Spinal Muscular Atrophy Carrier Screening (SMA)

SMA carrier status detection via SMN1 copy number analysis

5 business daysMLPA + SequencingBlood sample

What is this test?

Spinal Muscular Atrophy (SMA) is one of the most common severe autosomal recessive conditions, affecting approximately 1 in 10,000 births. It causes progressive muscle weakness and, in its most severe form (Type I), is the leading genetic cause of infant death. SMA is caused by deletions or mutations in the SMN1 gene. Approximately 1 in 40-50 people is a silent carrier. This test determines your SMN1 copy number to identify carrier status — allowing at-risk couples to plan ahead.

Key Benefits

Prevents the Leading Genetic Cause of Infant Death

SMA Type I is the most common genetic cause of death in children under 2. Identifying carrier couples allows prevention through PGT-M or prenatal diagnosis.

High Carrier Frequency

About 1 in 40-50 people is an SMA carrier regardless of ethnicity — making this one of the highest-yield carrier tests available.

Fast Results

5-day turnaround provides timely information for reproductive planning.

Treatment Available If Detected Early

If both partners are carriers and pregnancy occurs, early SMA detection in utero enables access to gene therapy treatments that can be transformative when started before symptom onset.

How It Works

Blood Draw

A simple blood sample is collected. No fasting or special preparation required.

DNA Extraction

DNA is isolated from white blood cells for molecular analysis.

MLPA Analysis

Multiplex Ligation-dependent Probe Amplification (MLPA) precisely determines the number of copies of the SMN1 gene, distinguishing between 0, 1, 2, and 3+ copies.

Supplementary Sequencing

When indicated, additional sequencing is performed to detect point mutations in SMN1 that would not be identified by copy number analysis alone.

Results & Counseling

Results report SMN1 copy number and carrier status. One copy of SMN1 indicates carrier status. Genetic counseling is available to discuss reproductive implications and SMN2 copy number significance.

Who should consider this test?

All individuals or couples planning pregnancy (ACOG recommends SMA carrier screening for all)
Those with a family history of SMA or neuromuscular disease
Couples undergoing IVF who want comprehensive carrier information
Individuals from any ethnic background (SMA carrier frequency is similar across populations)

Conditions Screened

Spinal Muscular Atrophy Type I (Werdnig-Hoffmann disease — most severe, onset <6 months)SMA Type II (intermediate, onset 6-18 months)SMA Type III (Kugelberg-Welander disease — milder, onset >18 months)SMA Type IV (adult-onset, mildest form)

Accuracy & Clinical Evidence

Test Accuracy

MLPA detects approximately 95% of SMA carriers by identifying individuals with one copy of SMN1 (instead of the normal two copies). The remaining ~5% of carriers have two copies on one chromosome and zero on the other (2+0 configuration), which cannot be detected by copy number analysis alone.

ACOG recommends that SMA carrier screening be offered to all patients who are considering pregnancy or are currently pregnant. Carrier frequency is approximately 1 in 40-50 across all ethnic groups. Population-based carrier screening programs have been shown to reduce SMA births by identifying at-risk couples before conception.

For Healthcare Providers

SMA carrier screening uses Multiplex Ligation-dependent Probe Amplification (MLPA) to quantify SMN1 exon 7 copy number. Individuals with one copy of SMN1 are classified as carriers (~95% carrier detection rate). The 2+0 genotype (two copies on one chromosome, zero on the other) cannot be detected by MLPA and represents a residual carrier risk of approximately 1 in 600 after a 2-copy result. SMN2 copy number is reported when relevant, as it modifies disease severity. Point mutation analysis of SMN1 is available as a reflex test.

Important Limitations

MLPA cannot detect the rare 2+0 SMN1 configuration (~5% of carriers), resulting in a residual carrier risk even with a two-copy result.
SMN2 copy number influences disease severity but is not a precise predictor of clinical outcome.
SMA carrier screening does not detect all forms of neuromuscular disease — only SMN1-related SMA.
De novo mutations in SMN1 can occur but are very rare and cannot be predicted by carrier screening.