Health Dictionary
Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.
Spinal muscular atrophy risk factor
Introduction
Editors-in-Chief: C. Michael Gibson, M.S., M.D.; Priyamvada Singh, MBBS
Overview
Overview
- ~98% of parents of an affected child are carriers. Whereas, the rest of 2% that are not carriers have denovo mutation.
- The pattern of inheritance is autosomal recessive in SMA. The risk of occurrence/recurrence if both the parents are carriers is 25%, while the risk of having an unaffected carrier child is 50%.
This means that in every pregnancy there is
- 1 chance in 4 (25% chance) that they will have a child who inherits both copies of the mutated gene. So, there will be no working gene product in the child and he/she will be affected by the condition.
- 1 chance in 4 (25% chance) that their child will inherit both copies of the working gene and will be unaffected by the condition
- 1 chance in 2 (i.e. 2 chances in 4; 50% chance) that their child will inherit the mutated gene and the working copy of the gene from each parent and he/she will be an unaffected carrier of the faulty gene, just like the parents i.e. carrier for the condition