Mental retardation

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 :

History

»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 :

Examination

Investigations

When to do the investigations?

Cytogenetic studies if:MicrocephalyMultiple (even minor) somatic anomaliesFamily history of mental retardationFamily history of fetal lossIQ <50Skin pigment anomalies (mosaicism)Suspected contiguous gene syndromes (e.g., Prader-Willi, Angelman, Smith-Magenis)


Metabolic studies if :Episodic vomiting or lethargyPoor growthSeizuresUnusual body odorsSomatic evidence of storage diseaseLoss or plateau of developmental skillsMovement disorder (choreoathetosis, dystonia, ataxia)Sensory loss (especially retinal abnormality)Acquired cutaneous disorders MRI of the brain if :Cerebral palsy or motor asymmetryAbnormal head size or shapeCraniofacial malformationLoss or plateau of developmental skillsMultiple somatic anomaliesNeurocutaneous findingsSeizuresIQ <50

Management of MR