Intellectual Disability

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:
1- Dysfunction of the CNS (structural, metabolic, genetic, infection,
hypoxic ischemic injury).
2- Experiential defect (family disorganization and poverty, parental
psychopathology).
Etiology:
Cause Examples % of total
Chromosomal disorders Trisomies 21,13,18, Klinefelter 22
Genetic syndromes Fragile X, Prader-Willi 21
Unknown Cerebral Palsy 21
Developmental brain abnormalities Hydrocephalus ± Meningomyelocele 9
Inborn error of metabolism PKU, Tay-Sachs 8
Familial Environment, syndromes, Genetic 6
Postnatal causes Trauma, Meningitis, Hypothyroidism 5
Congenital infections Toxoplasmosis, Rubella, CMV, HIV 4
Perinatal causes HIE, IVH,PVL, Meningitis 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, intra- cranial 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 (Tri- nucleotides 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.