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SI

Your Alpha-1 genotype is SI. This is a rare Alpha-1 genotype. While you do not have the most severe form of AATD, based on a limited amount of literature, the SI genotype may be associated with an increased risk of developing lung disease. We would stress that not all individuals with this genotype develop lung disease. An increased risk for liver disease has not been associated with this genotype. The S mutation causes a moderate reduction in the quantity of alpha-1 antitrypsin (AAT) in the blood and may be risk-raising when combined with a second AATD mutation. The I mutation results in a reduced quantity of Alpha-1 protein in the blood and may be risk-raising when combined with another Alpha-1 mutation. This result should be interpreted in the context of AAT level and clinical symptoms. More information about this genotype may be known in the future. A list of Alpha-1 specialists can be found at www.alpha1.org.

Because Alpha-1 is a genetic condition, your result means that your relatives are at increased risk to have AATD or carry abnormal alpha-1 genes. We encourage you to make your family members and any reproductive partner aware of the condition in your family and the availability of testing. Testing for relatives must look for the S and I mutations to ensure accurate results.

Alpha-1 at MUSC – Genetic Counseling

I: Likely S-like

  • Moderate deficiency allele
  • Not known to accumulate in the liver
What is Your Phenotype and What Does it Mean? – Kimberly Foil, MS, CGC, Genetic Counseling Program, Alpha-1 Foundation; Division of Pulmonary and Critical Care Medicine, Medical University of South Carolina (MUSC)

S: mild variant
• more common than the Z allele
• doesn’t get trapped in the liver – not typically associated with liver disease
• originated in the Iberian Peninsula (Spain and Portugal)
• low estimate that 5% (possibly as high as 12%) of North Americans are MS

What is Your Phenotype and What Does it Mean? – Kimberly Foil, MS, CGC, Genetic Counseling Program, Alpha-1 Foundation; Division of PulmonaryMedical term referring to the lungs. and Critical Care Medicine, Medical University of South Carolina (MUSC)