Standard Carrier Screening (4 Genes)


Related Gene(s): CFTR, DHCR7, FMR1, SMN1

The standard pan-ethnic panel is a basic carrier screening panel that tests for cystic fibrosis (CF), fragile X syndrome, Smith-Lemli-Opitz syndrome (SLOS), and spinal muscular atrophy (SMA).

CF is an autosomal recessive disease caused by pathogenic variants in the CFTR gene. It can result in the production of unusually thick mucus, which primarily affects breathing, digestion, and reproduction. CF is a chronic and progressive disease, for which there is no cure. This carrier screen is performed by sequencing and targeted genotyping analyses.

Fragile X syndrome is the most common inherited form of mental retardation. It is caused by a change in the FMR1 gene on the X chromosome, so is inherited in an X-linked manner. Within the FMR1 gene, there is a region of repeating DNA bases referred to by the letters CGG. The number of CGG repeats present within the FMR1 gene determines if an individual has fragile X syndrome or is at risk to have a child with fragile X syndrome.

SLOS is a disorder involving cholesterol metabolism. Some features of SLOS include growth retardation, microcephaly (small head circumference), moderate-to-severe intellectual disability, behavior problems, and physical malformations like distinctive facial features, cleft palate, cardiac defects, underdeveloped external genitalia in males, and finger/toe abnormalities. The gene associated with SLOS is DHCR7. Like CF, this carrier screen is performed by sequencing and targeted genotyping analyses.

SMA is a disease that results in severe and progressive weakness of the voluntary muscles affecting breathing, swallowing, head and neck control, crawling, and walking. SMA is an autosomal recessive condition caused by a deletion and/or pathogenic variant in both copies of the SMN1 gene. Carrier testing for SMA is performed in two ways. First, genetic testing to determine the number of SMN1 gene copies present in an individual is carried out. This method can detect ~90-94% of SMA carriers. The second method of testing is by analysis for a genetic marker (g.27134T>G) that is oftentimes found on chromosomes that have 2 copies of SMN1 gene copies, which modifies the residual risk of being a silent carrier.

Although this testing can detect the majority of disease-causing pathogenic variants, a negative result does not eliminate the possibility that an individual is a carrier of a rare pathogenic variant that was not identified. Please refer to the residual risk table to determine the risk following a negative result.

For prenatal samples, please contact our laboratory at 800-298-6470 for more information.


Specimen Requirements

  • Blood: Two 5-10 mL EDTA tubes (lavender top)
  • Saliva: Saliva specimens are accepted in Oragene DNA (OG-500) kits by DNA Genotek. Please note that Tay Sachs enzyme analysis cannot be performed on saliva
  • If carrier screening was previously performed through Sema4, reanalysis and/or test enhancements may be ordered without providing an additional specimen. Please contact the laboratory to determine if an additional specimen is required

Ordering Information

Shipping

  • Ship at room temperature

Turnaround Time

  • 10-14 days from receipt of specimen


Resources

Expanded Carrier Screen patient brochure
Expanded Carrier Screen provider brochure
Carrier screening clinical information sheet
Prenatal test requisition, including carrier screening and Noninvasive Prenatal Select