The RNU4-90P gene is a processed pseudogene that is part of the small nucleolar RNA (snoRNA) family, specifically classified as a member of the U4 snoRNA family which is involved in the modification and processing of ribosomal RNA (rRNA). Processed pseudogenes typically arise from the reverse transcription of mRNA and subsequent integration into the genome, which means they may not have a direct functional role in the same manner as protein-coding genes. 

### 1. Associated Genes:
Research into processed pseudogenes often reveals associations with other snoRNA-related genes. In the case of RNU4-90P, while direct associations aren't commonly highlighted, it may be related to other small nucleolar RNA genes, such as:

- RNU4-1 (a functional U4 snoRNA)
- Other RNU4 family members like RNU4-6 and RNU4-8

These relationships primarily stem from its classification as a small nucleolar RNA and common origin within RNA gene families.

### 2. Aging and Age-Related Diseases:
The specific links between RNU4-90P and aging or age-related diseases are not well-documented. However, pseudogenes, particularly those related to snoRNAs, may play indirect roles in cellular processes that are impacted by aging, such as RNA processing and metabolism. Disruption in the snoRNA function has been associated with ribosome biogenesis and could influence age-related conditions or cancer, but specific studies on RNU4-90P in the context of aging are scant.

### 3. Drug Interactions:
Currently, there are no specific drugs or drug classes that are well-documented as interacting or having a therapeutic target effect related to RNU4-90P. Since it is a pseudogene, it is unlikely to have direct drug interactions. Most attention in pharmacogenetics tends to focus on functional genes, particularly those coding for proteins involved in drug metabolism and efficacy.

### 4. Pathways and Biological Processes:
RNU4-90P is mainly involved in the following pathways and biological processes:

- **Ribosome biogenesis**: As a member of the snoRNA family, it is implicated in the modification and assembly of rRNA, essential for ribosome function.
- **Small nucleolar RNA (snoRNA) function**: The primary role of snoRNAs, including RNU4-90P, revolves around guiding chemical modifications of other RNAs, mainly rRNA, through methylation and pseudouridylation.
- **RNA modification**: It contributes indirectly to the maturation of rRNA, facilitated by the actions of other functional snoRNAs in the cellular environment.

Overall, while RNU4-90P itself does not encode a protein and is categorized as a pseudogene, its family context within small nucleolar RNAs reveals its possible involvement in critical cellular processes, particularly concerning ribosome function and RNA processing. However, further research would be pivotal in exploring its specific roles or implications in health and disease.