Is Kennedy Disease hereditary?

Kennedy Disease, also known as spinal and bulbar muscular atrophy (SBMA), is a hereditary condition caused by a genetic mutation passed through families. It follows an X-linked recessive inheritance pattern, meaning the mutation is located on the X chromosome, primarily affecting biological males.

Is Kennedy Disease hereditary and how is it inherited?

Yes, Kennedy Disease is strictly hereditary. It is caused by an expansion of a CAG trinucleotide repeat in the AR (androgen receptor) gene. Because it is X-linked, biological males who inherit the mutated gene will develop Kennedy Disease. Females who carry one copy of the mutation are typically asymptomatic carriers, though they have a 50% chance of passing the gene to each of their children.

What are the risks for children of an affected parent?

The inheritance patterns for Kennedy Disease are specific to the sex of the offspring:

• If the father has Kennedy Disease: All of his daughters will be obligate carriers, but none of his sons will inherit the condition (as sons receive the Y chromosome from their father).


• If the mother is a carrier: Each son has a 50% chance of being affected by Kennedy Disease, and each daughter has a 50% chance of being a carrier.

Is genetic testing available for Kennedy Disease?

Genetic testing is the gold standard for confirming a diagnosis of Kennedy Disease. A molecular genetic test analyzes the number of CAG repeats in the AR gene; a result of 38 or more repeats is diagnostic. Because de novo (spontaneous) mutations are extremely rare in this condition, it is nearly always inherited from a parent. We strongly recommend genetic counseling for families to discuss the implications of these results and to explore options like preimplantation genetic testing (PGT) for those planning pregnancies.

Next steps

• Consult with a clinical geneticist to verify your family history and discuss testing options.


• Connect with the 9 members of the Kennedy Disease community at DiseaseMaps.org to share experiences and support.


• Contact the Kennedy's Disease Association (KDA) for disease-specific resources and research updates.

Medical disclaimer: This content is for informational purposes only and does not replace professional medical advice, diagnosis, or treatment.

References

• NIH Genetic and Rare Diseases Information Center (GARD) - Spinal and bulbar muscular atrophy


• Online Mendelian Inheritance in Man (OMIM) - #313200


• Orphanet - Spinal and bulbar muscular atrophy


• Kennedy's Disease Association (KDA)