Pediatrics clinical chemistry

Pediatrics involves both intrauterine
& extra uterine periods

Definitions
Child:
• Legal definition: A human being below the age
of 18 years unless under the law applicable to
the child, majority is attained earlier.
• Biological definition: Anyone in the
developmental stage of childhood, between
infancy and adulthood.

- Neonate: newborn up to first 28 days of life
- Infant: comprises neonatal period up to 12
months
- Toddler: 1-3 years
- Pre-school: 3-5 years
- School-age: 6-10 years
- Adolescent: 11-14 years

Some pediatrics clinical
chemistry reference intervals

- Laboratory evaluation starts from the
prenatal period.

- The most important clinical conditions are:
1) Evaluation of maturity.
2) Diagnosis of congenital abnormalities

Intrauterine Growth Retardation
(IUGR)
AGA (Appropriate for Gestational Age):
Birth weight is between 10th and 90th percentile for
infant’s gestational age (GA).
SGA (Small for Gestational Age):
Birth weight <10th percentile for GA.
IUGR (Intra Uterine Growth Retardation):
Deviation and reduction in expected fetal growth
pattern.

Not all IUGR infants are SGA

ASYMMETRIC vs. SYMMETRIC
GROWTH RETARDATION
- Most growth retarded infants have
asymmetric growth restriction. First there is
restriction of weight and then length, with a
relative “head sparing” effect.
- This asymmetric growth is more commonly due
to extrinsic influences that affect the fetus
later in gestation, such as preeclampsia,
chronic hypertension, and uterine anomalies.

- In the human brain, most neurons develop
prior to the 18th week of gestation. Early
gestational growth retardation would be
expected to affect the fetus in a symmetric
manner.
- Examples of etiologies for symmetric growth
retardation include genetic or chromosomal
causes,
early
gestational
intrauterine
infections (TORCH) and maternal alcohol use.

CAUSES:
A. Maternal
• Low pre-pregnancy weight
• Recent pregnancy and/or high parity
• Chronic illness - such as malabsorption,
diabetes, renal disease
• Inadequate or poorly balanced dietary intake
• Decreased O2 availability to fetus (e.g., high
altitude, severe maternal anemia)

B. Uterine and placental factors:
Inadequate placental growth, uterine
malformations, decreased utero-placental blood
flow (e.g., toxemias of pregnancy, diabetic
vasculopathy) and multiple gestations
C. Fetal causes:
Include Chromosomal abnormalities and
intrauterine infections (i.e., TORCH)

The most important organ we are after for
maturity is the lung

Assessment of Fetal Lung Maturity:
-Fetal lung maturation is marked by production
of a detergent-like material, surfactant, which
forms a film on the alveolar surfaces.

-Prior to 35th week of gestation, the major
component of surfactant is α-palmitic β-myristic
lecithin.
- After
that
time,
dipalmitic
lecithin
predominates and phosphatidyl glycerol (PG)
appears about a week later.
- Minor phospholipid components of surfactant
include phosphatidyl inositol, phosphatidyl
ethanolamine, phosphatidyl serine, and
sphingomyelins.

-Since sphingomyelin (S) concentration in AF is
constant during the third trimester, it serves as a
reference material against which surfactant
lecithin (L) can be compared.
- Measurement of L/S ratio avoids problems
associated with variability in chemical extraction
and inaccuracy in estimates of absolute
concentration per AF volume

1) Quantification of Pulmonary Surfactant: L/S
Ratio (Lecithin / sphingomyelin):
-It is the most valuable assay for the assessment
of fetal pulmonary maturity.
-At 32 weeks the L/S ratio reaches 1. Lecithin
then rises rapidly, and an L/S ratio of 2.0 is
observed at 35 weeks.

- A ratio of 2.0 or greater has repeatedly been
associated with pulmonary maturity.

-A mature L/S ratio predicted the absence of RDS in
98 percent of neonates. With a ratio of 1.5 to 1.9,
approximately 50 percent of infants will develop RDS.
Below 1.5, the risk of subsequent RDS increases to 73
percent.
Other tests to evaluate surfactant:
- Evaluation of Amniotic Fluid Turbidity visually
- Shake Test
- Foam Stability Index
- Tap Test

2) Test for PG: Amniostat-FLM:
-A rapid immunologic semiquantitative
agglutination test that can be used to determine
the presence of Phosphatidylglycerol (PG)
- Results are reported as:
Negative
Low- positive (PG 0.5-2ug/ml)
High -positive (PG ≥2ug/ml)
- RDS rarely develops if PG is ≥2ug/ml

3) Fluorescent Polarization FLM Tests:
- The TDx analyzer is an automated fluorescence
polarimeter that determines surfactant albumin
ratio.
- The test requires 1 ml of uncentrifuged amniotic
fluid and can be run in less than 1 hour.
- The surfactant albumin ratio (SAR) is determined
with amniotic fluid albumin used as an internal
reference.
-A ratio of 50 to 70 mg surfactant per gram of
albumin is considered mature.
- Correlates with L/S and has a better precision.

4) Lamellar Body Counts:
- Lamellar bodies are the storage form of
surfactant.
- They scatter light & can be counted directly
using the platelet channel of most cell counters
- A lamellar body count >30,000/μl
uncentrifuged AF is highly predictive of
pulmonary maturity, while a count <10,000/μl
suggests a risk for RDS.
- Neither meconium nor lysed blood has an
effect on the lamellar body count.

Assessment of Premature Rupture of
Membranes

- Pre mature rupture of the membranes is the most
common cause for pre maturity.
- Diagnosing premature rupture of membranes is
done by:
1) PH assessment of vaginal discharge:
Unlike vaginal secretions whose pH is acidic, AF is
alkaline. The vaginal pool aspirate of a gravida with
watery discharge can be tested with nitrazine
paper to estimate pH visually.

2) An aliquot of the aspirated fluid can also be
applied to a glass microscope slide, dried for 5
minutes and examined microscopically for a
‘fern' pattern, which indicates the presence of
AF in the vaginal fluid pool.

3) Fetal fibronectin in maternal plasma or AF:
- Fetal fibronectin is a chorionic trophoblast
protein.
- If fetal fibronectin is increased in maternal
plasma or AF or cervicovaginal secretions
between 22-34 weeks gestation, it denotes loss
of integrity of the fetal membranes.
- A POC device is available at the obstetrician
office for measuring fetal fibronectin.
- It has a high predictive value for impending
early delivery of the baby & RDS

Sampling in pediatrics
Pre analytical considerations:
- Difficult sampling (Capillary; heal, thumb):
needs an expert
- Small patient’s size, number of times for blood
to be drawn for repeat analysis.
- Different sizes of tubes.

Recommended blood draw volumes for
pediatric patients

Choice of the analyzer:
- Dead volume? The smaller, the better
- Clot detector
- Sample cubs & primary tubes

Point of care analysis:
•
•
•
•
•
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Portable testing devices that are easy to use
Small sample volume
No sample preparation is required
Provide rapid bed side results
Can be connected to the hospital LIS
Mainly used for: bilirubin, glucose, Hb, electrolytes
& blood gases

Point of care analysis:
• High cost, so its use should be rationalized for tests
that needs short TAT
• Neither their performance nor their dynamic ranges
are as good as the tradition lab equipments.
• Should be properly validated using appropriate
quality assurance procedures
• Very low or very high results should be checked in
the main laboratory

The most important items that need
evaluation in pediatrics are:
1. Regulation of blood gases & pH.
2. Kidney function with regulation of water &
electrolytes
3. Liver function: physiologic jaundice & energy
metabolism
4. Calcium and bone metabolism
5. Endocrine functions
6. Genetic diseases & neonatal screening

1) REGULATION OF BLOOD GASES &PH
-Requires fully mature lungs & kidneys after
birth.
- Immature lungs or surfactant may result in
respiratory distress syndrome (RDS), where
there is failure in excreting CO2 resulting in
respiratory acidosis. (Plasma bicarbonate is not
affected early, before renal compensation takes
place)
-

- The trauma & relative anoxia during delivery
causes an increase in lactic acid production &
accordingly, metabolic acidosis. (Reduced
bicarbonate level, supplying bicarbonate
reverses the condition)
-Persistent acidosis that is not corrected by
bicarbonate administration is an indication for
possible inborn errors of metabolism.

-Alkalosis is uncommon in pediatric patients,
most common causes:
1) Hyperammonemia: Secondary to
diseases & inborn errors of metabolism
2) Pyloric stenosis & loss of gastric acids
3) Hypokalemia

liver

2) KIDNEY FUNCTION
- From the 35th week of gestation, rapid kidney
development takes place in preparation for extra
uterine life

GFR:
- At birth, GFR is about 25 % of its value in older
children.

- Tubular function shows a similar pattern,
where the concentrating power of the kidney
in the early months of life is only about 78 %
of its value in the adult kidney.

- This gradual process of renal development
results in serum electrolytes level shift seen in
the neonatal period.

- The kidney primarily maintains water
homeostasis
- Other causes of water loss in the neonatal
period:
1) Insensible water loss through the skin
2) The use of radiant heaters (radiated heat) to
maintain body temperature.
3) Insensible water loss from the lungs in RDS

Disorders affecting electrolytes and
water balance

3) Liver function
Physiologic Jaundice:
- The processing of many normal metabolic
pathways and the metabolism of exogenous
compounds proceed slower in neonates.
- The most striking effect of an immature liver, even
in a full term baby, is the failure to adequately
metabolize bilirubin.

- Fetal blood is produced first by the embryonic
yolk sac, then by the liver, and finally by the fetal
bone marrow.
- With the switch of erythropoiesis to the fetal liver,
fetal hemoglobin production begins.
- HbF consists of two α- and two γ-chains.
- As the fetal bone marrow begins red cell
production, HbA production increases.
- At birth fetal blood contains 75% HbF and 25%
HbA. HbF production rapidly diminishes during the
first year of postnatal life. In normal adults, less
than 1% of hemoglobin is HbF.

-HbF has a higher affinity for oxygen than does
HbA. Thus in the placenta, oxygen is released from
the maternal HbA, diffuses into the chorionic villi,
and binds to the fetal HbF.
-Bilirubin accumulates as fetal hemoglobin is
rapidly destroyed and replaced by adult
hemoglobin.
- At birth, UDP - glucuronoyltransferase, the
enzyme responsible for conjugating bilirubin, is
immature. This results in the accumulation of
unconjugated bilirubin and the development of
physiologic jaundice.

-A normal baby may have a serum bilirubin up to
15 mg / dl, most of it unconjugated. This level
should fall to the base line by the age of 10 days.
-If severe and passes the immature BBB, it might
lead to kernicterus (Bilirubin encephalopathy).
- Complete absence of the bilirubin conjugating
enzyme results in severe persistent jaundice
(Crigler – Najjar syndrome)

Carbohydrate metabolism:
-At birth, a full term baby has sufficient glycogen
stores to provide glucose as an energy source.
-If the delivery is stressful, these energy reserves
may become depleted prematurely.
- At that time, the normal physiologic rule of the
gluconeogenesis pathway becomes essential
where there is conversion of alanine into
glucose.

-The later pathway is not always mature at birth
which may result in what is termed “physiologic
hypoglycemia”.
- This condition usually corrects quickly as the
enzyme system matures.

-Persistent and severe hypoglycemia should
alert the physician towards a possible inborn
error of metabolism, such a galactosemia.
- Galactosemia is due to failure of conversion of
galactose to glucose as a result of genetic
deficiency in any of the following enzymes:
galactose-1-phosphate uridyltransferase (GALT),
galactokinase (GALK) or uridine diphosphate
galactose-4-epimerase (GALE)

Nitrogen metabolism:
-The liver is involved in the metabolic inter
conversions of amino acids and in the synthesis
of non-essential amino acids.
- The liver synthesis most of the plasma proteins
including albumin, transferrin, complements and
coagulation factors.

-Important in nitrogen metabolism through the
Urea cycle.
-Owing to the immaturity of urea cycle enzymes
early in life, the level of ammonia in the plasma
of neonates is highly elevated than its level in a
one year old child.

- Persistently elevated ammonia level, should
alert the investigator to possible liver damage.

4) CALCIUM AND BONE METABOLISM
- Normal bone growth requires integration of
calcium, phosphate and magnesium metabolism
with endocrine regulation from vitamin D,
parathyroid hormone & calcitonin.

-The active metabolite of vitamin D is 1,25
dihydroxy vitamin D.
-Hydroxylation of Vitamin D from diet takes
place in liver and kidneys and requires normal
functioning of these organs.

- Absorption of vitamin D from the
gastrointestinal tract, conversion to its active
form in the kidney, and incorporation of
calcium and phosphate into the growing bone
requires normally active PTH.

- Secretion of PTH is in turn modulated by serum
calcium & magnesium levels, where low level
of both divalent cations inhibits PTH secretion.

- Rapid bone growth occurring in infancy and
puberty requires optimal coordination of
mineral absorption, transport and endocrinecontrolled incorporation of the minerals into
growing bone.

- Approximately 98% of total body calcium is
present in bone and less than 2 % is
measurable in blood.

Hypocalcemia:
- Hypocalcemia is defined as total serum calcium
below 7.0 mg / dl or ionized calcium below 3.0
mg / dl.
- In the newborn, particularly immature, these
levels may be commonly encountered with
few symptoms. However, hypocalcemia can
result in irritability, twitching and seizers.
Serum calcium is usually measured in children
with seizers of unknown etiology.
- Prolonged hypocalcemia can result in reduced
bone growth and rickets.

Causes of hypocalcemia:
• Prematurity
• Metabolic acidosis
• Vitamin D deficiency
• Liver diseases
• Kidney diseases
• Hypoparathyroidism
• Low calcium intake
• High phosphorus intake
• Hypomagnesemia (Inhibits PTH secretion)

Rickets:
- Disease caused by a
mineralization defect during
bone formation resulting in
increase in osteoid, the
unmineralized organic matrix
Of bone.

Causes:
1. Vitamin D deficiency: inadequate exposure to
sun, poor vitamin D diet, malabsorption
2. End organ resistance to vitamin D
3. Phosphate depletion: e.g. Fanconi syndrome
Biochemical findings:
1. Low serum calcium & phosphates
2. High serum ALP (Due to increased osteoblastic
activity)
3. 25 (OH) D: to assess vitamin D status.

N.B:
- Vitamin D-dependent rickets type I is an
inherited defect in 25(OH) D-1α hydroxylase
causing impaired formation of 1, 25(OH)
vitamin D.
- Vitamin D-dependent rickets type II is an
inherited disorder characterized by very high
serum concentration of 1, 25(OH) vitamin D.
This syndrome is due to resistance to 1,
25(OH) vitamin D, secondary to defects in the
1,25(OH) vitamin D receptor.

Hypercalcemia:
- Defined as total serum calcium > 11.0 mg / dl.
- This is unusual in pediatrics, but has
potentially severe clinical implications.
- Patients with hypercalcemia have poor muscle
tone, constipation, failure to thrive and may
develop kidney stones leading to renal failure.

5) ENDOCRINE FUNCTION
Hypothalamic – pituitary – thyroid axis:
Primary hypothyroidism
(Congenital hypothyroidism):
- Results from any defect that causes failure of the
thyroid gland to synthesize and secrete thyroid
hormones.
- Incidence: 1/4000 births
- Untreated patients with this condition have severe
mental retardation with unusual facial features.

- Treatment by thyroid replacement therapy is
usually successful when diagnosis is
established.
- The best diagnostic test is to measure serum
TSH level which is high as a result of failure of
the long feedback loop (between pituitary &
thyroid gland). Thyroid hormone levels in
untreated patients are very low.
- The only neonatal screening program in Egypt.

Secondary hypothyroidism:
- It is a result of pituitary failure to secrete TSH
which results in lack of thyroid gland
stimulation and subsequent production of
thyroid hormones.
- Diagnosed by low TSH.
- It is important to study the other pituitary
pathways to determine whether this is an
isolated TSH defect or panhypopituitarism.

Neonatal Graves‘ disease:
-The fetal thyroid-pituitary axis functions
independently from the mother's axis in most
cases.
-However, if the mother has preexisting Graves'
disease, her auto antibodies can cross the
placenta and stimulate the fetal thyroid gland.
Thus the fetus can develop hyperthyroidism.
- Measurement of thyrotropin-binding inhibitory
immunoglobulins is useful for assessing risk of
fetal or neonatal Graves' disease.

Hypothalamic – pituitary – adrenal cortex axis:
- The most important disorder is congenital
adrenal hyperplasia (CAH)
- CAH: Congenital absence of one or more of the
synthetic enzymes that lead to cortisol and
aldosterone biosynthesis. This leads to
compensatory increase in ACTH leading to
stimulation of steroids biosynthesis till the block
point causing:

1. Hyperplasia of the adrenal cortex
2. Accumulation of intermediate compounds
proximal to the block
3. Shunting of the substrate towards the
adrenal androgen pathway
- The most common disorder is 21-Hydroxylase
deficiency (1 / 5000 births)

Growth factors:
- G.H deficiency results in poor growth and
stunted growth.
- When G.H acts on its receptors on the liver,
the liver secretes IGF-1 & its binding protein
IGF-BP3
- Due to the diurnal and pulsatile pattern of G.H
secretion, a single measurement is not
sufficient to diagnose its deficiency.

- Insulin induced hypoglycemia & clonidine
induced hypotension are common stimulatory
tests used to detect G.H deficiency.
- Measuring IGF-1 & IGF-BP3 is considered an
effective tool for assessing G.H deficiency
because:
1. Their basal levels do not have the great
variation that occurs for G.H
2. Infants with defects in IGF-1 & IGF-BP3
synthesis and secretion are unlikely to respond
to G.H replacement.

Screening for
diseases in
pediatrics

Screening for diseases in pediatrics:
I) Pre natal:
- Maternal screening
- Fetal screening:
amniocentesis, chorionic villi sampling & pre
implantation genetic diagnosis
II) Post natal

MATERNAL SERUM SCREENING FOR FETAL
DEFECTS:
Multiple of the median (MoM):
- The MoM is now universally used as a common
currency for converting analyte values into an
interpretative unit and is also the starting
point for calculating risks for neural tube
defects, Down syndrome, and trisomy 18.

- For each analyte, each lab should develop a
set of median values for each week (or day) of
gestation using the laboratory’s own assay
values measured on the population to be
screened.
- Individual test results are then expressed as
MoM by dividing each individual test result by
the median for the relevant gestational week.

Screening for Down syndrome (trisomy 21) &
trisomy 18:
First trimester screening (Double test) –
[11th- 14th gestational weeks]
- Combining two serum markers (free beta HCG,
PAPP-A), with ultrasound nuchal translucency
(NT)
- PAPP-A is lower in pregnancies complicated
with Down syndrome than in normal ones.
- HCG is higher & NT is thicker in Down
syndrome pregnancies.

Second trimester screening (Triple test)[15th – 18th gestational weeks]
A method combining measurements of 3
analytes, with maternal age into a single risk
estimate.
• AFP (alpha fetoprotein )
• uE3 (unconjugated estriol )
• HCG (Human chorionic gonadotrophin)

In Down syndrome:
- AFP & uE3 are 25% lower than expected
- HCG is two folds higher than expected

- A 4th analyte, Dimeric Inhibin A (DIA), that is
elevated in cases of Down syndrome is added
and the test is called Quadruple test

Fetal trisomy 18:
- AFP and uE3 concentrations are low
- HCG concentrations are also very low
- No role for DIA
Women who test positive (or those who test
negative but aged above 35) should be offered
amniocentesis to obtain fetal cells for
karyotyping or other DNA based techniques;
the only way to confirm Down or trisomy 18
syndromes diagnosis.

Screening for Neural tube Defects (NTD):
- Optimal screening is between 16 and 18 weeks
of gestation.
- The most commonly used AFP MoM cutoffs are
between 2.0 and 2.5 MoM.
- A second sample is needed for moderately
elevated results (2.0 to 3.0 MoM)
- If the result for the second AFP test is not
elevated, the woman is considered to be
screen-negative.

- If the result is still elevated:
• 4-D U/S is used to verify gestational age
• Identify other possible reasons for the
increased AFP (ex: multiple pregnancy,
abdominal hernias into the umbilical cord)
- Patients still having an unexplained ↑↑ AFP
test results amniocentesis for measurement
of amniotic fluid AFP and acetylcholinesterase.

- Ultrasound
diagnosis of open
neural tube defects
is now so reliable
that it is often used
for diagnosis in
women with
elevated maternal
serum AFP without
waiting for amniotic
fluid measurements.

FETAL SCREENING:
I) Amniocentesis:
- Removal of amniotic fluid containing fetal cells,
via a needle puncture from the uterus.
- Any genetic analysis can be performed on
these cells.
- Performed 14-20th week of gestation.

FETAL SCREENING:
I) Amniocentesis:
- Removal of amniotic
fluid containing fetal cells,
via a needle puncture
from the uterus.
- Any genetic analysis can
be performed on these
cells.
- Performed 14-20th week
of gestation.

Amniotic fluid testing is done for:
• Diagnosis of NTD (Confirming a screen positive
mother)
• Diagnosis of congenital diseases
• Diagnosis of Isoimmunisation disease
• Assessment of fetal lung maturity

1) Diagnosis of NTD:
AFP:
- Patients with unexplained high maternal serum
AFP levels and normal ultrasonography should
be offered amniotic fluid testing
- AFP values greater than or equal to 2.0 MoM
are considered elevated.
- A frequent interference is contamination of the
fluid with fetal blood. Elevated amniotic fluid
AFP should be tested for fetal hemoglobin, a
sensitive marker of fetal blood contamination.

Acetylcholine Estrase (AChE):
- AChE is a neural enzyme present in cerebrospinal fluid
and fetal blood.
- It is not present in maternal blood and is not normally
detectable in amniotic fluid.
- The abnormal presence of acetylcholinesterase in
amniotic fluid is suggestive of an open fetal defect.
- When AChE is detected, the ratio of AChE to
pseudocholinesterase
(PChE),
a
non-specific
cholinesterase normally found in amniotic fluid, may
help distinguish open neural tube defects from fetal
blood contaminated fluid.

2) Tests for isoimmunization disease:
- Isoimmunization disease is a fetal haemolytic
disorder caused by maternal antibodies
directed against antigens on fetal
erythrocytes.
- The amount of bilirubin in the amniotic fluid is
useful for determining the severity of the
condition.
- The most common cause of severe disease is
sensitization of Rh-negative woman to the D
antigen of the Rh system.

- An association exists between gestational age,
severity of the disease, and bilirubin
concentration.
- The concentration of bilirubin is too low to be
measured by standard photometric
techniques (up to 0.03mgldL) but the
determination can be done by absorption
spectrophotometry.
- The maximal absorbance of bilirubin is at 450
nm.

- In the absence of significant amounts
of bilirubin, the absorbance spectrum for
the amniotic fluid between 365 and 550
nm is nearly exponential.

-When plotted on a semi log scale (linear
curve), the degree to which the curve
deviates from a straight line at 450 nm is
linearly proportional to the concentration of
bilirubin (∆A 450)

- Results of (∆A 450) are established into
3 classification zones based on
gestational age “ Liley's zones”

II) CVS:
- Chorionic villi are
precursors of the placenta
and a good source of fetal
tissue.
- CVS can be performed
safely by 10th week both
transabdominally and
transvaginally

- Used for:
•Cell culture &
karyotyping
•Enzyme assays
•Direct gene analysis

III) Pre implantation
genetic diagnosis (PGD):
- For couples undergoing
IVF.
- Fertilized eggs are checked
for the gene mutation and
only the unaffected embryos
are introduced into the
uterus in the hope of a
successful implantation.
- Cells are isolated from the
blastocyst (16 – 20 cells
embryo), where DNA is
extracted and tested for
common or expected genetic
mutations.

POST NATAL NEW BORN SCREENING:
- NBS is a process of early identification of health
conditions followed by their subsequent timely
treatment before the onset of disease processes
thereby minimizing the risk of long-term
sequelae.
- Key issues considered for NBS:
• What are the effects of each genetic disorder?
• What treatment is currently available for each
genetic disorder, and at what age does treatment
begin?

• Based on demographics, how many people
are likely to be affected by each genetic
disorder?
• Should all newborn infants receive the same
screening tests? Why or why not?
• Can a test in question be performed on a large
scale in laboratories? Why or why not?
• What is the cost per test and the total for
screening?
• Will early identification of persons with the
genetic disorder lead to cost savings in
treatment or care? Why or why not?

Alpha-1-antitrypsin Deficiency:
Clinical description:
- Alpha-1-antitrypsin deficiency can lead to early
onset of emphysema and/or liver failure.
- These symptoms usually appear when a person
is in their 30’s or 40’s.
- Symptoms are more severe in smokers than in
nonsmokers.

Genetics:
- This disorder is caused by a mutation in the
proteinase inhibitor (PI) gene on chromosome 14.
- The normal protein coded for by this gene is
involved in tissue repair.
- Disorder symptoms depend on which type of
mutation an individual has in the PI gene.
- There are more than 70 different alleles of the PI
gene.
- The M allele is the wild variant. The mutant alleles
S and Z are the most common disease causing
variants.

Inheritance:
Autosomal recessive
Testing:
- This disorder can be detected by testing the
levels of alpha-1-antitrypsin in blood. If they are
abnormally low, the next step is to identify the
exact alpha-1-antitrypsin protein variants the
person carries.
- Abnormal forms of the alpha-1-antitrypsin
protein can be detected using dried blood as a
sample for gel electrophoresis.

Cystic Fibrosis:
- Cystic fibrosis is caused by mutations in the
cystic fibrosis transmembrane regulator (CFTR)
gene on chromosome 7 which codes for the
protein that controls ion transfer across cell
membranes.
- Disruption of salt transfer results in abnormal
gland secretions and dehydration due to
increased loss of salt and water during sweating.
- CF affects almost all of the glands in the body
that secrete fluid, resulting in a variety of
symptoms.

- Secretions may be thick and cause blockage in
the pancreas, intestines and lungs.
- Mucus blockage also provides places for
bacteria to multiply, increasing the probability
of infection.
- CF children show poor digestion, dehydration,
coughing and vomiting.
Molecular
analysis
has
identified
approximately 100 mutations in the CFTR
gene. Different mutations determine the
severity of symptoms seen in CF patients.

Testing:
- Mutation in the CFTR gene results in an
increase in an enzyme called trypsinogen. The
initial newborn screen tests for this enzyme
using a dried blood sample.
- There are hundreds of mutations in the
population, the most common is ∆F508.
- Testing all mutations is very difficult unless a
clinically accepted microchip technology is
available.

- Measurement of chloride content in sweat
collected after pilocarpine iontophoresis, is
still the gold standard test for diagnosing CF
Cystic Fibrosis Foundation Sweat Test2.flv

Huntington’s disease:
- Huntington’s disease is characterized by the
progressive death of certain neurons in the brain.
- Symptoms generally appear between the ages of 3540 years and include depression, mood swings,
amnesia, involuntary twitching and lack of
coordination.
- As the disease progresses, involuntary movements
increase, memory declines, and walking, speaking
and swallowing ability gradually diminish.
- Death soon follows from choking, infections or heart
failure.

Genetics:
- Huntington’s is caused by excessive repeating of
the DNA bases CAG (trinucleotide repeats) in
the huntingtin gene on chromosome 4.
- The normal number of repeats is 10 – 35,
Huntington’s disease patients have 36 - 121
repeats.
Inheritance
Autosomal dominant
Testing
The huntingtin gene is analyzed in a blood sample
to determine the number of CAG repeats.

Maple Syrup Urine Disease (MSUD)
- Individuals with maple syrup urine disease
(MSUD) are unable to properly metabolize
three amino acids: leucine, isoleucine and
valine.
- The enzymes required to process these three
amino acids are absent, inactive or only
partially active.
- Because these amino acids do not get broken
down completely, high levels accumulate in
the blood, urine and sweat.

-The by-product of isoleucine has a
characteristic sweet smell which gives the
disorder its name.
- The three amino acids and their derivatives can
be toxic at high levels and can lead to brain
injury, mental retardation, seizures, vomiting,
coma and even death.
Genetics:
The most common type is classic MSUD which is
caused by a defect in the BCKDHA gene on
chromosome 19.

Inheritance
Autosomal recessive
Testing
- Newborn screening programs that test for
MSUD use the same blood sample collected
for PKU and galactosemia tests.
- Generally, blood is analyzed for elevated levels
of leucin

Phenylketonuria (PKU)
- PKU is caused by the lack of phenylalanine
hydroxylase , an enzyme that processes the
amino acid phenylalanine.
- Phenylalanine is not broken down and
accumulates in the blood & it is toxic to the
brain.
- Untreated individuals with PKU show
progressive developmental delay in the first
year of life, mental retardation, seizures,
autistic-like behavior and a peculiar body odor.

Genetics
- In PKU individuals, the phenylalanine
hydroxylase gene on chromosome 12 is
disrupted.

Inheritance
Autosomal recessive

Testing
- The blood phenylalanine level can be measured
using a spot of dried blood.
- The PKU test (the Guthrie test) was the first
genetic screening test developed.
- Automated tests (MS / MS) are now used in some
screening programs.
- The timing of the test is important; the test should
be completed after the first day and before the
seventh day of life. If done too soon, low levels in
the newborn can be masked by the presence of
maternal phenylalanine.

Sickle Cell Disease:
- A group of inherited disorders of RBCs
- If the gene encoding hemoglobin is mutated, it
causes a change in the shape of the molecule.
- When the mutated hemoglobin delivers
oxygen to the tissues, the red blood cell
collapses, resulting in a long, flat sickle-shaped
cell. These cells clog blood flow, resulting in a
variety of symptoms including pain, increased
infections, lung blockage, kidney damage,
delayed growth and anemia

Genetics
- The gene encoding the beta chain of the
hemoglobin
molecule,
located
on
chromosome 11, can be mutated in a variety
of ways that result in different types of sickle
cell disease.
- Some mutations are more common than
others. The three most common types of
sickle cell disease are hemoglobin SS (Hb SS),
hemoglobin SC (Hb SC), and hemoglobin sickle
beta thalassemia (HbS beta-thalassemia).

Inheritance
Autosomal recessive
Testing:
- Most screening programs utilize thin-layer
isoelectric focusing (IEF) or high performance
liquid chromatography (HPLC) techniques
performed on capillary blood collected from a
heel stick and absorbed onto filter paper.

Newborn Screening Card Rejection.flv

Pediatrics clinical chemistry

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