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Why does mental
retardation occur? As noted earlier, anything that damages and interferes
with the growth and maturation of the brain can lead to mental retardation.
There can be hundreds of such causes. This might happen before, during or
after the birth of the child. While a few examples are explained below, a
more detailed list of causes is given in Table 2.
Machi
Pelha
Table 2:
Causes of mental retardation
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Category
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Type
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Examples
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Prenatal
(causes before birth)
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Chromosomal disorders
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Downs syndrome*, Fragile X syndrome,
Prader Wili syndrome, Klinefelters syndrome
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|
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Single gene disorders
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Inborn
errors of metabolism, such as galactosemia*, phenylketonuria*, mucopolysaccaridoses
Hypothyroidism*, Tay- Sachs disease
Neuro-cutaneous
syndromes such as tuberous sclerosis, and neurofibromatosis
Brain malformations such as genetic microcephaly,
hydrocephalus and myelo-meningocele*
Other dysmorphic syndromes, such as Laurence
Moon Biedl syndrome
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Other conditions of genetic origin
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Rubistein Tabi syndrome De Lange syndrome
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Adverse material / environmental influences
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Deficiencies*
, such as iodine deficiency and folic acid deficiency
Severe malnutrition* in pregnancy
Using substances * such as alcohol (maternal alcohol syndrome), nicotine,
and cocaine during early pregnancy
Exposure* to other harmful chemicals such as
pollutants, heavy metals, abortifacients, and
harmful medications such as thalidomide, phenytoin
and warfarin sodium in early pregnancy
Maternal infections such as rubella*, syphillis*,
toxoplasmosis, cytomegalovirus
and HIV Others such as excessive
exposure to radiation*, and Rh
incompatibility*
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Perinatal (around the time of
birth)
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Third trimester ( late pregnancy)
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Complications
of pregnancy*
Diseases* in mother such as heart and kidney
disease and diabetes
Placental dysfunction
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Labour
(during delivery)
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Severe
prematurity, very low birth weight, birth
asphyxia
Difficult and/or complicated delivery*
Birth trauma*
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Neonatal (first four weeks of life)
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Septicemia,
severe jaundice*, hypoglycemia
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Postnatal (in infancy and childhood)
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Brain
infections such as tuberculosis, Japanese
encephalitis, and bacterial meningitis
Head injury*
Chronic lead exposure*
Severe and prolonged malnutrition*
Gross understimulation*
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Note: conditions marked
with an asterisk are definitely or potentially preventable.
Some common causes of mental retardation
Downs Syndrome: The human body is
made up of billions of cells. Each cell contains 46 thread-like structures
called chromosomes. In Downs
syndrome, because of a biological error around the time of conception, the
cells come to have one extra chromosome i.e, 47
instead of 46 chromosomes. The presence of an extra chromosome in the cells
interferes with the normal development of the brain, leading to mental
retardation. Downs syndrome is a common cause of
mental retardation. It is often possible to recognize people with Downs syndrome by their facial appearance,
characterized by up-slanting eyes and flat bridge of the nose. Downs
syndrome occurs in about 1 in 800 newborn babies. Even though it is a genetic
disorder, Downs syndrome is
most often not inherited and can occur in any child. However, it is more
likely to occur when the age of the mother at the time of the birth of the
child is over 35 years.
Even though persons with Downs
syndrome have mental retardation, they possess good social and interactional skills.
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Mothers older than 35 years of age may consider
antenatal genetic screening for diagnosis of Downs
syndrome in the unborn child.
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Inherited
Metabolic Disorders: Chromosomes in the
human cells contain genes which control growth and maturation of the brain.
Some of these are responsible for chemical (metabolic) reactions, which are
essential for brain growth. If such a gene is abnormal, it can lead to
derangement of metabolic reactions and thereby cause mental retardation. Phenylketonuria is one such condition. Babies with phenylketonuria, in addition to mental retardation, have
light-coloured hair and skin, a small head, and are
prone to convulsions.
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Detection of phenylketonuria at
birth and proper dietary treatment can prevent brain damage and help babies
to grow normally.
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Maternal Rubella Syndrome: Rubella or German measles is
generally a harmless viral infection in adults, producing symptoms of mild
fever, rash, and enlargement of lymph nodes. But when it occurs for the first
time during early pregnancy, the virus spreads to the baby growing in the
mother's womb and causes extensive damage. When such a baby is born, it is
likely to have mental retardation and visual impairment.
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Maternal rubella syndrome is preventable by immunizing
children with rubella vaccination (as part of MMR vaccination).
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Iodine deficiency
disorders are preventable by universal iodization
of salt.
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Iodine Deficiency Disorder (cretinism): Iodine is essential
for the normal development of unborn babies. Lack of adequate availability of
iodine from the mother restricts the growth of the brain of the foetus, and leads to a condition called hypothyroidism.
Babies with this problem have mental retardation, hearing impairment and
dwarfism. In addition, they may have lethargy, coarseness of facial features,
rough and dry skin, feeding problems, constipation, cold extremities, and
neck swelling because of enlargement of the thyroid gland. A severe form of
this condition, in which all the features mentioned are very pronounced, is
called cretinism.
Iodine occurs naturally in food. But in some places, the soil and the food
are deficient in iodine. In such places, naturally, a pregnant woman's intake
of iodine is less and therefore their infants would also be deficient in
iodine and manifest hypothyroidism. Iodine deficiency is prevalent in large
areas in some Member Countries of SEAR.
Difficult/Complicated Delivery: Till they
are born, babies receive their supply of food and oxygen from the mother.
Immediately after birth, babies begin to breathe on their own. Normally, this
transition occurs smoothly. When, for any reason, the delivery becomes
difficult, prolonged, or complicated, oxygen supply to the baby is
diminished. As the brain is very sensitive to oxygen deprivation, this can
result in brain damage. This is called birth asphyxia. Such babies may have
problems in development such as mental retardation or cerebral palsy.
Brain Infection (Brain Fever): An important
cause of mental retardation after birth is brain infections caused by
bacteria or viruses. In this condition, children who are otherwise normal,
suddenly develop fever, headache, vomiting, convulsions and loss of
consciousness. If this infection is severe, there may be irreversible brain
damage leading to mental retardation. Such children, when they recover from
acute illness, are noticed to have lost many skills which they had learnt
earlier. Young children are more at risk for brain fever in regions where
Japanese encephalitis and tuberculosis are common.
Nutrition and Mental Development: A balanced diet rich in calories, protein,
vitamins and minerals is required for pregnant women and young children for
normal brain development. Lack of adequate diet can have direct and indirect
effects on brain development and thereby increase the risk of subnormal
development.
Studies have shown that birth weight is an important indicator of the future
health of the baby. A baby with low birth weight is more likely to have
problems in mental development. The height and weight of would-be mothers and
the extent of weight gain in pregnancy are important factors determining
birth weight.
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Proper nutrition of
the girl child and good nutrition for pregnant woman can prevent many
developmental problems in their babies.
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Yogeeta
Common health problems associated with mental retardation
Many children and adults with mental retardation are
otherwise physically and mentally healthy, except that they have lower
intelligence. Several others, however, frequently have other problems. The
common health problems associated with mental retardation are as follows:
Behaviour problems: Symptoms
like restlessness (continuously moving around; unable to sit in one place),
poor concentration, impulsiveness, temper tantrums, irritability and crying
are common. Other disturbing behaviour, like
aggression, self-injurious behaviour (such as head
banging) and repetitive rocking may also be seen. When such behaviour is severe and persistent, it can become a major
source of stress for families. Therefore, attention should be paid to reduce
such behaviour while providing treatment and care.
Convulsions: About 25% of people with mental retardation
get convulsions. Many types of convulsions can occur involving the whole
body, or only one half of the body, or sudden single jerks leading to a fall.
Convulsions, although alarming to watch, can be easily controlled with proper
medication.
Sensory impairments: Difficulties in seeing and hearing
are present in about 5-10% of persons with mental retardation. Sometimes
these problems can be resolved by using hearing aids or glasses, or
undergoing surgery for cataract.
As noted earlier, other developmental disabilities, such
as cerebral palsy, speech problems and autism, can
occur along with mental retardation. Persons with many disabilities, or
multiple disabilities, pose a big challenge in terms of providing care.
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