Chromosome 16 carries roughly 880 protein-coding genes spread across nearly 79 million base pairs of DNA, making it a mid-sized but gene-dense chromosome with an outsized influence on human health. Its genes are involved in oxygen transport, kidney function, brain development, immune regulation, cancer susceptibility, and more. Because so many of these genes are well-studied and linked to recognizable conditions, chromosome 16 offers a useful window into how a single chromosome can touch nearly every organ system in the body.
Size, Structure, and Gene Content
The finished sequence of chromosome 16 spans about 78.9 million base pairs of euchromatin (the gene-rich portion), encoding 880 confirmed protein-coding genes along with 19 transfer RNA genes and 341 pseudogenes.1PubMed. The sequence and analysis of duplication-rich human chromosome 16 That gene count makes it one of the more densely packed chromosomes relative to its length. One of chromosome 16’s defining structural features is its abundance of segmental duplications, large blocks of DNA that have been copied and pasted to other locations on the same chromosome or elsewhere in the genome. These duplications are not just evolutionary fossils. They create hotspots of genomic instability where DNA can be rearranged, deleted, or duplicated during cell division, and many of the clinical conditions tied to chromosome 16 trace back to these unstable regions.
A repeat element called LCR16a has been identified as a major driver of these interspersed duplications, and it appears to be an ancient feature of primate genomes. The gene family it carries, called NPIP, underwent dramatic structural changes and bursts of positive selection specifically in the African ape lineage, suggesting it has been under strong adaptive pressure for millions of years.2PubMed Central. An evolutionary driver of interspersed segmental duplications in primates This evolutionary instability is not just an academic curiosity. At the 16p12.2 locus alone, researchers examining hundreds of diverse human genomes found that haplotypes vary enormously in size and architecture, with certain duplicated segments mediating the deletions that cause neurodevelopmental disorders.3PubMed Central. Evolutionary instability drives structural diversity and disease susceptibility at the 16p12.2 locus
Alpha-Globin Genes and Blood Oxygen Transport
One of the most clinically significant gene clusters on chromosome 16 sits near the tip of its short arm: the alpha-globin genes. Humans carry four copies of these genes (two on each copy of chromosome 16), and they encode a critical component of hemoglobin, the protein in red blood cells that carries oxygen. When one or more of these gene copies is deleted or mutated, the result is alpha-thalassemia, one of the most common inherited blood disorders worldwide. The severity scales directly with how many copies are affected. Losing one copy usually produces no symptoms at all. Losing two causes mild anemia. Losing three leads to a condition called hemoglobin H disease, with moderate to severe anemia. Losing all four is almost always fatal before or shortly after birth.4PubMed. Molecular basis of α-thalassemia
Alpha-thalassemia is especially common in populations from Southeast Asia, sub-Saharan Africa, and the Mediterranean, where carrying one or two deleted copies may have historically offered some protection against malaria. Because the condition ranges from clinically invisible to lethal depending on the number of gene copies lost, many carriers have no idea they carry the trait until genetic testing or a blood count reveals unusually small red blood cells.
Polycystic Kidney Disease
Chromosome 16 is home to PKD1, the gene responsible for roughly 85% of cases of autosomal dominant polycystic kidney disease (ADPKD), one of the most common life-threatening genetic disorders.5PubMed. Polycystic kidney disease. 1: Identification and analysis of the primary defect ADPKD causes fluid-filled cysts to grow progressively in both kidneys, often leading to kidney failure by middle age. The disease affects an estimated 1 in 400 to 1 in 1,000 people, making it one of the most frequent reasons for kidney transplant.
The PKD1 gene, located at 16p13.3, encodes a large protein called polycystin-1 that sits in cell membranes and helps cells communicate with the surrounding tissue.6PubMed. The polycystic kidney disease 1 gene encodes a 14 kb transcript and lies within a duplicated region on chromosome 16 When polycystin-1 does not work properly, cells lose the signals that normally keep tubular structures in the kidney organized, and cysts begin to form. Identifying PKD1 was complicated by the fact that most of the gene lies within one of chromosome 16’s duplicated regions, meaning there are several look-alike segments nearby that initially confused researchers trying to pinpoint the real gene.5PubMed. Polycystic kidney disease. 1: Identification and analysis of the primary defect This structural quirk of chromosome 16 made the gene one of the harder disease genes to clone in the 1990s.
The 16p11.2 Region and Brain Development
A stretch of chromosome 16 called 16p11.2 has become one of the most studied regions in neurogenetics. Deletions or duplications of this roughly 600-kilobase segment are among the most common copy-number variants linked to neurodevelopmental conditions, including autism spectrum disorder and intellectual disability. Because the region sits within one of chromosome 16’s duplication-rich zones, it is prone to rearrangement during the formation of egg and sperm cells.
Deletions and duplications of 16p11.2 produce mirror-image effects on body and brain size. People carrying a deletion tend to have larger head circumference and higher body mass index, while those carrying a duplication tend toward smaller head circumference and lower BMI. A large study found that about 22% of duplication carriers met criteria for microcephaly, and their risk of obesity was roughly three times lower than in control groups.7JAMA Psychiatry. Defining the Effect of the 16p11.2 Duplication on Cognition, Behavior, and Medical Comorbidities About 20% of duplication carriers in that study met diagnostic criteria for autism, a rate similar to that seen in deletion carriers, but duplication carriers with autism scored substantially lower on cognitive measures, by an average of 26 points.
Brain imaging research has confirmed that these copy-number changes physically reshape the brain. Total brain volume, gray matter, white matter, and cortical surface area all decrease as gene dosage at 16p11.2 increases (that is, from deletion to normal to duplication). Interestingly, cortical thickness was reduced in both deletion and duplication carriers compared to controls, making it the one brain measure that does not follow the simple linear dosage pattern.8Molecular Psychiatry. The 16p11.2 locus modulates brain structures common to autism, schizophrenia and obesity These findings illustrate how sensitive brain development is to having the right number of gene copies in this particular region.
Immune System Genes
Chromosome 16 hosts several genes that shape how the immune system recognizes and responds to threats. Two of the best-characterized examples involve Crohn’s disease and familial Mediterranean fever (FMF), conditions that seem very different on the surface but both involve an overactive inflammatory response.
The NOD2 gene on chromosome 16 was one of the first genes convincingly linked to Crohn’s disease, a form of inflammatory bowel disease. NOD2 encodes a pattern-recognition protein that helps the innate immune system detect bacterial components. Certain variants in the gene’s sensing region appear to alter how the immune system responds to gut bacteria, tipping the balance toward chronic inflammation.9PubMed. The Nod2 gene in Crohn’s disease: implications for future research into the genetics and immunology of Crohn’s disease Not everyone with NOD2 variants develops Crohn’s, but the discovery helped establish that genetic variation in innate immunity plays a central role in inflammatory bowel disease.
FMF, meanwhile, is the most common monogenic autoinflammatory disease in the world, particularly prevalent among people of Mediterranean descent, including Turkish, Armenian, Arab, and Jewish populations. It is caused by mutations in the MEFV gene on chromosome 16, which encodes the protein Pyrin. When Pyrin carries FMF mutations, it bypasses a normal safety check that requires intact microtubules (structural components of the cell skeleton) for its activation. In healthy cells, disassembling microtubules shuts down Pyrin-driven inflammation. In FMF patients’ cells, Pyrin fires regardless, triggering intense episodes of fever, abdominal pain, and joint inflammation.10PubMed Central. Familial Mediterranean fever mutations lift the obligatory requirement for microtubules in Pyrin inflammasome activation Colchicine, the standard treatment for FMF, works precisely by stabilizing microtubules, which helps explain why it is so effective for this specific condition.
Cancer-Related Genes
Several genes on chromosome 16 are directly involved in cancer development. Two stand out for their clinical importance.
The CDH1 gene encodes E-cadherin, a protein that acts like molecular glue between cells in epithelial tissues (the sheets of cells lining the stomach, breast, and other organs). E-cadherin functions as a tumor suppressor: as long as it works, cells stick together and grow in an organized way. When CDH1 is mutated, cells lose their adhesion and can invade surrounding tissues. Inherited mutations in CDH1 cause hereditary diffuse gastric cancer, a particularly aggressive form of stomach cancer that runs in families. Beyond inherited mutations, the gene can also be silenced by chemical modifications to DNA in non-inherited cancers.11PubMed Central. E-cadherin and gastric cancer: cause, consequence, and applications People identified as carrying CDH1 mutations are often advised to consider preventive removal of the stomach, which gives a sense of how serious the cancer risk is.
Chromosome 16 also plays a role in a subtype of acute myeloid leukemia (AML). A chromosomal rearrangement called inversion 16, which flips a segment of the chromosome’s short arm so it fuses with a segment on the long arm, creates an abnormal fusion between the CBFB and MYH11 genes. This fusion protein disrupts normal blood cell development. Paradoxically, AML carrying this inversion is classified as favorable-prognosis because patients tend to respond well to chemotherapy compared to other AML subtypes.12PubMed. AML with inv(16)/t(16;16) and high-risk cytogenetic abnormalities: atypical features and unfavorable outcome
MC1R and Red Hair
The MC1R gene, located on chromosome 16, is the primary genetic determinant of red hair. MC1R encodes a receptor on the surface of pigment-producing cells that controls the balance between two types of melanin: the darker eumelanin and the reddish-yellow pheomelanin. When MC1R loses function, pigment-producing cells shift toward making pheomelanin, producing red hair and fair skin. Three specific loss-of-function variants in MC1R are strongly associated with red hair, while three additional variants have weaker but measurable effects, with their influence differing by about two orders of magnitude.13PubMed Central. A study in scarlet: MC1R as the main predictor of red hair and exemplar of the flip-flop effect
The MC1R connection extends beyond cosmetic appearance. Loss-of-function variants increase susceptibility to UV damage and are associated with higher risk of melanoma and other skin cancers, even in people who do not have overtly red hair. Because MC1R variants are relatively common in Northern European populations, they represent one of the clearest examples of how a single gene on chromosome 16 can influence both a visible trait and disease risk simultaneously.
Trisomy 16
Having an extra copy of chromosome 16, known as trisomy 16, is the single most common chromosomal abnormality found in first-trimester miscarriages. A complete extra copy is incompatible with life, and pregnancies with full trisomy 16 almost always end in early loss.14PubMed Central. Outcomes of pregnancies with trisomy 16 mosaicism detected by NIPT: a series of case reports However, mosaic trisomy 16, where only some of the body’s cells carry the extra chromosome while others are normal, can result in a live birth. Even in mosaic cases, pregnancies tend to be complicated. A review of outcomes found that about 71% of mosaic trisomy 16 pregnancies delivered preterm, roughly 74% of babies had birth weights below the 10th percentile, and about 60% had congenital anomalies.15Genetics in Medicine. Mosaic trisomy 16: what are the obstetric and long-term childhood outcomes?
The picture for children who survive is more encouraging than the pregnancy complications might suggest. In the same study, about 82% of school-aged children with mosaic trisomy 16 were in mainstream classes, and their quality-of-life scores were high across physical and psychosocial measures.15Genetics in Medicine. Mosaic trisomy 16: what are the obstetric and long-term childhood outcomes? This gap between a very rough pregnancy and a relatively normal childhood outcome is worth knowing about for families facing this diagnosis through prenatal screening.
Aortic Disease and Smooth Muscle
The MYH11 gene on chromosome 16 encodes beta-myosin heavy chain, a protein essential for the contraction of smooth muscle cells in blood vessel walls. Mutations in MYH11 are an established cause of familial thoracic aortic aneurysms and dissections (TAAD), a dangerous condition where the wall of the aorta weakens and can tear. Beyond point mutations, duplications of the 16p13.1 region that include MYH11 have also been identified as a risk factor. Researchers found that people with TAAD who carried 16p13.1 duplications had increased MYH11 gene expression in their aortic tissue compared to controls.16PLoS Genetics. Recurrent Chromosome 16p13.1 Duplications Are a Risk Factor for Aortic Dissections Too much of this protein, however, does not appear to translate into more functional contractile machinery in the vessel wall. The hypothesis is that overproduction creates an imbalance with partner proteins, leading to degradation and ultimately weakening the smooth muscle cells that are supposed to keep the aorta intact.17American Journal of Human Genetics. Rare Copy Number Variants Disrupt Genes Regulating Vascular Smooth Muscle Cell Adhesion and Contractility in Sporadic Thoracic Aortic Aneurysms and Dissections
Electrolyte Balance and Gitelman Syndrome
The SLC12A3 gene on chromosome 16 encodes a sodium-chloride co-transporter in the kidney that reclaims salt from urine before it leaves the body. When both copies of this gene carry loss-of-function mutations, the result is Gitelman syndrome, a condition marked by low blood levels of potassium, magnesium, and chloride.18PubMed Central. The genetic spectrum of Gitelman(-like) syndromes Symptoms range from muscle cramps and fatigue to heart rhythm disturbances in more severe cases. Gitelman syndrome is recessive, so you need mutations on both chromosome copies to develop the full condition. Carriers with a single mutated copy were long thought to be unaffected, but recent large-scale genetic studies have found that even heterozygous carriers tend to have measurably lower serum potassium levels, suggesting the gene has a dose-dependent effect even when only half its function is lost.19PubMed Central. Heterozygosity for a Pathogenic Variant in SLC12A3 That Causes Autosomal Recessive Gitelman Syndrome Is Associated with Lower Serum Potassium
Rarer Conditions Linked to Chromosome 16
Beyond the conditions discussed above, chromosome 16 harbors genes involved in several rarer but instructive disorders. The GAN gene encodes gigaxonin, a protein that helps clear intermediate filaments (structural proteins inside nerve cells). When GAN is mutated, these filaments pile up and swell the nerve fibers into characteristic “giant axons,” causing giant axonal neuropathy, a progressive and severe childhood-onset neurological disease that impairs both motor and sensory nerves.20PubMed. A review of gigaxonin mutations in giant axonal neuropathy (GAN) and cancer
The CLN3 gene, also on chromosome 16, is linked to CLN3 disease (the juvenile form of Batten disease), a neurodegenerative storage disorder that typically begins in early childhood with vision loss and progresses to seizures, cognitive decline, and motor impairment. Recent research in animal models has found that CLN3 mutations disrupt brain development very early, with measurable biochemical changes appearing in the hippocampus by postnatal day 11, well before clinical symptoms emerge.21Scientific Reports. CLN3 disease disrupts very early postnatal hippocampal maturation These findings suggest the disease is not purely degenerative but also involves abnormal development from the start, a distinction that could influence future treatment strategies.
Chromosome 16 Across Species
Comparing chromosome 16 across species reinforces just how central many of its genes are to basic mammalian biology. Mouse chromosome 16, for example, shares large blocks of conserved gene content and order with human chromosomes 3, 8, 12, 16, 21, and 22.22PubMed. A comparison of whole-genome shotgun-derived mouse chromosome 16 and the human genome That conservation means many genes on human chromosome 16 have been performing similar functions for tens of millions of years since mice and humans last shared a common ancestor. It also makes mouse models valuable for studying chromosome 16 diseases like polycystic kidney disease and Batten disease, since the relevant genes are present and organized in comparable ways. What is unique to humans and our closest primate relatives, however, is the extraordinary level of segmental duplication on chromosome 16, which has made it one of the most structurally variable chromosomes in the human genome and a continuing source of both evolutionary innovation and genetic disease.