Spinal muscular atrophy (SMA)

Spinal muscular atrophy (SMA) is a rare inherited neurogenetic condition which affects the motor nerves in the spinal cord (motor neurons), causing muscle weakness. Babies may look healthy at birth, but as motor nerves are lost, the muscles become weak, causing difficulties with motor development, breathing and swallowing.   

SMA is caused by a mutation in both copies of the SMN1 gene.  It is caused by a missing or faulty gene called the SMN1 gene.  Babies usually received two copies of this gene – one from each parent.  A person with only one functioning SMN1 gene, is referred to as a “carrier” of SMA and is completely healthy. So healthy parents may pass down the missing or faulty copy without knowing.  A baby born with SMA has received the missing or faulty SMN1 gene copy from both parents.   

There are several different types of SMA. SMA type 1 develops in the first 6 months of life. These babies may have breathing problems and difficulty feeding and swallowing. Without treatment this is a very severe condition which causes death in the first 2 years of life.  Children with type 2 and type 3 SMA usually present after 6 months of age with low muscle tone and weakness, which affects the ability to sit or walk.  

SMA is rare. It affects 1 in 10000 babies, so we expect screening to pick up about 6 affected babies across New Zealand each year.

While the incidence is SMA is low, it is a very severe condition with considerable impact on families and health services.   

Disease modifying treatments are now available for SMA. All treatment trials have demonstrated that early treatment, before the onset of symptoms, results in the best health outcomes for infants. Treatment can slow and in some cases even stop the progression of SMA, offering affected children a healthy life without significant muscle weakness.  

The screening laboratory will perform the test for SMA on the same blood spot card as used for the other screened disorders. 

The screening test for SMA involves taking a punch from the dried blood spot and testing for absence of any copies of the SMN1 gene. The test is not able to detect healthy carriers of SMA.  

Blood spot specimen collection will not change from the current procedure. 

Notification of results will be as for other disorders screened for on the bloodspot card. Medical consultants will be available to assist with all abnormal SMA screening results. The screen positive infant will be reviewed by a paediatrician or paediatric neurologist to collect a confirmatory venous blood sample for further genetic testing. Treatment options will then be discussed by a Paediatric Neurologist. 

Inclusion of screening for SMA within the NMSP has been comprehensively assessed and was endorsed by the National Screening Advisory Committee.  

The Antenatal and Childhood Screening team of the National Public Health Service (NPHS) initially received a request from paediatric neurologists to consider the addition of testing for SMA. The NMSP Policy Framework has a rigorous process for assessing nominations for new disorders for screening. Expert advisors to the NPHS (including paediatricians, laboratory scientists, geneticists, economists) reviewed New Zealand cases, international practice, literature, and cost-effectiveness. Views of relevant consumer groups were sought. 

The decision to add testing for SMA to the NMSP is in line with a number of countries that are considering or have started SMA screening. SMA is tested for in most states in the USA and is being implemented across Australia. 

The exact start date of screening for SMA is still being worked through and this information will be updated when a start date has been set.

Newborn Metabolic screening resources