Chromosome 21 News and Research

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Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 21, one copy inherited from each parent, form one of the pairs. Chromosome 21 is the smallest human chromosome, spanning about 47 million base pairs (the building blocks of DNA) and representing approximately 1.5 percent of the total DNA in cells.

In 2000, researchers working on the Human Genome Project announced that they had determined the sequence of base pairs that make up this chromosome. Chromosome 21 was the second human chromosome to be fully sequenced.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 21 likely contains between 300 and 400 genes.

Genes on chromosome 21 are among the estimated 20,000 to 25,000 total genes in the human genome.

Study uncovers biological differences behind co-occurring conditions of Down syndrome

In a groundbreaking new study published in Nature Communications, researchers from the University of Colorado Anschutz Linda Crnic Institute for Down Syndrome (Crnic Institute) discovered unique biological processes altered among individuals with Down syndrome who have different sets of co-occurring conditions.

23 Jul 2026

Hidden junk DNA could play decisive role in cancer

Many repetitive regions of the genome have been considered "junk DNA" because the technologies available did not allow them to be studied at sufficient resolution.

5 Jun 2026

Neurodegeneration in Down syndrome may begin shortly after birth

Signs of neurodegeneration in individuals with Down syndrome may start as early as birth, a critical stage of brain development, a new study shows.

8 May 2026

Study maps the evolution of myeloid leukemia in children with Down syndrome

It may be possible to identify which pre-cancerous cells will develop into a rare type of blood cancer, due to new research showing that a single genetic change drives myeloid leukemia in children with Down syndrome.

23 Apr 2026

Excessive RNA editing enzyme alters brain circuit formation in Down syndrome

A collaborative research study co-led by scientists at the Icahn School of Medicine at Mount Sinai and the Liber Institute for Brain Development has for the first time identified a biological process that may help explain how the brain develops differently in people with Down syndrome.

31 Mar 2026

New discovery could reshape how scientists think about Alzheimer’s treatment

Rutgers neuroscientist Peng Jiang was visiting his hometown of Qianshan, a city in China's Anhui province, when a neighbor came to his parents' house with a story that would stay with him.

24 Nov 2025

UC Davis researchers lead $5.5 million study on language development in children with Down syndrome

UC Davis researchers are leading a $5.5 million study to better understand how children with Down syndrome develop expressive communication - the skills used to share what we want, think or feel.

21 Nov 2025

Nuclear binding protein identified as key contributor to trisomy 21-related CHDs

Three copies of chromosome 21 causes Down syndrome (DS), and roughly half of children born each year in the United States with DS-approximately 2,600-also have congenital heart defects (CHDs).

22 Oct 2025

HMGN1 gene linked to heart problems in people with Down syndrome

Nearly half of all babies born with Down syndrome face congenital heart defects, often involving serious malformations that require surgery in the first months of life.

22 Oct 2025

Study links high neuroinflammation in young people with Down Syndrome to Alzheimer's risk

Down syndrome is associated with accelerated aging. It is estimated that up to 90% of individuals with the condition develop Alzheimer's disease before the age of 70. A study by researchers at the University of São Paulo (USP) in Brazil identified high levels of neuroinflammation in young individuals with Down syndrome, an additional factor explaining the high prevalence of Alzheimer's disease in older people with the condition. The discovery paves the way for strategies to prevent and monitor the disease.

3 Oct 2025

Researchers uncover how chromosome crossovers protect fertility

When a woman becomes pregnant, the outcome of that pregnancy depends on many things - including a crucial event that happened while she was still growing inside her own mother's womb.

24 Sep 2025

Lifespan study reveals age-specific biological changes in Down Syndrome

In a groundbreaking new study published in Nature Communications, researchers from the Linda Crnic Institute for Down Syndrome (Crnic Institute) at the University of Colorado Anschutz discovered important differences in the physiological changes observed in over 300 individuals with Down syndrome across the lifespan.

24 Sep 2025

Adults with both Down Syndrome and congenital heart defects show remarkable resilience

Adults with both Down Syndrome and congenital heart defects, also known as congenital heart disease (CHD), are showing remarkable resilience despite facing significant medical challenges, according to a new MUSC study in Pediatric Cardiology.

19 Sep 2025

Study finds high levels of iron in the brains of people diagnosed with Down syndrome and Alzheimer's

Scientists at the USC Leonard Davis School of Gerontology have discovered a key connection between high levels of iron in the brain and increased cell damage in people who have both Down syndrome and Alzheimer's disease.

19 Jun 2025

Brain stimulation at 40Hz boosts memory and neurogenesis in Down syndrome mice

Study provides new evidence that sensory stimulation of gamma-frequency brain rhythm may promote broad-based restorative neurological health response.

25 Apr 2025

Study reveals key mechanisms behind cancer cells adapting to extra chromosomes

Cancer cells have special adaptation mechanisms that allow them to proliferate despite changes in their genetic makeup.

13 Feb 2025

New study links genetic mosaicism to lower Alzheimer’s risk in adults with Down syndrome

Study finds mosaicism in Down syndrome reduces Alzheimer's risk, providing new insights into genetic influences on cognitive decline and dementia progression.

8 Nov 2024

Why children with Down’s syndrome are predisposed to developing leukaemia

The study uncovers mechanisms linking Down syndrome to leukemia, emphasizing the role of oxidative stress and genetic alterations in fetal blood development.

26 Sep 2024

Study uncovers genetic changes linked to leukemia risk in people with Down's syndrome

People with Down's syndrome face a higher risk of developing Leukemia. Now researchers from the University of Copenhagen and Stanford University explain why, by identifying specific changes in blood cells of people with Down's syndrome.

25 Sep 2024

Coordinated health teams may help improve outcomes for children with Trisomy 21 and heart conditions

A coordinated, multidisciplinary health care team to address the specific physical, psychological and developmental needs of children with Trisomy 21, or Down syndrome, and congenital heart disease may help children with these conditions lead longer and more productive lives, according to a new scientific statement from the American Heart Association.

13 Sep 2024