyelocele
% of total
22
21
21
9
PKU, Tay-Sachs
Environment, syndromes, Genetic
Trauma, Meningitis, Hypothyroidism
Toxoplasmosis, Rubella, CMV, HIV
HIE, IVH,PVL, Meningitis
8
6
5
4
4
Classification
(1): According to the cause and pathology.
(2): According to the I.Q:
a- MR with unspecified severity( IQ is untestable by standard tests).
b- Profound (<20-25).
c- Severe (20-25 to 35-40).
d- Moderate (35-40 to 50-55)
e- Mild (50-55 to 70)
(3): According to the sub normality (Subnormal, Severe subnormal).
(4): According to the educational terminology (Unsuitable for education).
(5): According to the support needed in daily activities (Pervasive,
Extensive, Limited, Intellectual) support.
(6): According to the scientific terminology (Idiot, Imbecile, and Feeble
minded).
Clinical manifestations:
Age
Common presentations
Newborn
Dysmorphic syndromes, Microcephaly, Abnormal
feeding or breathing
Early infancy (2-4mo) Failure to interact with environment, concern about
vision and hearing
Late infancy (6-18mo) Gross motor delay
Toddlers (2-3yr)
Language delay or difficulties
Preschool (3-5yr)
Language delay or difficulties, Behavior difficulties
including play, Delay in fine motor Skills like drawing
School age (>5yr)
Academic underachievement, Behavior difficulties
( attention anxiety, mood…)
Prevention
(1): Increasing the public awareness about the risk of alcohol and other
drugs on the fetus.
(2): Preventing teen pregnancy and promoting early prenatal care.
(3): Preventing traumatic injuries.
(4): Preventing poisoning.
(5): Preventing sexual transmitted diseases.
(6): Immunization programs.
(7): Newborn screening for metabolic diseases and hearing screening.
Stigmata associated with MR:1-Characteristic faces: (Down, Hypothyroidism, Hurler, Microcephaly,
Hydrocephaly, Hypercalcemia and Sturge-Weber
syndrome).
2-Skin lesions: (NFM, Tuberous sclerosis and Sturge-Weber syndrome).
3-Eye defect:
A-Bilateral cataract (Down, Congenital rubella, Galactosemia and
Hypoparathyroidism)
B-Retinopathy (Congenital rubella, Toxoplasmosis).
C-Lens dislocation (Upward dislocation in Marfans syndrome,
Downward dislocation in Homocystineuria).
D-Corneal opacity (Hurler syndrome).
E-Brush field spots (Down syndrome).
F-Kayser-Fleischer ring (Wilson disease).
4-CHD: (Down, Edward, Pateau, Turner, Congenital rubella and
idiopathic hpercalcemia).
5- Hepatosplenomegaly: (Glycogen storage diseases, Galactosemia,
Mucopolysaccaridosis, Congenital rubella,
CMV and Toxoplasmosis).
Diagnosis
It require an IQ of (70-75) or below, in association with a defect in
adaptive skills like (self-care, communication, home living, functional
academies…etc.).
(1): History (prenatal, perinatal, postnatal) and family history.
(2): Presentation (physical stigmata, developmental delay, abnormal
behavior and convulsion).
(3): Vision/ Hearing evaluation.
(4):Neuro imagining:
a- Skull X-ray for (shape of sella tursica, sign of increased I.C.P, intracranial calcification which is seen in:●Normally in pineal body and choroid plexus .
●
Abnormally
in
(subdural
hematoma ,craniopharyngioma,
hypoparathyrodism, CMV, aneurysm, hydatid cyst, tuberous sclerosis and
sturge-weber syndrome).
b- MRI, which will yield 40-55% of causes. (3): Vision/ Hearing
evaluation.
(5): Karyotyping, which will yield 3.7% of causes.
(6): Fragile X screen, which will yield 2.6% of causes.
(7): T4,TSH, which will yield 4% of causes.
(8): Serum Lead
(9): Metabolic tests ,which will yield 1% of causes.
(10): Subtelomeric deletions, which will yield 6.6% of causes. It obtain in
the presence of dysmorphism but with a normal karyotype and
fragile X DNA study
(11): EEG which will yield 1% of causes.
Management: It is multidimensional and highly individualized.
(1): Family (don’t tell them the diagnosis until you are sure and prove it.
(2): Genetic counseling.
(3): Good nursing.
(4): Early detection and prevention.
(5): Drugs like anticonvulsant.
(6): Employment.
(7): Especial education and therapeutic device.
(8): Prepare for future problems.
(9): Routine health maintenance.
Fragile X- syndrome
It accounts for 3% of the cases of males with MR. The fragile site located
on distal long arm of chromosome X. The inheritance is due to (Trinucleotides repeat expansion CGG, which is called allelic expansion).
With additional of (600-3000) base pairs, BP, more than normal, which is
constitute of (2800) repeated Tri nucleotides base.
If the addition is (50-600) BP, it will result in carrier state.
This expansion increased gradually in size when transmitted by females,
but remains the same when transmitted by males.
C.F: MR, autistic behavior, Macroorchidism, which may not be evident
until puberty, long face, prominent jaw and large prominent ears. The
female shows only varying degrees of MR.
Diagnosis: DNA studies, which demonstrate, expanded segment of DNA.