In every cell in the human body there’s a large rod-like structure called a chromosome. These chromosomes have 23 pairs of DNA (genetic information) that are normally inherited from one parent.
A change in a chromosome is what causes Down syndrome. Trisomy 21 is the most common form, accounting for 95% of all cases.
Genetics
Genetics is the study of genes, heredity and variation in living organisms. All genetic information is inherited from parents through the chromosomes in their cells. There are 23 pairs of chromosomes in every cell, each containing one X and one Y chromosome from each parent.
In human beings, each pair of chromosomes contains the DNA code for all the genes in our body. The chromosomes are arranged in a rod-like structure called the nucleus. Each pair of chromosomes has 23 copies of the DNA in it, which makes up a full set of 46 chromosomes (23 pairs
When an egg or sperm cell splits to create two daughter cells, it divides all 23 pairs of chromosomes. These chromosomes contain the genes that make us unique from other animals.
A person with Down syndrome has a full or partial extra copy of chromosome 21 (trisomy 21). This happens when one copy of the chromosome is attached to another chromosome during a process called non-disjunction in cell division.
The extra copy of chromosome 21 can disrupt the normal development of an individual, leading to the characteristic features found in those with Down syndrome. There are two different ways that this happens.
Despite the similarities between humans and monkeys, there are no reports of monkeys with down syndrome. Some animals, such as Kenny the tiger or Otto the kitten, have traits that look like down syndrome but may not be related to the condition at all.
Pregnancy
Pregnancy is the time when a woman’s body undergoes many changes. This period of time can be a stressful and exciting time for both the mother and her unborn child.
When the egg cells are fertilized, a new cell (zygote) develops in the uterus and fuses with the sperm. This zygote then becomes a fetus, and continues to grow inside the uterus surrounded by amniotic fluid until it is born.
While humans have a unique genetic make-up, there are some animals that have chromosomal abnormalities that can be similar to those found in Down syndrome. For example, mice can have a trisomy in chromosome 16, a condition that is very similar to Down syndrome.
However, this chromosomal abnormality is not seen very often in animals. It is believed that if this chromosomal abnormality did occur, it would be impossible to identify the condition until after the animal was born.
Fortunately, Japanese scientists have confirmed that a 24-year-old female chimp named Kanako has Down syndrome. She was born in captivity at the Kumamoto Sanctuary and had some unusual traits that set her apart from other chimps.
Her blindness makes social interaction difficult, but her caretakers are doing all they can to help Kanako live a normal life. She lives separated from other chimps to avoid aggressive interactions, but is provided with opportunities to interact with another chimp once a month.
Birth
The birth of a baby with down syndrome in monkeys is rare but is possible. The condition, also known as trisomy 21, is caused by an extra chromosome that duplicates the 21st chromosome.
The condition affects a small percentage of humans but it can occur in other mammals, such as chimpanzees and apes. It is very rare, and only two cases have been reported to science worldwide (McClure et al. 1969).
One of these apes is Kanako, who was born in 1992 at the Kumamoto Sanctuary in Japan. She has stunted growth, underdeveloped teeth, congenital heart disease and partial blindness resulting from a progressive thinning of her corneas.
Researchers confirmed that she has a third copy of the 22nd chromosome, and that she has Down syndrome. The chimp has had a long and troubled life, but she is now living at a research center in Kyoto University.
Grete Falt-Hansen, who heads the national down syndrome association in Denmark, says she gets calls from women every few weeks whose first-trimester screening results said their child had no chance of being diagnosed with Down syndrome. Falt-Hansen counsels them about what life is like for a child with Down syndrome.
Having a child with Down syndrome is a very difficult situation, but the best way to cope with it is to love your child. As a parent of a child with down syndrome herself, she knows what it means to love someone who has this condition.
Development
A 24-year-old chimpanzee named Kanako recently was diagnosed with down syndrome. This marks the first documented case of this condition in a chimp. She was born at the Kumamoto Sanctuary in Japan and developed several abnormal characteristics that set her apart from other chimps.
For example, she had crossed eyes and cataracts when she was a year old. She also had some heart irregularities and underdeveloped teeth.
Japanese researchers analyzed her chromosomes and discovered that she has trisomy 22, which is a chromosomal disorder that causes Down syndrome in humans. This chromosomal disorder is similar to Down syndrome in apes such as chimpanzees and gorillas, where a third copy of chromosome 21 causes this condition (Richard and Dutrillaux 1998).
There are two different processes that lead to the development of down syndrome. One occurs during cell division, which leads to the daughter acquiring an extra copy of chromosome 21, called trisomy 21. The other occurs when a 21st chromosome is transferred to another chromosome during cell division, called translocation.
In addition to having a rare chromosomal disorder, the chimp also suffered from hypodontia, infantile cataracts, limited growth and vision issues. These symptoms are typical of people with Down syndrome.
She was treated at the Kyoto University hospital, where she was given a variety of medication to control her symptoms. She died peacefully at the age of 27 in February 2020.
Diseases
The symptoms of down syndrome in monkeys are often misunderstood, as many animals have chromosomes that do not contain the extra copy of chromosome 21. For example, tigers have only 19 pairs of chromosomes, and cats have no chromosome 21, making them unlikely to have the condition.
However, Down syndrome does occur in apes such as chimpanzees and gorillas, because their cells have an extra copy of chromosome 22. This chromosomal abnormality is also called trisomy 22, which occurs in up to 1 in 600 births.
Normally, humans have 23 pairs of chromosomes (for a total of 46), and apes have 24 pairs of chromosomes (for 48). When apes have trisomy 22, the genetic material on their chromosomes is distorted, which results in a variety of symptoms.
For example, monkeys with down syndrome often have clubbed digits and curved pinkies, as well as a wide 1-2 toe gap. They also have shortened statures and an increased risk of congenital heart disease.
Another example of a chromosomal abnormality in apes is Hirschsprung’s disease, a form of arthritis. This is characterized by joint stiffness and swelling that can lead to pain, loss of mobility and disability.
Kanako, a 24-year-old female chimp at Kumamoto Sanctuary in Japan, was found to have trisomy 22 after she was diagnosed with several health problems. Besides having crossed eyes, she was blind by age seven, and her vision issues included nystagmus, strabismus and keratoconus, which are eye conditions that can cause the thinning of the corneas.
Treatment
Cynomolgus monkeys (Macaca fascicularis) are commonly used for safety testing in drug development because they are physiologically and anatomically close to humans. They are also popular pets for people with disabilities.
When apes like chimpanzees, gorillas and orangutans have an extra copy of chromosome 22 (also known as trisomy 22) in their cells, they can develop Down syndrome. The first confirmed case of a chimp with this disorder was documented in 1969.
Kanako, a 24-year-old chimp, has recently been confirmed to have trisomy 22 by researchers from Kyoto University in Japan. She is the longest living chimp with this chromosomal disorder that scientists know of.
She has stunted growth, suffers from a congenital heart disease and has underdeveloped teeth. She also has crossed eyes and a disorder that causes her corneas to progressively thin, similar to vision problems in Down syndrome patients.
Her caretakers didn’t realize she had trisomy 22 until 2014, when they noticed she had a hole in her heart during a routine physical exam. This led to them analyzing her chromosomes.
Although the chromosomal abnormality has caused Kanako a variety of problems, she is otherwise healthy and socially engaged. Her caretakers hope the diagnosis will help them provide her with a better quality of life.
