WHAT IS NEWBORN SCREENING ?Newborn screening is a public health programdesigned to screen infants shortly after birthfor a list of conditions that are treatable butnot clinically evident in newborn period.
WHAT FOR NEWBORN SCREENING ?• “The goal of newborn screening is earlydetection of children at increased risk forselected metabolic or genetic diseases so thatmedical treatment can be promptly initiatedto avert metabolic crises and preventirreversible neurological and developmentalsequelae.”
HISTORY OF NEW BORN SCREENING• 1930’s George Jervis at NY identified 50 clientswith metal retardation attributed to PKU• 1963 Robert Guthrie, microbiologist-pediatrician at State University of New Yorkdevised simple inexpensive which allowedscreening for PKU• 1965 New York State law for newbornscreening, Public Health Law 2500
• 1970 -1980s: congenitalhypothyroidism, congenital adrenalhyperplasia, galactosemia• 1990s:DNA tests used as second tier – SickleCell Disease screening, Cystic Fibrosisscreening• 2000s : Tandem Mass Spectrometer (MS/MS)Many diseases, one test
CARDINAL PRINCIPLES OF SCREENING• The disorder has a relatively high incidence so that thecost per diagnosed individual is reasonable• An effective and not overly expensive treatment isavailable.• A relatively inexpensive screening test that is suitablefor high volume testing (preferably automatable)• The screening test has a very high sensitivity (very lowfalse negatives) and high specificity (low false positiveswhich require expensive follow-up)
CRITERIA FOR NEWBORN SCREENING• Disorder produces irreversible damage beforeonset of symptoms• Treatment is effective if begun early• Natural history of disorder is known
SCREENING PROCEDURE• SPECIMEN COLLECTIONBlood specimen is obtained from heel of infantIt should be obtained from medial or lateral sideof the heel
TIMING OF COLLECTION• Normal Term Newborn: Before nurserydischarge or 3rd day of life whichever is earlier.• Preterm or LBW: 2 wks of age or at dischargewhichever is earlier.• Newborn who is to receive blood transfusion,One specimen collected before transfusion &second specimen 2 days after transfusion.
SCREENING TESTS• BACTERIAL ASSAYS:Punching of small disc from Guthrie specimenDisc are place in agar or silica gel & containbacteria growth media & other necessary factorsEach bacterial plate are specified for response to aparticular metabolite.The amount of growth around the disc is directlyproportional to the concentration of metabolite inblood.They are used to screen for amino acid disorders.
Tandem Mass Spectrometry (MS/MS) HighImpact and High Throughput• One disease, one test is not cost-effective• Many diseases, one test is cost-effective• MS/MS allows for rapid, simultaneous analysisand detection of many disorders of aminoacid, organic acid, and fatty acid metabolism• Sample set up determines which masses andtherefore which compounds are detected• 2 minute analysis time• Automated data processing for results
MS/MS Methodology – continuedCompounds analyzed are amino acids andacylcarnitines–Amino acids – to identifyPKU, MSUD, homocystinuria–Acylcarnitine – carnitine (vehicle) + fattyacid for identification of organic aciduriasand fatty acid oxidation disorders
SECONDARY TEST• An abnormal finding on newborn screeningtest is not diagnostic of a disorder.• Additional tests should be performed tosubstantiate the original finding.• Also the original specimen is retested for theanalyte that is abnormal.
• In screening for congenital hypothyroidism,Low T4TSH ImmunoassayLow TSH Normal TSHCongenital Transient low T4Hypothyroidism
DISORDERS MOST COMMONLYSCREENED• PHENYLKETONURIA• CONGENITAL HYPOTHYROIDISM• GALACTOSEMIA• HOMOCYSTINURIA• MAPLE SYRUP URINE DISEASE• CONGENITAL ADRENAL HYPERPLASIA• SICKLE CELL DISEASE
PHENYLKETONURIA• INCIDENCE: 1 IN 12000 live births• Untreated: Mental retardation & neurologicalabnormalities• Screening is done by MS/MS• Screening test is positive if phenylalanine levelis > 6mg/dl• Liver disease, Galactosemia & Tyrosinemiatype 1 can also produce phenylalanine levels.
CONGENITAL HYPOTHYROIDISM• INCIDENCE: 1 in 3000 to 5000 newborn• UNTREATED: Growth retardation & delayedcognitive development• Two Screening approaches are usedPrimary screening for low T4 with secondaryscreening for high TSHPrimary screening for high TSH
• FALSE POSITIVELow T4: Premature infants, Thyroxin bindingglobulin deficiencyHigh TSH: Perinatal stress• FALSE NEGATIVENormal T4: In first 24hrs of life.Normal TSH: In premature infants with CH it maytake 2 or more wks for TSH elevation to develop
GALACTOSEMIA• INCIDENCE: 1 in 62000• MANIFESTATIONS: Failure tothrive, vomiting, Liver disease & death fromsepsis due to E.Coli• 2 Screening TestSPECIFIC ENZYME ASSAYMeasures activity of Galactose 1 Phosphate UridylTransferraseIdentifies only galactosemia
METABOLITE ASSAY Measures total Galactose(galactose & galactose 1phosphate)Identifies other galactose metabolic disorders likeGalactokinase & Epimerase deficiencyPOSITIVE SCREENING TESTRAPID CONFIRMATORY TESTTESTING OF URINE FOR REDUCING SUBSTANCES
URINE CONTAINS REDUCING SUBSTANCESDISCONTINUATION OF BREAST OR FORMULA FEEDSSUBSTITUTION WITH NON LACTOSE FORMULA Eg, SOYENZYME ASSAY FOR RBC GALT ACTIVITY
HOMOCYSTINURIA• INCIDENCE: 1 IN 344,000 births• UNTREATED: Ectopia lentis, OsteoporosisThromboembolism, Mental Retardation• SCREENING MARKER: Plasma Methioninelevels.• MS/MS is used for screening
• Isolated Hypermethioninemia may occur inMAT Deficiency,Tyrosinemia type 1Liver disease• HOMOCYSTINURIAHomocysteine is detectable in plasma & urinePlasma total Homocysteine & MethioninePlasma cysteine is reduced
• ISOLATED HYPERMETHIONINEMIAPlasma Methione markedlyNo detectable homocysteine in plasma or urineNormal plasma cysteine levels
MAPLE SYRUP URINE DISEASE• INCIDENCE: 1 IN 185,000 births• FULMINANT DISEASE: SevereKetoacidosis, Vomiting & lethargy & mayprogress to coma & death• SCREENING MARKER: 4 fold elevation ofplama leucine in NB
• Confirmatory plasma & urine specimensobtained• Plasma shows marked increase in leucine,isoleucine & valine (branched chain aminoacids)• Urine is strongly positive for ketones• Maple syrup odor appears earliest in cerumen& later in urine. Can be detected by cottontipped swab inserted into infant’s ear.
• CONGENITAL ADRENAL HYPERPLASIAScreening Marker: Increased levels of 17OHP• SICKLE CELL DISEASEScreening is by means of Hemoglobinelectrophoresis.It also identifies sickle cell trait & other abnormalhemoglobins.
OTHER DISORDERS DETECTED BYNEWBORN SCREENING• BIOTINIDASE DEFICIENCY• OTHER AMINO ACID DISORDERS: EgCitrullinemia• LONG CHAIN & MEDIUM CHAIN ACYL CoADEHYDROGENASE DEFICIENCY• CYSTIC FIBROSIS• NEUROBLASTOMA