Mental Retardation

Contents : Definition Prevalence Classification Causes Clinical Evaluation Investigation Management

Definition Mental Retardation is defined statistically as tested cognitive performance that is two standard deviation below the mean of the general population ( roughly below the 3rd percentile )

The Classical definition comprises 3 components : 1- subaverage intellectual function . 2- that result from an injury , disease or abnormality before the age of 18 years . 3- resulting in impaired ability to adapt to the environment .

Prevalence : Mental retardation is present in about 2 to 3% of the population.

AAMR Classification Scheme IQ classification: I.Q.(intelligence quotient) is 100; normal ranges from 90 to 110 1-Border line { IQ 70-80 } 2-mild MR { IQ 55-70 } 3-moderate MR{ IQ 40-55 } 4-sever MR { IQ 25-40 } 5-profound MR { IQ below 25 }

Etiology Unknown “ 30-40 % “ Genetic “ 5% “ Early embryonic ( prenatal ) “ 30% “ Prematurity , IUGR (perinatal) “ 10 % “ Acquired medical condition (trauma , infection ..) “ 5% “ Environment “ 5-20% “

Etiology classification : Prenatal Perinatal Postnatal

Prenatal causes : »Genetic Disorders : Fragile X syndrome FXS :most common cause . Klinefelter syndrome :male with extra x chromosome 47,XXY Down syndrome : Meabolic disorders: PKU, Tay-sachs, Galactosemia Skin disorders : neurofibromatosis and Tubererous sclerosis . Prader-Willi Syndrom : Endocrine : hypothyroidism

Fragile X syndrome (FXS) Is the commonest cause of MR. The incidence has been estimated at approximately 1 in 1,500 males and 1 in 2,500 females. Mutation of a gene on the long arm of the X chromosome is responsible for FXS and involves instability of trinucleotide repeat sequence . DNA-analysis of the FMR-I gene is the best way to diagnose which is usually done on lymphocytes.

Fragile X syndrome (FXS)cont.. C/P: { phenotype } Large ears , Large testes (testicular volume>30 ml in adults) , Plantar crease , Hyperextensible joints , Simian crease, Broad forehead, Increased hand width, Increased hand length , Elongated face, High arched palate , Mitral valve prolapse , Hypotonia , Hernia, Double jointed thumbs , Scoliosis and Flat feet

Fragile X syndrome (FXS)cont.. C/P: {NEUROCOGNITIVE } Mental retardation , Hyperactivity , Attentional problems , Language delays , Hand flapping , Hand biting , Irritability , Perseveration , Excessive temper tantrums Gaze avoidance , Sensory aversion , Self-stimulatory behavior and Autism

»Cranial Malformations : Anencephaly : microcephaly : Hydrocephaly :

»Congenital Factors : Maternal : Rubella , congent. Syphilis & Rh incompitability Toxins : drugs , fetal alcohol syndrom ..

Perinatal Causes :  Low Bwt : premature , teen pregnancy , poor nutrition .. 21 % with MR Birth Anoxia : breech presentation , knotted umbilical cord.

Postnatal Causes : Child abuse and neglect : Traumatic brain injury : Infection : meningitis and encephalitis Nutritional deficiencies : Cultural and familial :

Clinical Evaluation Complete History : Examination :

»complete and detailed history« complete systemic review surgical history : trauma , accidents medical illnesses : hospitalization , general heath pregnancy history : maternal age , parity , infections.. birth : type , wt . GA ,complications , apgar score Postnatal : incubator , ventilator , disease ..

History (cont.) drugs: mother and child developmental Hx : mile stones , loss it , speech .. educational Hx : schooling , IQ tests behavioral Hx : skills , attention , activity family Hx : consanguinity , inherited ds .. social Hx :

»complete and detailed examination« Growth parameters : Dysmorphic features : CNS examination : Other system and skin exam : IQ tests : Developmental testing :

Investigations »» there is no specific investigation for MR but good hx and physical examination guide us toward the proper one «« DNA analysis: chromosomes FISH probes: Prader-willi,wiliams,cri du chat syndrom Metabolic labs:plasma a.a. , urine organic a. ,TFT , ck Imaging : brain MRI , CT , skeleton films Psychological Assesment: Electrophysiology : EEG , auditory & visual evoked potentials

When to do the investigations? Cytogenetic studies if: Microcephaly Multiple (even minor) somatic anomalies Family history of mental retardation Family history of fetal loss IQ <50 Skin pigment anomalies (mosaicism) Suspected contiguous gene syndromes (e.g., Prader-Willi, Angelman, Smith-Magenis)

Metabolic studies if : Episodic vomiting or lethargy Poor growth Seizures Unusual body odors Somatic evidence of storage disease Loss or plateau of developmental skills Movement disorder (choreoathetosis, dystonia, ataxia) Sensory loss (especially retinal abnormality) Acquired cutaneous disorders MRI of the brain if : Cerebral palsy or motor asymmetry Abnormal head size or shape Craniofacial malformation Loss or plateau of developmental skills Multiple somatic anomalies Neurocutaneous findings Seizures IQ <50

»» there is no specific Rx for MR «« Management of MR »» there is no specific Rx for MR «« »General rules : -Identify the cause then initiate a comprehensive plan -Special educator , Language , behavioral and occupational therapists -Special school programs -Community services