Chromosome 17: Key Genes, Mutations, and Disorders

Chromosome 17 carries the second-highest density of protein-coding genes among all human chromosomes, and that crowded genetic landscape translates directly into an outsized role in human disease. Genes on this chromosome are linked to hereditary cancers, neurodegenerative conditions, rare developmental syndromes, nerve-damaging neuropathies, and metabolic storage diseases. The chromosome is also unusually prone to structural rearrangements, which means pieces of it get deleted, duplicated, or flipped more often than on most other chromosomes, giving rise to a cluster of syndromes that are unique to this part of the genome.

A Uniquely Crowded Stretch of DNA

Chromosome 17 is a medium-sized chromosome, yet it punches well above its weight in gene content. Sequencing studies have confirmed it has the second-highest gene density of any human chromosome and ranks third among the autosomes in the density of segmental duplications, which are large, near-identical blocks of DNA that sit in multiple locations along the chromosome.¹ Those duplications matter because they act as hotspots for misalignment during cell division. When chromosomes pair up and swap segments, near-identical blocks can line up incorrectly, leading to deletions, duplications, or inversions. This architectural quirk explains why chromosome 17 is home to a disproportionate share of “genomic disorders,” conditions caused not by a single-letter mutation in a gene but by the loss or gain of a whole stretch of DNA.

Another distinctive feature is that chromosome 17 maps almost entirely to a single mouse chromosome, mouse chromosome 11. That one-to-one relationship is unusual among human autosomes and has made mouse models for chromosome 17 disorders comparatively straightforward to build, which is part of why many of the genes described below have been studied so thoroughly.

Cancer Genes That Get the Most Attention

No discussion of chromosome 17 can avoid its cancer genes. Several of the most clinically important tumor suppressors and oncogenes in all of human genetics sit here, and mutations in them collectively account for a significant fraction of hereditary and sporadic cancers.

TP53 and Li-Fraumeni Syndrome

The TP53 gene, located on the short arm of chromosome 17, encodes the protein p53, often called the “guardian of the genome” because it coordinates the cell’s response to DNA damage. When p53 works properly, it can halt cell division to allow repairs or trigger cell death if the damage is too severe. When both copies of TP53 are lost or mutated, cells accumulate mutations unchecked, which is why TP53 is the single most commonly altered gene across all human cancers.

Inheriting one defective copy of TP53 causes Li-Fraumeni syndrome, a hereditary cancer predisposition disorder in which people develop cancers in diverse tissues, often at unusually young ages. Germline TP53 mutations are found in about three-quarters of patients with the classic form of the syndrome, and the lifetime risk of developing cancer approaches 75 percent in men and nearly 100 percent in women.² One question researchers have explored is whether the remaining normal copy of TP53 is always lost in the tumors that form. In a study of 36 tumors from Li-Fraumeni patients, the wild-type copy was lost in under half of cases, and the pattern varied depending on which specific TP53 mutation the patient carried.³ That finding suggests some TP53 mutations can drive cancer even when the other copy of the gene is still intact, complicating the classic “two-hit” model of tumor suppression.

BRCA1 and Hereditary Breast and Ovarian Cancer

BRCA1 sits on the long arm of chromosome 17 and encodes a protein involved in repairing double-strand DNA breaks, one of the most dangerous forms of DNA damage. BRCA1 also participates in cell cycle checkpoints, protein modification, and chromatin remodeling, all pathways that help keep the genome stable.⁴ When BRCA1 is mutated, cells lose a critical repair pathway, which dramatically raises the risk of breast and ovarian cancer. BRCA1 mutations are among the most widely tested genetic variants in clinical oncology, and carriers are offered intensive screening and risk-reducing options including preventive surgery.

HER2 (ERBB2) in Breast Cancer Treatment

The HER2 gene, formally called ERBB2, also resides on chromosome 17 and encodes a receptor protein on the cell surface that promotes cell growth. In roughly 15 to 20 percent of breast cancers, the HER2 gene is amplified, meaning extra copies drive the cell to produce excess HER2 protein. Targeted drugs such as trastuzumab were designed specifically for these tumors, and determining HER2 status is now a routine part of breast cancer diagnosis.⁵

There is a clinically important wrinkle, though. Some tumors test positive for HER2 gene amplification but do not actually overexpress the HER2 protein. One explanation is that the amplified region of chromosome 17 is incomplete and does not include everything needed for full protein production. Patients whose tumors fall into this category are unlikely to benefit from HER2-targeted therapy, which is why testing typically involves both genetic and protein-level assays.⁶

NF1 and Neurofibromatosis Type 1

The NF1 gene encodes a protein called neurofibromin, which acts as a brake on RAS signaling, a major growth-promoting pathway in cells. Neurofibromin accelerates the breakdown of active RAS, keeping cell proliferation in check. When NF1 is mutated, that brake is lost, RAS activity rises, and cells tend to grow uncontrollably.⁷ The result is neurofibromatosis type 1, one of the most common single-gene disorders in humans, affecting roughly 1 in 3,000 people. Symptoms include café-au-lait spots on the skin, benign nerve sheath tumors called neurofibromas, and an elevated risk of certain malignant cancers. The NF1 gene itself is flanked by segmental duplications that make it susceptible to large deletions, and patients who carry these whole-gene deletions rather than point mutations tend to have more severe disease.⁸

Microdeletion and Microduplication Syndromes

Because chromosome 17 is loaded with segmental duplications, it is a breeding ground for copy-number disorders. In these conditions, a small segment of the chromosome is either missing (microdeletion) or present in an extra copy (microduplication), and the clinical picture depends on which genes are included in the affected region.

Smith-Magenis Syndrome and Potocki-Lupski Syndrome

Smith-Magenis syndrome is caused by a deletion in the 17p11.2 region that typically spans several genes, including the retinoic acid-induced 1 gene (RAI1). In some patients, a point mutation in RAI1 alone is enough to cause the syndrome, confirming RAI1 as the main driver.⁹ Features include intellectual disability, sleep disturbances tied to an inverted melatonin rhythm, self-injurious behavior, and a characteristic facial appearance. Potocki-Lupski syndrome is essentially the mirror image: a duplication of roughly the same 17p11.2 region. The critical duplicated interval spans about 1.3 megabases and includes RAI1 among 14 genes.¹⁰ Potocki-Lupski syndrome tends to produce milder intellectual disability, autism-spectrum features, and cardiovascular anomalies. The fact that deleting and duplicating the same stretch of DNA produce distinct syndromes illustrates how sensitive cells are to gene dosage.

Koolen-de Vries Syndrome

At 17q21.31, a microdeletion or a loss-of-function mutation in the KANSL1 gene causes Koolen-de Vries syndrome. The condition is characterized by low muscle tone in infancy, developmental delay, moderate intellectual disability, and a recognizable set of facial features.¹¹ Researchers have compared patients who carry the full microdeletion with those who have only a KANSL1 mutation and found no clinically meaningful difference in severity, confirming that loss of KANSL1 alone is sufficient to produce the full phenotype.¹² The 17q21.31 region is also notable because it harbors a common inversion polymorphism: roughly 20 percent of Europeans carry a roughly 900-kilobase inversion of this region, and carriers of the inverted arrangement are at higher risk of producing offspring with the microdeletion.

Miller-Dieker Syndrome

On the opposite end of chromosome 17’s short arm, at 17p13.3, deletions of the PAFAH1B1 gene (also known as LIS1) cause lissencephaly, a severe brain malformation in which the normal folds of the cerebral cortex fail to develop because neurons cannot migrate to their proper positions during fetal development. When the deletion extends further to include the neighboring YWHAE gene, the result is Miller-Dieker syndrome, which combines a more severe grade of lissencephaly with distinctive facial features and growth restriction.¹³ Children with Miller-Dieker syndrome experience profound neurocognitive impairment, seizures, and feeding difficulties, and life expectancy is significantly shortened.¹⁴

Peripheral Nerve Disease and a Metabolic Storage Disorder

Chromosome 17 also hosts genes whose disruption damages peripheral nerves or blocks a critical metabolic enzyme, producing disorders that are very different from the cancer and developmental syndromes above.

PMP22 and Charcot-Marie-Tooth Disease Type 1A

The PMP22 gene encodes peripheral myelin protein 22, a component of the insulating sheath around peripheral nerves. A duplication of a 1.5-megabase region on 17p11.2 that includes PMP22 causes Charcot-Marie-Tooth disease type 1A (CMT1A), the most common inherited peripheral neuropathy. The reciprocal deletion of the same region causes hereditary neuropathy with liability to pressure palsies (HNPP), a milder condition in which brief nerve compressions produce prolonged weakness or numbness.¹⁵ Quantitative studies of nerve tissue from patients with each condition confirmed that PMP22 protein levels are increased in CMT1A and reduced in HNPP compared with normal tissue, establishing that both diseases result from an imbalance in PMP22 expression rather than a change in the protein’s structure.¹⁶ This makes PMP22-related neuropathies a textbook example of gene dosage disease: having three copies is too much, having one copy is too little, and the nerve sheath suffers either way.

GAA and Pompe Disease

The GAA gene, located at 17q25.2-q25.3, encodes the enzyme acid alpha-glucosidase, which breaks down glycogen inside lysosomes. Mutations that reduce or eliminate this enzyme’s activity cause Pompe disease, a lysosomal storage disorder in which glycogen accumulates in cardiac, skeletal, and smooth muscle cells.¹⁷ The infantile-onset form is the most severe, presenting with massive heart enlargement and muscle weakness in the first months of life. Later-onset forms progress more slowly, primarily affecting skeletal and respiratory muscles. To date, hundreds of different mutations across the GAA gene have been cataloged, reflecting the diversity of clinical severity.¹⁸ Pompe disease was one of the first lysosomal storage disorders to be treated with enzyme replacement therapy, in which a manufactured version of the missing enzyme is infused intravenously.

Genes Linked to Dementia and Serotonin Transport

Chromosome 17 carries the MAPT gene, which encodes the tau protein. Tau stabilizes microtubules inside neurons, the structural scaffolding that supports the long axons nerve cells use to communicate. When tau becomes abnormal and aggregates into tangles, neurons degenerate. Inherited mutations in MAPT cause frontotemporal dementia and parkinsonism linked to chromosome 17, an autosomal dominant condition in which patients develop personality changes, language difficulties, and motor symptoms, typically in their 40s or 50s.¹⁹ Three distinct subtypes of the disease are recognized based on which forms of tau accumulate in the brain, and the clinical presentation can mimic Alzheimer’s disease, progressive supranuclear palsy, or other dementias, making diagnosis tricky without genetic testing.²⁰

Also on chromosome 17 is SLC6A4, the gene encoding the serotonin transporter. This transporter is the molecular target of SSRIs, the most widely prescribed class of antidepressants. Functional variations in SLC6A4 have been associated with differences in pain perception and in how people respond to certain pain medications, which has made the gene a subject of pharmacogenomic research aimed at tailoring drug choices to a patient’s genotype.²¹

A Skeleton and Sex Determination Gene

SOX9, located at 17q24, is a transcription factor that plays dual roles in skeletal development and male sex determination. During embryonic development, SOX9 drives the formation of cartilage that later becomes bone, and in the developing gonad it acts downstream of the Y-chromosome gene SRY to trigger testis formation. Mutations that knock out one copy of SOX9 cause campomelic dysplasia, a severe skeletal malformation syndrome characterized by bowing of the long bones, and in many cases, XY sex reversal, in which a genetically male individual develops female external anatomy.²² The condition is inherited in a dominant fashion: losing just one functional copy of SOX9 is enough to cause both the bone and gonadal features, an example of haploinsufficiency.²³ Interestingly, the same frameshift mutation has been found in two unrelated XY patients, one of whom developed a male phenotype and the other a female phenotype, illustrating that the relationship between genotype and sex development is not perfectly predictable even within a single gene.

Why Chromosome 17 Keeps Rearranging Itself

A recurring theme in this article is that chromosome 17 disorders often involve deletions, duplications, or other structural rearrangements rather than simple point mutations. That is not a coincidence. The chromosome is loaded with low-copy repeats, large blocks of nearly identical DNA sequence scattered along its length. When chromosomes pair up during cell division, these repeats can misalign and recombine with the wrong partner, leading to pieces being swapped, lost, or gained.

Researchers have mapped the breakpoints of rearrangements across chromosome 17 and found that they cluster within known low-copy repeats, particularly structures designated LCR17pA, LCR17pB, and LCR17pC on the short arm.²⁴ These same repeat families are responsible for the NF1 microdeletions, the Smith-Magenis and Potocki-Lupski rearrangements, and the inversions at the MAPT locus. On the long arm, repeats near the centromere also mediate the formation of isochromosome 17q, a rearrangement commonly found in blood cancers and certain solid tumors in which the short arm is lost and replaced by a mirror-image copy of the long arm.²⁵ In cancers, the loss of 17p through isochromosome formation removes one copy of TP53, often the remaining wild-type copy, accelerating tumor progression.

A specific family of repeat elements called LRRC37-containing duplicons deserves mention because they mediate rearrangements at multiple locations on chromosome 17, including the NF1 region and the MAPT locus. These sequences are highly dynamic in the primate lineage and have independently triggered large inversions in humans, chimpanzees, and other primates.⁸ Their recombinogenic nature helps explain why chromosome 17 is such a frequent site of structural variation in both healthy populations and disease.

Emerging Therapeutic Strategies for Chromosome 17 Disorders

Many of the conditions tied to chromosome 17 have historically lacked disease-modifying treatments, but that picture is changing. Pompe disease already benefits from enzyme replacement therapy, and gene-therapy approaches are in development to provide a more durable correction. For HER2-positive breast cancers, targeted antibodies and antibody-drug conjugates have transformed outcomes over the past two decades. BRCA1-mutated cancers have become treatable with PARP inhibitors, drugs that exploit the DNA-repair deficit caused by BRCA1 loss to selectively kill tumor cells.

For neurological disorders, antisense oligonucleotides represent a promising frontier. These small synthetic DNA molecules can target specific messenger RNAs to reduce production of a harmful protein or restore expression of a missing one. Their success in treating spinal muscular atrophy has generated strong interest in applying the same approach to tauopathies and other neurodegenerative conditions linked to chromosome 17.²⁶ For gene-dosage disorders like CMT1A, where the problem is too much of a normal protein rather than a defective one, antisense strategies that reduce PMP22 expression are being explored in preclinical models. The challenge is delivering these molecules to peripheral nerves efficiently enough to restore normal myelin function without overshooting and causing the opposite disease, HNPP.

On the cardiovascular side, the ACE gene on chromosome 17 encodes angiotensin-converting enzyme, a key regulator of blood pressure. A common insertion/deletion polymorphism in ACE has been associated with the severity of coronary artery disease; in one study of patients with acute heart attacks, the DD genotype was independently linked to more extensive coronary blockages after adjusting for other risk factors.²⁷ ACE inhibitors are already a cornerstone of heart-disease treatment, but the genetic data raise the question of whether carriers of higher-risk genotypes might benefit from earlier or more aggressive intervention. That is an area where pharmacogenomics is still catching up with the biology.