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While there are no tests that examine a newborn's DNA in the
first week of life, all babies in BC are offered a blood test
to check for genetic disorders. This is the ‘heel prick'
test and it currently checks for 4 diseases:
- Phenylketonuria (PKU)
- Galactosaemia (GS)
- Medium Chain Acyl-CoA Dehydrogenase
Deficiency (MCAD)
- Congenital Hypothyroidism (CH)
Early detection of these disorders allows treatment to begin
immediately. Treatments for these diseases are simple and
effective, and dramatically reduce or prevent permanent damage
as a result of these disorders.
PKU
This disorder occurs in 1/18,000 babies. It is an autosomal
recessive disorder where there is not enough of an enzyme
that breaks down phenylalanine. Phenylalanine is an amino
acid, one of the building blocks of protein.
When very little or no phenylalanine hydroxylase enzyme is
present, phenylalanine accumulates in the blood. It is toxic
to brain tissue. Without treatment, most infants with PKU
develop mental retardation.
The treatment is to avoid phenylalanine, especially while
the brain is developing but a life-long restriction is recommended.
Galactosaemia
Galactosaemia occurs in 1/30,000 babies. It is an autosomal
recessive disorder where the enzyme to break down galactose
is missing. The main dietary source of galactose is lactose,
found in milk. Babies are generally normal at birth but when
they start to have milk, most suffer from vomiting, jaundice,
diarrhea, and/or failure to thrive. Without the galactose-1-phosphate
uridyl transferase enzyme, galactose and galactose-1-phosphate
levels rise in the baby's blood and he/she becomes ill.
The treatment is to exclude galactose from the diet for the
rest of the child's life. The main source of this in the diet
is lactose in milk and milk products.
Medium chain acyl CoA dehydrogenase
deficiency (MCAD)
MCAD occurs in 1/20,000 babies and is also autosomal recessive
. Due to a lack of medium chain acyl CoA, people affected
with MCAD are unable to break down fats to make energy when
they run out of glucose.
As long as the children eat regularly, they are fine but they
can get very sick if not eating well. Fasting or infection
can trigger an episode of hypoglycemia that can be fatal.
There is a 30% risk of death after the first episode. Unfortunately,
sudden and unexplained death is often the first manifestation
of MCAD. It is estimated that up to 5% of deaths attributed
to Sudden Infant Death Syndrome may in fact be caused by undiagnosed
MCAD deficiency.
There is the possibility of fat accumulation in the liver
and brain even when the child is eating well because the enzyme
normally breaks down the medium chain fatty acids. Without
sufficient enzyme, break down does not occur and these fats
accumulate.
Again, the treatment is straightforward. Affected individuals
must avoid fasting so they don't rely on fats for energy.
This is particularly important during illnesses, even colds
and flu, where they may need more energy and/or have trouble
eating. It is also recommended that affected individuals reduce
their dietary fat to prevent accumulations.
Congenital Hypothyroidism
Approximately one in every 3000 to 4000 newborn babies have
congenital hypothyroidism. It is more common in girls than
boys, but the reason is still a mystery. It is not a genetic
disease, but it is one that is diagnosed at birth with the
‘heel prick' test.
Hypothyroidism means that not enough thyroxine (T4) is made
by the thyroid gland which is located in the front of the
neck just beneath the Adam's apple. Thyroxine is needed for
normal growth and development, especially in the first three
years of life when the brain and nervous system are rapidly
developing. If congenital hypothyroidism is not diagnosed
and treated soon after birth, it can cause mental handicap,
learning disabilities, and clumsiness.
The treatment for hypothyroidism is straightforward –
a synthetic version of thyroxine is taken to replace the missing
hormone in the affected child so they grow and develop normally.
March 2009
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