Is there a disease that only one person has?

September 21, 2025 •

4 min read

While the idea of a disease afflicting only one person seems like something from science fiction, the reality is that ultra-rare conditions do exist, especially in the field of genetics. Thanks to advances in genetic sequencing, it is now possible to confirm that a disease is so unique that it affects only a single known individual at the time of diagnosis, effectively answering the question, is there a disease that only one person has?.

Quick Summary

Yes, it is possible for a disease to affect only one known person, particularly due to a unique genetic mutation. Though a patient might be the first or only documented case, medical research often reveals that others share a similar, or identical, genetic variant, evolving the understanding of these ultra-rare conditions over time.

Key Points

Single-Person Diseases Exist Initially: Yes, it is possible for a disease to affect only one known person, particularly due to a spontaneous, de novo genetic mutation.
Diagnosis Drives Discovery: When a unique condition is identified in one individual (the index case), modern genomic sequencing allows researchers to pinpoint the genetic cause.
Medical Community Takes Note: Publishing these findings in medical literature alerts the global scientific community, which can lead to the identification of other patients with the same genetic mutation over time.
Evolving from 'Unique' to 'Ultra-Rare': What starts as a one-person disease often transitions into an ultra-rare disorder as more cases are discovered, allowing for greater understanding and the formation of patient communities.
Genetic Research is Crucial: Advances in genomic technology have drastically reduced the time it takes to diagnose these conditions, turning long diagnostic odysseys into more manageable journeys for affected families.

The concept of a one-person disease

The idea of a disease that affects only one person—known in the medical community as an 'index case' when they are the first to be documented—is fascinating yet deeply challenging for those involved. This phenomenon is almost exclusively found within the realm of genetic disorders, where a specific, and often de novo (new), mutation occurs spontaneously during the formation of an egg or sperm, or very early in embryonic development. Unlike inherited conditions passed down through generations, a de novo mutation is not present in either parent's genetic makeup. This can create a unique set of symptoms and biological functions that have never been observed before in any other human.

Documenting and naming the ultra-rare

When a patient presents with a mysterious set of symptoms, doctors embark on a diagnostic odyssey. Advances in genomic sequencing have dramatically accelerated this process. Previously, it might have taken years to find the root cause, if it were ever found. With whole-exome and whole-genome sequencing, researchers can now analyze a patient's entire genetic code to pinpoint the exact mutation responsible. For diseases with just one known patient, a formal name is often not immediately available, and the condition might be referred to by the mutated gene (e.g., NGLY1 deficiency) or even the patient's name, at least informally.

Case studies of initially unique conditions

Several real-world examples illustrate this concept:

NGLY1 Deficiency: The case of Bertrand Might, the first patient diagnosed with a mutation in the NGLY1 gene, is a classic example. Initially, he was the only one known to lack the N-glycanase 1 protein. His diagnosis led to the identification of other children with the same condition, ultimately forming the basis for a patient foundation and research.
CDG-GET4: A young patient named Damian Omler was diagnosed with a new type of Congenital Disorder of Glycosylation (CDG), termed CDG-GET4. For a time, he was the only known individual with this specific variant of the disease.
ACOX1 Gene Mutation: A Missouri teen named Mitchell Herndon had a disease so rare that it didn't have a name. His condition, a mutation of the ACOX1 gene, was shared by only one other known person at the time of diagnosis.

These examples show that while a patient may initially be the only one with a specific disease, research and information sharing can lead to the discovery of other cases, shifting the condition from a 'one-person disease' to an 'ultra-rare disease'.

The evolution from 'one-of-a-kind' to 'ultra-rare'

What often starts as a 'disease that only one person has' often evolves into a recognized, albeit ultra-rare, disorder. This transition is enabled by modern genomic analysis and global collaboration. When a new mutation is identified, it is typically published in medical literature and recorded in genetic databases, allowing other researchers and clinicians to identify patients with similar or identical mutations. The path to becoming an officially recognized disorder involves several key steps:

Identification of an Index Case: A patient presents with a new, never-before-seen constellation of symptoms.
Genetic Analysis: Genomic sequencing identifies a unique de novo mutation responsible for the condition.
Medical Publication: The findings are published, documenting the link between the gene mutation and the clinical symptoms.
Global Search and Identification: The medical community becomes aware of the specific genetic signature, and similar cases may be identified elsewhere in the world.
Formation of a Patient Group: Families with affected individuals connect, often through social media or patient foundations, to share resources and support.

This process is how a single, isolated case can grow into a community of patients, providing comfort, understanding, and hope for future research and treatments.

The crucial role of patient advocacy

For those with ultra-rare diseases, patient advocacy is vital. Groups like the National Organization for Rare Disorders (NORD) play a crucial role in providing resources, promoting research, and connecting families affected by these conditions. The journey for these individuals and their families often involves navigating the complexities of a condition with little to no prior medical understanding. Patient advocates help to raise awareness, secure funding for research, and ultimately drive the scientific community toward finding treatments.

Comparison: Single-Gene vs. Multifactorial Disorders

To understand the nuances of a 'one-person' disease, it is helpful to compare it with other types of genetic disorders.


Feature	Single-Gene Disorder (e.g., NGLY1 deficiency)	Multifactorial Disorder (e.g., Autism, Heart Disease)
Genetic Cause	A single mutation in one gene, often de novo.	Multiple genes interacting with environmental factors.
Inheritance Pattern	Can be inherited (dominant/recessive) or new (de novo).	No clear inheritance pattern; complex interplay.
Prevalence	Often extremely rare; can start as a single known case.	Relatively common, affecting many people globally.
Diagnosis	Relies on finding a specific mutation via genetic testing.	Diagnosis is based on a collection of symptoms and clinical criteria.
Medical Research	Focused on understanding the function of a single protein and correcting its defect.	Broad focus on identifying multiple genetic risk factors and environmental triggers.

The diagnostic challenges and future outlook

Despite advances in genomics, diagnosis remains a significant challenge for many. The journey can be long and frustrating, a period often called a 'diagnostic odyssey'. The hope for a patient with a potentially unique disease lies in the continued advancement of genetic research and data sharing among scientists and clinicians worldwide. As our ability to sequence and analyze the human genome becomes more affordable and widespread, the speed at which these ultra-rare conditions are identified and understood will increase. This not only offers answers to families who have been searching for years but also contributes valuable insights into general human biology and health.

For more information on the wide spectrum of genetic disorders, the Centers for Disease Control and Prevention provides comprehensive resources on their website: https://www.cdc.gov/genomics-and-health/about/genetic-disorders.html.

Frequently Asked Questions

A 'one-person disease' is a condition, typically genetic, that is so rare that only one person is known to have it at the time of discovery. The patient is known as the index case, and the disease is often caused by a unique genetic mutation not inherited from either parent.

A genetic mutation can affect only one person if it is a de novo mutation. This means the genetic change occurs spontaneously in the egg, sperm, or very early embryo, and is not present in the genetic makeup of the parents. This results in a unique condition never seen before in that family's history.

Rarely. While a patient may be the first and only documented case initially, the publication of the genetic cause often leads to the discovery of other individuals with the same or similar condition. It then becomes an ultra-rare, rather than a one-person, disease.

A 'diagnostic odyssey' refers to the long and difficult process many patients with rare diseases experience before receiving an accurate diagnosis. Symptoms may be misattributed to more common conditions, and it can take years to pinpoint the correct cause, especially if it's an ultra-rare genetic disorder.

The naming of an ultra-rare disease can vary. Initially, it might be referred to by the mutated gene (e.g., NGLY1 deficiency) or an acronym. Historically, some diseases were named after the physician who discovered them (eponyms), but this practice has changed. Often, the name evolves as more is learned about the underlying biology.

Patient advocacy is critical for people with ultra-rare diseases. Organizations and patient groups help connect families, share information, and raise awareness and funding for research. Their efforts accelerate discovery and support the affected community.

While most true 'one-person diseases' are genetic, it is theoretically possible for an extremely rare combination of environmental exposures and genetic predisposition to cause a unique set of symptoms in one individual. However, the vast majority of such documented cases are due to a single, unique genetic mutation.