Newborn Screening for Disorders
Every year 4.1 million newborns in the US are screened for congenital disorders. Of these, 4,000 infants are diagnosed as suffering from a genetic disease. Statistics estimate another 1,000 infants suffering from other conditions still remain undetected.
Screening of newborn disorders by blood test is done before discharge (usually day 5) and physical examination/imaging for developmental defects is done within 72 hours and repeated at 4-6 weeks just to be safe.
- The screening tests at birth offered as routine may vary in different countries and between different hospitals across any country. Parents may request additional tests or decline specific tests in the panel
- The screening of disorders by blood tests are usually done on day 5 of birth and for non-blood testing the screening is performed within 72 hours of birth
- Most inherited and developmental disorders included in newborn screening should be diagnosed early and treatment should be initiated if possible, otherwise they can lead to severe complications
Evolution of Newborn Screening Over Time
Screening for phenylketonuria (PKU) in the US began in the 1960s using a relatively simple diagnostic method. With advances in diagnostic technology more disorders were added when methods to use blood spots became available and applicable to large populations at cheap cost. By the 1990s, numerous new metabolic disorders had been added to the screening panel.
In a 2005 report of the American College of Medical Genetics (ACMG) newborn screening for disorders termed core panel was recommended with disorders falling under the following main categories
- Blood cell disorders - sickle cell anemia and others
- Inborn errors of amino acid metabolism – Phenylketonuria and others
- Inborn errors of organic acid metabolism – Methyl malonic aciduria and others
- Inborn errors of fatty acid metabolism - Long-chain hydroxyacyl-CoA dehydrogenase deficiency (LCHAD) and others
- Miscellaneous multisystem disorders – Cystic fibrosis, congenital hypothyroidism, congenital adrenal hyperplasia, biotinidase deficiency, classic galactosemia, severe combined immunodeficiency (SCID)
- Screening for conditions not using blood tests – Congenital deafness, congenital heart defects
There are also additional conditions that may be detected by screening listed as "secondary targets" by the 2005 ACMG report. Many of these conditions are rare and unfamiliar to primary healthcare professionals and pediatricians.
Testing Newborn Infants - Key Role of Child Specialist
- The child specialist/neonatologist plays a key role in the education of parents about the availability of newborn screening tests, the advantages of early diagnosis of disorders by screening and future risks for newborn infants who do not receive screening. The child specialist explains the process of screening and follow-up to parents as well as obtaining informed consent if applicable.
- The pediatrician should be aware of factors that might influence the results of a specific screening test, such as gestational age (eg prematurity), diet, transfusions, and total parenteral nutrition (nutrition through drip via vein)
- Since these conditions require lifelong followup, the pediatrician works closely with specialized laboratories that perform these tests, and making treatment decisions as appropriate to ensure the most favorable outcome for the child and its family
Genetic counselingand testing of family members for carrier state and prenatal diagnosis of future pregnancies, may be provided if necessary in certain cases.
Common Disorders for Which Newborns Should be Screened
The following discussion will cover the most common newborn disorders that many hospitals offer for routine screening. There are many more disorders and in fact some states in the US offer as many as 50 screening tests. The incidence described is for the US population although may vary for other populations.
Screening Using Blood Tests (Blood Spot Testing)
Parents of newborn babies are given the option of testing for inherited metabolic conditions by testing a blood spot taken from the baby (often referred to as the "heel prick" and earlier termed "Guthrie" test) at 5-8 days of life (ideally on day 5). For many of these disorders early detection can be critical.
- Disorder of amino acid metabolism
- Incidence 1 in 25000
- Newer diagnostic methods include chromatography, fluorometry or mass spectrometry
- Newborn screening permits early initiation of the phenylalanine-restricted diet, overcoming the severe neurological handicap associated with untreated PKU (from 80-90% to 6-8%)
- Endocrine disorder (low thyroid hormone/thyroxine) that affects several systems
- Incidence > 1 in 5000
- Babies born before 32 weeks of gestation will need a repeat testing. The repeat test should be done at 28 days of postnatal age (taking the original expected date of birth as day 0)
- Screening is very useful as a preventable cause of growth retardation and mental handicap by early replacement of thyroid hormone
- Incidence > 1 in 5,000; among African-Americans 1 in 400
- Abnormal hemoglobin that causes anemia
- Early diagnosis can lead to a decrease in sickle cell disease associated complications such as stroke
- Incidence > 1 in 5000 (carrier state may be much lesser)
- Initial screening identifies elevated levels of immunoreactive trypsinogen (IRT), which is then followed by DNA analysis
- Neonatal screening has significantly reduced the age at diagnosis. However, the screening may miss come cases and diagnosis has to be considered even if screening test is negative
- Early diagnosis results in better management of respiratory infections, providing good nutrition and supplements, and giving psychological support
- Incidence < 1 in 100000 (much higher in Ireland)
- Disorder of sulphur containing amino acid homocysteine
- Affected babies appear normal at birth but get severe complications during childhood such as seizures, mental handicap, eye problems and vascular complications
- Early diagnosis and pyridoxine supplementation or following a low sulphur diet reduces these complications
- Incidence approximately 1 in 185,000 births worldwide (can be as high as 1 in 180 births in certain communities eg Mennonite settlements in the USA)
- Progressive neurological deterioration due to accumulation of leucine, isoleucine and valine and their corresponding ketoacids
- Brain damage is irreversible if not diagnosed and treated early in life
- Incidence > 1 in 25,000 births
- Dip in blood glucose levels and sudden death due to fasting or episodes of vomiting
- Diagnosis of the condition early (before onset of symptoms), and avoiding fasting significantly improves outcome
- Incidence between 1/40,000 and 1/60,000 in Western countries
- Lack of enzyme needed to process galactose, a sugar found in milk and dairy products
- Complications include failure to thrive, early cataracts, progressive liver disease and mental handicap
- Development of early cataracts and other complications in affected babies is fully preventable by early diagnosis and treating with a galactose (milk and dairy products) restricted diet
Screening by Physical Examination (Not Blood Test)
Certain congenital conditions are diagnosed by physical examination performed within 72 hours and additional investigations as appropriate
- Incidence > 1 in 5000
- Screened for by audiological evaluation
- Early diagnosis of hearing loss by newborn screening, has been shown to have better language development compared to unscreened children who receive a clinical diagnosis of hearing loss later
- Incidence 2 per 1000 births
- Critical CHD includes 12 structural heart defects that prevent normal pumping of blood by heart and low oxygen saturations in blood
- Low oxygen saturation detected by non-invasive pulse oximetry and if CHD is suspected, additional tests can be performed to confirm diagnosis
- Early diagnosis and correction of heart defects surgically or as appropriate significantly improves the outcome for these children
Other congenital disorders that can be screened for at birth include congenital cataract, undescended testes and developmental dysplasia of hip.
Screening for Newborn Disorders - Status and Guidelines in India
Newborn screening in India is not yet well established. Only a few private hospitals and centers in major cities such as Delhi and Mumbai perform these tests. Therefore, parents opting for these tests have to bear the extra financial burden of these tests which are usually expensive. Sadly, there are no government funded newborn screening centers or programs at present.
Parents can discuss with their doctors and based on their genetic and family history decide what screening tests to go for. The tests have to be performed as early as possible preferably within a week to enable early diagnosis and treatment.
However in a bid to change the existing situation, the Indian Academy of Pediatrics headed by Dr Sachidananda Kamath has proposed a set of newborn screening tests that can be done from the Indian perspective. These include congenital hypothyroidism (see above), hearing loss, glucose-6-phosphate dehydrogenase (G-6PD) deficiency resulting in severe anemia due to destruction of red blood cells and congenital adrenal hyperplasia (CAH) resulting in ambiguous external genitalia, fertility issues and other health problems affecting growth and development.
Due to the high costs of these tests and the differing prevalence of newborn conditions in different parts of the country, the screening tests can be further categorized as follows
Category A (must for all newborns)
- Hearing loss
- Congenital hypothyroidism
- Addition of CAH and G-6PD deficiency gradually in a phased manner
- Inclusion of sickle cell anemia and similar hemoglobin disorders in areas of high incidence
- Consanguinity for example, marriage between first cousins, niece/uncle etc with increased risk of genetic diseases
- History of having a child with unexplained seizure disorder or intellectual disability
- History of death of a child for which no cause was found
Newborns that are very sick and show clinical features to suggest a possible genetic disorder
For well to do parents and in centers particularly in major cities having the latest facilities for newborn screening, testing for 30-40 inherited metabolic disorders can be offered.
As per WHO recommendations, genetic testing should be introduced in countries that have an infant mortality rate (IMR) lower than 50. With an IMR of 40, India should start performing newborn screening and genetic testing for early diagnosis and treatment as well as preventing serious complications later. The Indian Academy of Pediatrics strongly recommends that screening of newborn disorders be included in the government’s public health program and has also offered technical and other assistance for introduction of the same.
- List of disorders included in newborn screening programs - (https://en.wikipedia.org/wiki/List_of_disorders_included_in_newborn_screening_programs#Core_panel)
- CDC Grand Rounds: Newborn Screening for Hearing Loss and Critical Congenital Heart Disease - (https://www.cdc.gov/mmwr/volumes/66/wr/mm6633a4.htm)
- Introduction to the Newborn Screening Fact Sheets - (http://pediatrics.aappublications.org/content/118/3/1304.full)
- Newborn Screening in India - (http://medind.nic.in/ibv/t15/i5/ibvt15i5p373.pdf)