Mental Retardation
DefinitionMental Retardation is cognitive performance that is two standard deviation below the mean of the general population (below the 3rd percentile ) Deficits in IQ and adaptive functioning IQ of 70 or below
Degrees of Impairment (DSM-IV) diagnostic &statical manual of mental disorder
Mild MR (IQ of 55 to 70) applies to about 85% of persons with MR typically not identified until elementary school years Moderate MR (IQ of 40 to 54) applies to about 10% of persons with MR usually identified during preschool years applies to many people with Down syndromeDegrees of Impairment (cont.)
Severe MR (IQ of 20 to 39) applies to about 3%-4% of persons with MR often associated with organic causes usually identified at a very young age Profound MR (IQ below 20 or 25) applies to about 1%-2% of persons with MR usually identified in infancy almost always associated with organic causes and often co-occurs with severe medical conditionsCauses of Mental Retardation
Causes of Mental RetardationDown’s Syndrome Most common chromosomal abnormality leading to MR (1.2/1000 births)Nondysjunction of chromosome 21Relative strengths:Visual (vs. auditory processing)Social functioningRelative weaknesses:Language expression and pronunciationGenerally viewed to suffer less severe psychopathology than other developmentally delayed groupsAfter 40 years of age, affected individuals nearly always demonstrate postmortem neuronal defects indistinguishable from Alzheimer’s Disease
Down’s Syndrome
Fragile X SyndromeFMR-1 gene (>200 trinucleotide CGG repeats, Xq27.3)An example of a “dynamic mutation” where more mutations occur with successive generationsGeneral problems: MR, mild CT dysplasia, & macro-orchidismOnly 50% of females with the full mutation demonstrate IQs in the borderline/mild MR range (vs. 100% of males)Increases the risk for ADHD, autism (20-60%) & social phobiaIncreasing deficits in adaptive and cognitive functioning with age
CF
Long face & large floppy ears. Macrocephaly & Macro-orchidism. Epilepsy & MR ( moderate ,severe) CT dysplasia ( extensible finger JJ, MVP) Autism DX: Cytogenetic analysis.(for repeats)
Fragile X Syndrome
Fragile X SyndromePhenylketonuria
Genotype:AR disease due to Mutation of the enzyme, phenylalanine hydroxylase (PAH) that hydroxylate phenylalanine to Tyrosine.Phenotype:Mental Retardation, Seizures, Fair Skin, “Mousy Odor” & Eczema.PHENYLALANINE HYDROXYLASE
PHENYLALANINEDietry sources, particularly plant proteins
BODY PROTEINS
BREAKDOWN
(b)
(a)
The normal metabolism of phenylalanine (pathways a and b)
TYROSINE
HYDROXYPHENYLACETIC ACID
PHENYLACETIC ACID (Brain)*
(c)
(c)
The abnormal metabolism in phenylketonuric subjects (pathway c)
*Agents, thought to be responsible for mental retardation
PHENYLALANINE*
Dietry sources, particularly plant proteins
BODY PROTEINS
(b)
(a)
PHENYLALANINE HYDROXYLASE
HYDROXYPHENYLACETIC ACID*
Normal at birth At 2 month (Vomiting, lethargy) Light hair, eyes, and skin Eczema-like rash Seizures (Hypsarrythmia) Hyperactivity Hypertonia and hyper-reflexia. Unpleasant musty/ mousy body odor Mental retardation & microcephaly.Symptoms of PKU