Age-related penetrance is the expression of the mutated phenotype being dependent upon the individual’s age. Often such disorders showcase their effects when the individual ages. Amyotrophic lateral sclerosis(AMLS) and frontotemporal dementia (FTD) are said to be two disorders that fully develop when one is an adult.

please read these 2 post and expand on each post with more information finding another sources.
direct copying or quoting (even with citations) will be considered plagiarism.
POST 1:
Age-related penetrance is the expression of the mutated phenotype being dependent upon the individual’s age. Often such disorders showcase their effects when the individual ages. Amyotrophic lateral sclerosis(AMLS) and frontotemporal dementia (FTD) are said to be two disorders that fully develop when one is an adult. AMLS is a progressive neurodegenerative disease that causes the loss of muscle control as it affects the nerve cells within the brain and spinal cord. While FTD is a type of dementia that is rather uncommon and causes issues with language and behavior. While dementia is a blanket term used to describe mental issues due to gradual changes and brain damage over the years, AMLS affects the frontal and temporal lobes located on the front and sides of the brain. It is due to the pathogenic hexanucleotide repeat expansion found within the C9orf72 gene. This mutation is said to have both age-related as well as incomplete penetrance, as the majority of individuals that are afflicted are above their 50s, while some have made it to their 90s without displaying the phenotypes associated with both diseases. Research has shown, however, that the median age of symptoms onset to those carrying C9orf72 mutations is 58, while penetrance was relatively completed at 83 years of age. Additionally, males have a higher likelihood of developing either disorder young, if they possess the mutation as compared to their female counterparts.

References:

NHS Choices, NHS, https://www.nhs.uk/conditions/frontotemporal-dementia/#:~:text=Frontotemporal%20dementia%20is%20an%20uncommon,the%20frontal%20and%20temporal%20lobes).

Amyotrophic Lateral Sclerosis (ALS). Mayo Clinic, Mayo Foundation for Medical Education and Research, 13 Oct. 2022, https://www.mayoclinic.org/diseases-conditions/amyotrophic-lateral-sclerosis/symptoms-causes/syc-20354022.

Murphy, Natalie A., et al. Age-Related Penetrance of the C9ORF72 Repeat Expansion. Nature News, Nature Publishing Group, 18 May 2017, https://www.nature.com/articles/s41598-017-02364-1.

POST 2:

I would like to add a response to the first question you posed about other diseases with age-related penetrance. Late-onset Parkinsons disease has been shown to be caused by multiple point mutations in various genes including LRRK2, EIF4G1, VPS35, and DNAJC13 as well as duplications or triplications in the SNCA gene [1]. Penetrance for this disease varies by the specific gene, its mutation and by ethnicity [1]. In the article I read, it discussed that the LRK2 gene, in particular has been studied for its various point mutations and the related penetrance of the disease. For instance, the LRK2 p.N1437H has an upper quartile age of 50 years or older while the LRK2 p.Y1699C has an upper quartile age of 56 years or older [1]. The differences in the penetrance of Parkinsons disease are likely due to the type of substitution and its functional consequence. The different mutations affect the interactions including binding partners as well as signaling pathways downstream which ultimately affects expression of the proteins leading to disease [1].

Reference: [1] https://jamanetwork.com/journals/jamaneurology/fullarticle/1917547

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