What Is the ALMS1 Gene? Plain-Language Guide

The ALMS1 gene was first identified in 2002, more than 40 years after Alström Syndrome was first described. Knowing the gene tells us a lot about why the syndrome looks the way it does — why it affects so many body systems, why some symptoms appear earlier than others, and where new treatments might one day target. This article explains the gene in plain language without assuming a science background.

A gene is an instruction in the DNA inside almost every cell. Each gene tells the cell how to build one specific protein. Proteins are the workhorses of the body — they form structures, send signals, do chemistry. Most genetic conditions happen when a change in a gene means the protein doesn't get built properly.

Humans have around 20,000 genes. Each is identified by a name (often capital letters and numbers) and a location on a specific chromosome.¹

ALMS1 is on chromosome 2 — one of the 23 pairs of chromosomes humans have. Specifically, it sits at a location called 2p13.1.

The gene contains 23 exons (the parts that actually code for the protein). When the gene is read, the cell uses those exons to build the ALMS1 protein, which is unusually large — about 4,169 amino acids long.²

The ALMS1 protein lives in two specific structures inside cells:

The basal body of primary cilia

Most cells have a tiny antenna-like structure called a primary cilium. Cilia stick out from the cell surface and sense signals from the environment — light, hormones, fluid flow, mechanical pressure. They're crucial during development and throughout life.

The base of each cilium is anchored by a structure called the basal body. ALMS1 protein lives in the basal body and is essential for cilia to form and work properly.³

The centrosome

The centrosome is the cell's microtubule-organizing center — the structure that organizes the cell's internal scaffolding and helps direct cell division. ALMS1 also functions here.

When ALMS1 protein is missing or doesn't work, cilia and centrosomes don't function properly, and many cellular processes downstream are disrupted.

Primary cilia exist on most cells in the body. They're especially important in:

• The retina — photoreceptor cells use specialized cilia called connecting cilia to function
• The cochlea — sensory hair cells in the inner ear depend on cilia-related signaling
• The heart muscle — cilia play roles in heart development and function
• The kidney — cilia in tubular cells sense urine flow and help maintain kidney health
• The hypothalamus — neurons regulating hunger and energy balance use cilia
• Adipose tissue — fat cells signal through cilia
• The pancreas — beta cells use cilia in regulating insulin signaling

When ALMS1 doesn't make a working protein, cilia in all these tissues are affected. That's why Alström Syndrome looks like a multisystem condition rather than affecting just one organ.

This category of genetic disorders is called ciliopathies. Other ciliopathies include Bardet-Biedl Syndrome, polycystic kidney disease, Joubert Syndrome, and some forms of Usher Syndrome.

A person with Alström Syndrome has two altered copies of ALMS1 — one from each parent. The most common changes are:

• Nonsense mutations (about 47% of variants in a recent large study) — turn a "build" instruction into a "stop" instruction, truncating the protein⁴
• Frameshift mutations (about 45%) — small insertions or deletions that scramble the reading frame downstream
• Splice-site mutations (about 3%) — disrupt how the gene's exons are joined
• Missense mutations (about 2%) — change one amino acid; sometimes disrupt the protein's folding
• Larger deletions or duplications (rare) — bigger structural changes

Most disease-causing changes cluster in three regions of the gene — exons 8, 10, and 16. This is why most diagnostic tests focus on these areas first.

A "carrier" has one altered ALMS1 copy and one normal copy. The normal copy makes enough functional protein to keep cells working — so carriers don't have Alström features and don't typically experience health problems related to ALMS1.

A person is "affected" only when both copies of ALMS1 are altered. We cover this further in How Is Alström Syndrome Inherited?.

The 2002 discovery of ALMS1 changed Alström care:

• Diagnosis can be confirmed by a blood test rather than relying solely on clinical features
• Family members can have carrier testing
• Prenatal and pre-pregnancy testing become possible
• Specific research targets open up — without a known gene, drug or gene-therapy development is essentially impossible

The flip side: Alström is harder to develop gene therapy for than some conditions. Most gene-therapy approaches use viral vectors that have a size limit; ALMS1 is so large that fitting it inside the most common vectors is technically challenging. Researchers are exploring workarounds.

• Alström Syndrome Genetics: ALMS1 Gene Explained (Pillar)
• How Is Alström Syndrome Inherited?
• Are Both Parents Carriers? Understanding ALMS1 Carrier Status
• ALMS1 Mutations: Understanding Your Genetic Test Report
• The Genetics of Alström Syndrome for Healthcare Providers

April 30, 2026.