Prenatal health screenings offer expecting parents insights into their baby’s development. These screenings provide valuable information, helping families and healthcare providers prepare for a baby’s needs.
What is NIPT
Non-Invasive Prenatal Testing (NIPT) is a screening test performed during pregnancy, typically after 10 weeks. It involves a simple blood draw from the pregnant individual. NIPT analyzes small fragments of cell-free DNA (cfDNA) circulating in the maternal bloodstream, which originate from both the pregnant individual and the placenta. Placental DNA usually mirrors the fetus’s genetic makeup.
NIPT primarily screens for common chromosomal conditions like Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13). It can also screen for sex chromosome aneuploidies. As a screening test, NIPT estimates the risk of a condition rather than providing a definitive diagnosis.
Understanding Spinal Muscular Atrophy
Spinal Muscular Atrophy (SMA) is a genetic neuromuscular disorder affecting motor neurons in the spinal cord. These nerve cells control voluntary muscle movement. In individuals with SMA, their loss leads to progressive muscle weakness and wasting, known as atrophy.
SMA is caused by mutations or deletions in the SMN1 (survival motor neuron 1) gene, which is essential for producing the survival motor neuron protein. SMA is inherited in an autosomal recessive pattern, meaning an individual must inherit two affected copies of the SMN1 gene, one from each parent, to develop the condition. Parents carrying one mutated copy typically do not show symptoms.
NIPT and SMA Detection
Some specialized NIPT panels can be extended to screen for specific single-gene disorders, including Spinal Muscular Atrophy. This extended NIPT looks for deletions or mutations within the SMN1 gene. It analyzes fetal cfDNA in the maternal blood sample to assess the risk of the fetus inheriting two non-functional copies of the SMN1 gene.
As with all NIPTs, NIPT for SMA is a screening test, not a diagnostic one. It provides a risk assessment, indicating an increased or decreased likelihood of SMA. While these extended NIPTs have high sensitivity for detecting common SMN1 gene deletions, they have limitations, including the possibility of false positive or false negative results. These tests typically do not determine the carrier status of the parents.
Following Up on NIPT Results
A high-risk NIPT result for SMA necessitates confirmatory diagnostic testing. These diagnostic procedures are invasive and include chorionic villus sampling (CVS) or amniocentesis. CVS is typically performed earlier in pregnancy, between 10 and 14 weeks, while amniocentesis is usually done between 16 and 20 weeks.
Genetic counseling plays an important role both before and after NIPT, particularly when considering or interpreting results related to single-gene disorders like SMA. A genetic counselor can explain the implications of the NIPT results, discuss the accuracy and limitations of the screening test, and outline the available diagnostic options. They also provide support in understanding the inheritance patterns of SMA and the potential impact on future pregnancies.