1. NEW BORN SCREENING
PRENATAL TESTING
• DNA based diagnostic tests
• F >35 ↑ risk for development of genetic disease
1. Ultra sound – easiest to perform
2. Chromosomal analysis (karyotyping)
• i.e. suspected Trysomi 21 defect (Down’s syndrome)
• Sample of choice: amniotic fluid, chorionic villi sample (CVS)
NEONATAL SCREENING
• Primarily to detect disorders in which immediate treatment can prevent
catastrophic consequences.
• Detects mostly inborn errors of metabolism
• Routine neonatal tests chosen are based mainly on the epidemiology,
depending what chromosomal abnormalites are present or prevalent in a
given area.
• In the Philippines, according to REPUBLIC ACT 9288 there are 5
GENETIC DISEASES or INBORN ERRORS of METABOLIS that every
new born MUST be tested for:
1. Congenital Adrenal Hyperplasia (CAH)
2. Congenital Hypothyroidism (CHT)
3. Phenylketonuria (PKU
4. Galactosemia
5. G6PD Deficiency
• If a child has family Hx of a specific chromosomal abnormality, the lab
must be notified to include the specific test for that particular abnormality
in the screening process.
• Most of the neonatal screening tests are tests for metabolic disorders.
• FALSE NEGATIVE RESULTS may occur for some screening tests for
some diseases of the following diseases if specimen from newborn is
taken LESS THAN 24 hrs after birth: congenital hypothyroidism,
homocystinuria, tyrosemia, cystic firosis.
• The following tests may be performed on infants who appear clinically well
in the 1st 24 hrs but develop signs of illness on the 2nd or 3rd day:
o CBC – to test for any red cell or other hematological abnormalities
o Blood gases- to test for metabolic acidosis or alkalosis
o Urinalysis- to test for ketonuria
o Blood lactate level – to test for lactic acidosis
o Blood ammonia level
o Liver function test
o PT, PTT
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2. 1. Congenital Adrenal Hyperplasia (CAH)
• Synonym: adrogenital syndrome
• All variants are autosomal recessive.
• Most common variants: Type I and Type II
• Most common cause (95%): 21-hydroxylase deficiency
• Types I, II, and III - block formation of corticosterone, and cortisol
o Abnormally ↑ androgen hormone production
Male ♂ Female ♀
In Utero enlargement of genetalia ambiguous female
(pseudohermaphtoditism (macrogenitosomia genetalia
) praecox)
Masculization of external
gentalia
After Birth precocious puberty virilization
Atypical variants ambiguous female Unaffected
Type IV, V , and VI gentalia
• Type II, IV, and VI –
o causes a salt losing crisis similar to that seen in Addison’s disease.
o Blocks the mineralcorticoid pathway
• Methods/tests used to detect 21 hydroxylase deficiency:
o Measuring the level of 17-OHP (hydroxypregnenolone)
o Genotyping the blood of the newborn
• Tx: glucocorticoid or mineralcorticoid replacement
• Goals of Tx:
o Children: normal growth, normal height, and pubertal development
o Adult:
 lessen signs of virilization and resume fertility
 ↓ ACTH to <100 ng/L
 ↑ 17-OHP (hydroxypregnenalone) to100-1000 ng/dL
2. Congenital Hypothyroidism (CHT)
• Most common preventable cause of mental retardation.
• Early detection is critical for the prevention of the severity of mental
retardation associated with hypothyroidism.
• Untreated CHT leads to mental retardation.
• Prevalence: 1 in 3000 – 5000 births. Sometimes higher depending on the
ethnicity and/or deficiency of iodine.
o 85% - due to agenesis (failure of development of thyroid gland) – most
common cause.
o 10% - due to defect in enzymes of thyroid hormone synthesis
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3. o 95% - are PRIMARY
o 3-5% - are SECONDARY as a result of a pituitary disorder or a
malfunction of the hypothalamus
• Fetal Screening for CHT:
o Specimen used: dry blood spot on fetal screening card or cord serum
o Test for BOTH T4 and TSH.
• Result: ↓T4 and ↑TSH = HYPOTHYROIDISM
• If ONLY T4 tested - may miss compensated hypothyroidism.
• 15% of infants with a PRIMARY thyroid disorder have a
normal T4 (compensated) and an ↑TSH.
• If ONLY TSH tested – may miss hypothyroidism due to pituary disorder or
hypothalamic malfunction.
• FALSE ↓T4 may occur due to:
1. Very low birth weight (VLBW) infants
o T4 must be re-tested on 2nd and 4th-6th week for late onset of
transient hypothyroidsm.
2. Congenital absence of thyroid binding globulin (TBG)
• TSH is MORE sensitive than T4 in testing for hypothyroidism.
o LAB RESULT INTERPRETATION
• TSH = <10 meq/L – NO further action needed
• TSH = 10-20 meq/L – must repeat test in 2-6 weeks
• TSH = >20 meq/L – Dx with CHT
3. Phenylketonuria (PKU)
• It is an autosomal recessive genetic disorder.
• Characterized by a deficiency in hepatic enzyme phenylalanine
hydroxylase.
• Phenylalanine hydroxylase in needed to convert amino acid
PHENYLALANINE to amino acid TYROSINE.
• Phenylalanine hydroxylase DEFICIENCY leads to PHENYLALANINE
ACCUMULATON in the body.
• Excess PHENYLALANINE in the body is CONVERTED to
PHENYLPYRUVATE (also known as PHENYLKETONE)
• PHENYLKETONE is detected in the URINE.
• ACCUMULATION of phenylalanine in the body leads to MENTAL
RETARDATION.
• At birth, infant serum phenylalanine level = <2mg/100mg due to maternal
enzymes.
TESTING FOR PKU
1. Urine Phenyl Ketonurina Test or Ferric chloride Test
• Detected 3-6 weeks
2. Blood Test/s
• HPLC
• Guthrie Test
• Detects > 4mg/100ml
• Test for both phenylalanine and tyrosine levels
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4. • Typical (+) PKU patient:
o ↑Phenylalanine = >15mg/100mg
o ↓Trosine = <5mg/100mg
• Ideal time to collect PKU specimen = after 48hrs (24-48 hrs after infant
started breastfeeding or formula feeding)
• If specimen taken <24 hrs of birth – have baby brought back for retest
• If PKU result within normal range – have baby come back 1 to 2 weeks for
confirmatory recheck.
• Tx: low protein (especially phenylalanine) diet and avoid foods that contain
aspartame (it contains phenylalanine).
4. Galactosemia
• Autosomal recessive genetic disorder
• Unable to convert galactose to glucose
• Found in 1 out or 62,000 born infants
• Most common cause: Deficiency in galactose-1-phosphate uridyl
transferase (GALT) – causes Classic Galactosemia
o Deficiency in GALT enzyme leads to ↑ galactose accumulation in
blood
o Some symptoms: hypoglycemia, vomiting, diarrhea, irritability,
feeding difficulty, failure to thrive, jaundice, hepatomegaly, easy
bruisability, lethargy, cataract, premature ovarian failure, brain
damage, cirrhosis.
o Duarte galactosemia is a variant of classical galactosemia. Mostly
asymptomatic.
o Dx by demonstrating galactose in blood and urine
 2/3 of patients with galactosemia - test (+) for galactose
 Copper sulfate reducing test (Clinitest)
 Glucose oxidase test
• 2 Other Enzyme Deficiencies that cause Galactosemia
o Galactokinase (GALK) Deficiency
 May cause cataracts in infants
o Galactose Epimerase (GALE) Deficiency
 Also known as GALE deficiency, Galactosemia III and UDP-
galactose-4-epimerase deficiency
 There are 2 forms of epimerase deficiency: benign RBC
deficiency and Severe liver deficiency. Severe form is
similar to galactosemia
• Screening Tests:
o Pager (sp?) Assay
 Milk or formula feeding necessary to perform.
o Beutler’s Fluorometric Method
 Milk or formula feeding NOT necessary to perform.
 Does NOT detect galacto kinase deficiency but DOES detect
the Duarte galactosemia variant.
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5. • Other Lab Test to aid in Dx:
o AST and ALT (included in LFT) – liver enzymes will be ↑
o Histologically: biopsy reveals fatty metamorphosis as early as 3
months of age.
• Tx: Restriction of galactose in the diet.
5. G6PD Deficiency
• Out of the 5 components of the NBST, this is the only disorder that is X-
linked.
• Affects males more than females.
• Mostly among Caucasian with Kurdish Jewish people with the highest
Incidence.
• Also common in the Middle East, the Mediterranean, and Asia.
• G6PD is seen in the pentose phosphate pathway of the RBCs. It’s plays a
role of glucose metabolism in the RBC.
• Abnormal hemolysis in G6PD deficiency can manifest in a number of
Ways:
o Prolonged neonatal jaundice possibly leading to kernicterus
o Hemolytic crises in response to:
 Illness (especially infections)
 Certain drugs: antimalarial, sulfa drugs, nitrofurontoin, apirin,
and analgesics similar to aspirin like phenacetin.
 Certain foods: most notably fava beans (favism)
 Certain chemicals
 Diabetic ketoacidosis
o Very acute crisis can cause acute renal failure
• Dx Test:
o Peripheral Blood Smear
• Look for the following features:
o Poikilocytosis, spherocytes, and Heinz bodies.
o Heinz bodies – precipitate seen when hemoglobin is
Denatured. Special stains are used like methyl violet and
Crystal violet
o Other screening tests: Methemoglobin Test, gluthathione stability
test, dye reduction test, ascorbic acid test, fluorescent spot test,
G6PD assay.
 False normal result with African Americans: GTS and DRT.
 G6PD assay - Invalid result if patient transfused:.
6. Trisomy 21 (Down’s Syndrome)
7. Cystic Fibrosis
8. Amino Aciduria
9. Lysosomal Storage Disorder
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