States Where Rare Genetic Diseases Are Most Common

Rare genetic disorders affect an estimated 25–30 million Americans (National Organization for Rare Disorders), yet their prevalence varies widely across states. Factors such as ethnic heritage, population isolation, and healthcare access influence which states see the highest rates of rare genomic diseases. From Pennsylvania’s Amish communities to Louisiana’s Cajun populations, let’s explore which states have the high concentrations of certain rare conditions—and why.

1. Pennsylvania – The Amish and Founder Effects

Pennsylvania’s Old Order Amish and Mennonite populations have elevated rates of several rare recessive disorders due to the founder effect—a phenomenon where a small, isolated population leads to a higher frequency of inherited mutations. One example is Maple Syrup Urine Disease (MSUD), which occurs in about 1 in 380 births among Old Order Mennonites, compared to roughly 1 in 185,000 in the general U.S. population (University of Pennsylvania). Similarly, pyruvate kinase deficiency, a rare blood disorder, is seen at abnormally high rates in Belleville, PA, where it accounts for 10% of all known cases worldwide (Genetics in Medicine).

2. Louisiana – Rare Genetic Disorders in Cajun Communities

Louisiana’s Cajun population, descended from a small group of French settlers, exhibits a unique genetic signature that has led to an increased prevalence of rare diseases (Louisiana State University). Among them is Friedreich’s ataxia, a rare neurodegenerative disease that affects about 1 in 20,000 Cajun individuals—significantly higher than the 1 in 50,000 national rate (National Ataxia Foundation). Another condition, Usher syndrome, which causes progressive blindness and deafness, is so prevalent that screening programs specifically target Louisiana's Cajun communities (National Organization for Rare Disorders).

3. New York – A Hotspot for Ashkenazi Jewish Genetic Disorders

New York’s large Ashkenazi Jewish population means it has one of the highest rates of inherited conditions such as Gaucher disease, Tay-Sachs, and Canavan disease (Mount Sinai Genetic Testing Laboratory). For example, Gaucher disease occurs in about 1 in 450 people of Ashkenazi descent, compared to the much rarer occurrence in other populations (National Gaucher Foundation). Similarly, BRCA1/2 gene mutations, which increase the risk of breast and ovarian cancer, are 1 in 40 among Ashkenazi Jews—about 10 times more common than in the general population (BreastCancer.org).

Additionally, New York has the second-highest number of people with sickle cell disease in the U.S., with over 11,700 cases due to its large African-American and Afro-Caribbean populations (Sickle Cell Disease Association of America).

4. Florida – A High Burden of Sickle Cell and Genetic Disorders

Florida leads the nation in sickle cell disease cases, with an estimated 13,900 people living with the condition (CDC Sickle Cell Data Collection Program). The state's diverse population, including a significant African-American and Afro-Caribbean community, contributes to this high burden. Additionally, South Florida’s large Ashkenazi Jewish population means higher rates of Tay-Sachs and Gaucher disease, similar to New York (Genetic Disease Foundation).

Florida’s population also skews older than average, meaning it has higher diagnoses of adult-onset rare diseases like Huntington’s disease and hereditary neurological disorders (Huntington’s Disease Society of America).

5. Arizona – Rare Genetic Diseases in Native American Communities

Arizona and neighboring New Mexico are home to large Navajo and Apache (Athabaskan) populations, which have uniquely high rates of inherited diseases due to historical genetic bottlenecks (National Institutes of Health). For instance, Navajo neurohepatopathy, a severe genetic disorder affecting the nervous system and liver, is seen at 1 in 2,520 live births among the Navajo, a far higher rate than the general population (Genetics in Medicine).

Similarly, Athabaskan Severe Combined Immunodeficiency (SCID), a fatal immune disorder, occurs almost exclusively in the Navajo and Apache peoples at rates 100 times higher than in non-Native populations (NIH Genetic Studies). Arizona’s geographic isolation and historical migration patterns have played a major role in concentrating these genetic disorders within these communities.

Why Certain States Have More Rare Genetic Diseases

Patterns in rare genetic disease prevalence are often linked to:

• Founder Effects & Isolation: Small populations with limited genetic diversity lead to higher rates of recessive diseases, as seen in the Amish (PA), Cajuns (LA), and Navajo (AZ).

• Ethnic & Ancestral Factors: Genetic conditions are more common in certain ethnic groups, such as sickle cell in African-Americans (FL, NY), Gaucher in Ashkenazi Jews (NY, FL), and Tay-Sachs in Cajuns (LA).

• Healthcare Access & Screening Programs: States with advanced medical centers (NY, FL, PA) tend to detect more cases, boosting reported prevalence.

• Environmental & Social Influences: Geographic isolation (e.g., the Navajo in AZ) can exacerbate genetic bottlenecks, while migration patterns shape where conditions concentrate (e.g., Florida’s Caribbean-born sickle cell patients).

Final Thoughts

The concentration of rare genetic diseases in certain states underscores the deep connection between genetics, ancestry, and geography. By understanding these trends, states can better tailor genetic screening, research, and treatment efforts to the populations most affected.

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