### HRH4 Gene Overview

**Gene Symbol**: HRH4  
**Full Name**: Histamine Receptor H4  
**Location**: Chromosome 18q11.2  
**Gene Type**: Protein-coding  

### 1. Associated Genes
The HRH4 gene may not have a direct list of associated genes specified in general summaries; however, its interactions with various genes involved in inflammatory responses and allergic reactions can be inferred. Some of the genes associated with histamine signaling, inflammation, and allergy include:

- **IL4** (Interleukin 4)
- **IL13** (Interleukin 13) 
- **TNF** (Tumor Necrosis Factor)
- **CCL2** (C-C Motif Chemokine Ligand 2)
- **CD4** (Cluster of Differentiation 4)

### 2. Aging and Age-Related Diseases
While specific studies on HRH4 concerning aging are limited, histamine pathways are known to be involved in immune responses that become dysregulated with age. Alterations in histamine receptor signaling have been linked to:

- **Chronic Inflammatory Diseases**: Such as rheumatoid arthritis, where HRH4 may play a role in modulating inflammation.
- **Neurodegenerative Diseases**: Some evidence suggests that histamine and its receptors may influence conditions such as Alzheimer's disease due to their roles in neurotransmission and neuroinflammation.

Additionally, there's an emerging interest in the role of histamine receptors in metabolic syndromes, which can be more prevalent in older populations.

### 3. Drug Interactions
HRH4 interacts with certain drug classes, particularly antihistamines and possibly drugs targeting autoimmune and inflammatory conditions. Notable drug classes include:

- **H4 Antagonists**: These are drugs specifically designed to block the effects of histamine at the HRH4 receptor and have potential therapeutic applications in allergies and inflammatory diseases.
- **Corticosteroids**: Often used in inflammatory conditions that may also involve histamine pathways.
- **Immunomodulators**: Drugs that can affect immune response may also interact with HRH4 activity indirectly.

### 4. Pathways and Biological Processes
HRH4 is involved in several important biological pathways and processes:

- **Histamine signaling pathway**: This includes the pathways that mediate functions related to inflammation and allergic responses.
- **Cytokine-cytokine receptor interaction**: Indicating its role in local immune responses.
- **Chemokine signaling pathway**: Relevant in recruiting immune cells during inflammation/allergy.
- **Regulation of immune response**: In the context of hematopoietic cells, HRH4 function refers to its involvement in altering the activity and proliferation of immune cells.

In summary, HRH4 plays a significant role in mediating histamine-related physiological responses, especially in inflammation and allergy, with associations to various related genes and potential implications in aging and disease states. Further investigation may elucidate more specific roles and therapeutic targets related to this receptor.