Study Notes: Rare Diseases

General Science July 28, 2025 5 min read

1. Definition and Overview

Rare diseases are medical conditions that affect a small percentage of the population.
In the United States, a disease is considered rare if it affects fewer than 200,000 people.
In Europe, the threshold is 1 in 2,000 people.
There are over 7,000 identified rare diseases, with new ones discovered each year.
Most rare diseases are genetic, often present at birth, but some can appear later in life.

Ancient records: Early descriptions of rare diseases can be found in ancient Greek, Roman, and Egyptian texts.
19th century: Physicians began systematically documenting unusual medical cases, leading to the identification of rare genetic disorders such as hemophilia.
20th century: The rise of genetics and biochemistry enabled scientists to link specific genes to rare diseases.
1983 Orphan Drug Act (USA): Passed to encourage pharmaceutical companies to develop treatments for rare diseases, called “orphan drugs,” by offering incentives like tax credits and market exclusivity.

Researchers identified mutations in the CFTR gene as the cause of cystic fibrosis, a rare genetic disorder.
This discovery enabled genetic testing and targeted research for treatments.

Developed in the 1990s for diseases like Gaucher disease and Fabry disease.
ERT involves replacing missing or defective enzymes in patients, significantly improving quality of life.

CRISPR-Cas9 technology allows precise editing of genes.
Early experiments have shown promise in correcting genetic mutations responsible for rare diseases like sickle cell anemia and Duchenne muscular dystrophy.

Genetic sequencing helps doctors tailor treatments to the specific mutations causing a patient’s rare disease.
Example: Spinal muscular atrophy (SMA) treatments now target the exact genetic defect.

Many countries have expanded newborn screening programs to detect rare diseases early, allowing for prompt intervention.

International databases collect information about rare disease patients to accelerate research and improve diagnosis.

Gene therapy, RNA-based drugs, and stem cell treatments are being developed for rare diseases previously considered untreatable.

Orphan drugs are often extremely expensive, sometimes costing hundreds of thousands of dollars per year.
Debate exists over whether pharmaceutical companies are exploiting incentives for profit.

Many rare disease patients struggle to access specialized care, especially in low-income countries.
Some treatments are only available in clinical trials or certain countries.

Critics argue that funding is disproportionately allocated to rare diseases compared to common illnesses, given the small number of patients affected.

Myth: “Rare diseases are always inherited and only affect children.”

Fact:

While many rare diseases are genetic, some are caused by infections, environmental factors, or unknown causes.
Rare diseases can affect people of any age, including adults. Examples include rare cancers and autoimmune disorders.

Some rare diseases are linked to environmental exposures, such as toxins, chemicals, or pollutants.
Example: Exposure to certain industrial chemicals has been associated with rare neurological conditions.
The discovery of plastic pollution in the deepest parts of the ocean (Jamieson et al., 2020) raises concerns about the long-term health effects of microplastics on humans, potentially contributing to rare diseases through bioaccumulation and disruption of biological processes.
Environmental changes can also influence the emergence of rare infectious diseases by altering ecosystems and animal habitats.

Reference: Jamieson, A.J., et al. (2020). “Microplastics and synthetic particles ingested by deep-sea amphipods in six of the deepest marine ecosystems on Earth.” Royal Society Open Science.
- This study found microplastics in deep-sea organisms, raising concerns about the unknown health effects on humans, including potential links to rare diseases.
Gene therapy advances: In 2022, the FDA approved the first gene therapy for beta-thalassemia, a rare blood disorder, marking a significant step forward in rare disease treatment.

Rare diseases are conditions affecting a small fraction of the population, most often caused by genetic mutations but sometimes linked to environmental factors or infections.
Historical milestones include the identification of genetic causes, development of enzyme replacement therapies, and the passage of the Orphan Drug Act.
Modern advances such as gene editing, personalized medicine, and newborn screening have improved diagnosis and treatment options.
Controversies remain around drug pricing, access, and research funding.
Environmental factors, including pollution, may contribute to the development of rare diseases, as highlighted by recent findings of microplastics in the ocean.
Ongoing research and international collaboration are critical for improving outcomes for rare disease patients.

Rare diseases are diverse, often serious, and can affect anyone.
Scientific advances are leading to better understanding and new treatments.
Environmental health is increasingly recognized as a factor in rare disease emergence.
Awareness, funding, and equitable access to care are ongoing challenges.