New Statistics on Carrier Frequency in North America

Neil and I are big proponents of carrier testing for SMA. We have both been tested and confirmed as carriers. Neil's (wonderful) sister, Amanda, got her results back and she is not a carrier. We are so thrilled for her and her husband, Philip. As I like to say, "Currently, prevention is the only cure."

It used to be estimated that carrier rate was between 1 in 40 and 1 in 60. However, a recent post on the Families of SMA website revealed more accurate statistics for North Americans.

Genzyme Genetics Publishes a Paper Showing Carrier Rates for Spinal Muscular Atrophy.

July 27, 2009.

The paper entitled "Differences in SMN1 allele frequencies among ethnic groups within North America" indicates that although there is a carrier rate between 1 in 25 and 1 in 50 in the general population, this can differ significantly among ethnic groups.

SMA is considered to be a pan-ethnic disease. However, carrier frequencies for many ethnicities, including most ethnic groups in North America, are unknown. To provide an accurate assessment of SMN1 mutation carrier frequencies in African American, Ashkenazi Jewish, Asian, Caucasian, and Hispanic populations, more than 1,000 specimens in each ethnic group were tested using a clinically validated, quantitative real-time PCR assay that measures exon 7 copy number.

The observed one-copy genotype frequency was 1 in 37 (2.7%) in Caucasian, 1 in 46 (2.2%) in Ashkenazi Jewish, 1 in 56 (1.8%) in Asian, 1 in 91 (1.1%) in African American, and 1 in 125 (0.8%) in Hispanic specimens. Additionally, an unusually high frequency of alleles with multiple copies of SMN1 was identified in the African American group (27% compared to 3.3% - 8.1%). This latter finding has clinical implications for providing accurate adjusted genetic risk assessments to the African American population.

The implications of this work are most significant for Hispanic patients who carry lower risks of SMN1 mutations and for African American patients who bear increased frequencies of two-copy alleles. These data will facilitate the accurate interpretation of clinical testing results and provide additional information for genetic counseling.

Differences in the frequency of SMA carriers were significant among several ethnic groups. This study provides an accurate assessment of allele frequencies and estimates of adjusted genetic risk that were previously unavailable to clinicians and patients considering testing.

Click here to read the full journal article.

When Neil and I were seeing a fertility specialist to get pregnant with Oliver, we were encouraged to get carrier testing for Cystic Fibrosis. But not for Spinal Muscular Atrophy.