The PSEN2 gene encodes the presenilin 2 protein, a critical component of the gamma-secretase complex, which is involved in the processing of amyloid precursor protein (APP) and Notch receptors. Below, I provide a detailed overview of the requested information about the PSEN2 gene.

### 1. Associated Genes
The PSEN2 gene is associated with several other genes involved in Alzheimer's disease and related pathways:

- **PSEN1 (Presenilin 1)**: Another member of the presenilin family, often implicated in familial Alzheimer's disease.
- **APP (Amyloid Precursor Protein)**: The substrate for gamma-secretase, which, when improperly processed, contributes to amyloid plaque formation in Alzheimer's.
- **NOTCH (Notch Receptor)**: A family of receptors involved in cell signaling processes and development, which are also cleaved by gamma-secretase.
- **APOE (Apolipoprotein E)**: While not directly associated with PSEN2, the ε4 allele of APOE is a major genetic risk factor for Alzheimer's and interacts with amyloid processing pathways.
- **MAPT (Microtubule-Affinity Regulating Protein Tau)**: Tau pathology is linked to Alzheimer’s disease and may interact with the pathways involving presenilins.

### 2. Aging and Age-Related Diseases
The PSEN2 gene is significantly involved in Alzheimer's disease (AD), a major age-related neurodegenerative disorder. Specific details include:

- **Alzheimer's Disease**: Mutations in PSEN2 are linked to early-onset forms of Alzheimer's. The PSEN2 gene contributes to the accumulation of amyloid-beta, a central element in the pathogenesis of AD.
- **Aging**: As individuals age, the processing of APP and the metabolism of amyloid-beta can become dysregulated, leading to neurodegenerative changes and cognitive decline, often implicated in the progression of Alzheimer's disease.

### 3. Drug Interactions
Several classes of drugs interact with the gamma-secretase complex, which includes the presenilin proteins. Notable examples include:

- **Gamma-secretase inhibitors**: These drugs are developed to inhibit the activity of gamma-secretase to reduce amyloid-beta production as a therapeutic approach in Alzheimer’s disease. Examples include semagacestat and avagacestat.
- **APP cleavage modulators**: These can also affect the function and processing of proteins associated with PSEN2.

### 4. Pathways and Biological Processes
PSEN2 is involved in various biological pathways, including:

- **Gamma-secretase signaling**: The enzyme complex cleaves substrates such as APP and Notch, playing pivotal roles in cellular signaling pathways.
- **Calcium signaling**: PSEN2 is implicated in calcium homeostasis and intracellular signaling by functioning as a calcium-leak channel.
- **Cellular processes**: It is involved in pathways regulating gene expression, protein processing, and mitochondrial-ER communication, impacting overall cellular health and function.

### Summary
The PSEN2 gene plays a crucial role in the development of Alzheimer's disease and is involved in key pathways related to protein cleavage and calcium signaling. It interacts with other genes that are essential for understanding neurodegeneration. The relationship between PSEN2 mutations and age-related diseases highlights its importance in cognitive decline. Various drug classes targeting gamma-secretase are of interest for therapeutic purposes.