Trisome

Trisomy is an abnormality in which an organism has the wrong number of chromosomes. In humans, a normal baby will have 46 chromosomes in 23 pairs, with each parent contributing 23 chromosomes. When trisomy occurs, the individual is born with three instances of a particular chromosome instead of the usual two, resulting in 47 total chromosomes instead of 46. The results of this extra data can vary, but tend to manifest in the form of birth defects, some of which can be quite severe.

The most common cause of trisomy is a problem in the duplication of chromosomes to create egg and sperm cells. Somewhere along the way, a chromosome duplicates itself twice, creating a full pair. When the egg or sperm cell joins with its counterpart, the extra chromosome is taken along, creating a set of three where should be two. In some cases, a chromosome only duplicates partially, leading to partial trisomy.

Some of the more well-known forms of trisomy are trisomies 13, 18, and 21. Trisomy 13 is also known as Patau syndrome, after the doctor who identified it. Patau syndrome is characterized by physical and mental defects, with heart defects being very common. Trisomy 18 is known as Edward's syndrome, and it is accompanied by severe mental and physical problems; most patients do not survive beyond a year. Trisomy 21 is Down's syndrome, a condition which is often accompanied by severe mental disabilities.

There are other forms; trisomy 16, for example, usually triggers a miscarriage, while trisomy 9 leads to malformations in the skull and nervous system. The number in each name refers to the chromosome in question; in some cases, patients have mosaic trisomy, meaning that the defect only shows up in certain cells. Trisomy 16 is believed to be the most common form in humans, while trisomy 21 is the most common form in viable infants.

It is possible to test for trisomy, along with other potential birth defects, and women who are at risk for the condition may undergo prenatal testing to check for it. If a prenatal test such as an amniocentesis reveals a trisomy, a doctor will discuss options with the patient. In some cases, doctors may recommend that the pregnancy be terminated, because the baby is nonviable. Some parents may choose to carry on with the pregnancy anyway, for ethical or moral reasons. Some people with trisomy leave happy, full lives, while other infants survive for only a short time after birth. 

​[tri´so-me]

the presence of an additional (third) chromosome of one type in an otherwise diploid cell (2n +1). adj., adj triso´mic.

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Trisomy 8 syndrome is a syndrome associated with an extra chromosome 8, usually mosaic (trisomy 8/normal), characterized by mild to severe mental retardation, prominent forehead, deep-set eyes, thick lips, prominent ears, and camptodactyly (abnormally flexed fingers).

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Trisomy 13 syndrome/ Patau's Syndrome 

Holoprosencephaly due to an extra chromosome 13, in which central nervous system defects are associated with mental retardation, cleft lip and palate, polydactyly (extra fingers or toes), and dermal pattern anomalies, as well as abnormalities of the heart, viscera, and genitalia.

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Trisomy 18 Syndrome/ Edwards Syndrome is a condition due to the presence of an extra chromosome 18, characterized by neonatal hepatitis, mental retardation, scaphocephaly or other skull abnormality, small receding mandible, blepharoptosis (drooping eyelids), low-set ears, corneal opacities, deafness, webbed neck, short digits, ventricular septal defects, Meckel's diverticulum, and other deformities. 

Information for families affected by this disorder and professionals caring for affected individuals can be obtained from the Support Organization for Trisomy 18, 13, and Related Disorders (S.O.F.T.), 2982 S. Union St., Rochester, NY 14624.

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Trisomy 21 Syndrome/ Down Syndrome.  Parents can find out more here: National Down Syndrome Society

Trisomy 21 is the most common chromosomal anomaly in humans, affecting about 5,000 babies born each year and more than 350,000 people in the United States.

Trisomy 21 is a genetic condition caused by an extra chromosome.  Babies with Down syndrome however, end up with three chromosomes at position 21, instead of the usual pair.

 

  Parents can find assistance here:  Support for Disorders of  Chromosome 22

Trisomy 22 is a chromosome disorder in which an extra (third) copy of chromosome 22 is present in every cell of the body where there should normally only be two copies. This condition is commonly found in miscarriages, but only rarely in liveborn infants. Most affected individuals die shortly before or shortly after birth due to severe complications. Common features include an underdeveloped midface (midface hypoplasia) with flat/broad nasal bridge, malformed ears with pits or tags, cleft palate, hypertelorism (wide-spaced eyes), microcephaly and other cranial abnormalities, congenital heart disease, genital abnormalities, and intrauterine growth restriction (IUGR).  

 

(Credits to: Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition.)

 

 

TRANSCRIPT:

s8e14 Trisomy

Lita T  00:08

Hello, and welcome to another episode of podcast dx, their show that brings you interviews with people just like you whose lives were forever changed by a medical diagnosis. I'm Lita.

Ron  00:19

I'm Ron,

Jean  00:20

and I'm Jean Marie.

Lita T  00:21

Collectively we're the hosts of podcast dx. March is trisomy Awareness Month, they're spelled t r i s o MY. With that in mind, we're going to talk about a few of the more common forms of trisomy today.

Ron  00:39

Right? Let's go over a bit of background here, humans have 23 pairs of chromosomes. And of these 22 are autosomes. The 23rd pair of chromosomes determines what genetic or physical sex characteristics an individual is born with, ie whether they're born male or female.

Jean  00:59

Okay, so let's picture 23 pairs of shoes and shoe boxes, numbered one to 23 lined up against a wall. Okay, if you open any one of those shoe boxes, you'll see two individual shoes that looks nearly identical mirror images of one another. If you counted up all of the shoes in the 23 shoe boxes, you would have 46 individual shoes in total. So 23 pair 46 total.

Lita T  01:27

Okay.

Jean  01:29

And now picture, there's a glitch in the mechanism at the shoe factory. They're going down. There is a hesitation in the assembly line and a mistake is made putting an extra shoe into one of the boxes that ends up in our shoe lineup. Now if you open that box, there's three shoes in there.

Lita T  01:47

Lucky, you

Jean  01:48

no not really

Lita T  01:49

because and you still have to use that extra shoe all the time.

Jean  01:53

Yep.

Lita T  01:53

So how do you do it?

Jean  01:55

not easily.

Lita T  01:55

 So it may sound as if we're making light of these conditions. But we're not we understand that genetic disorders are very serious and can be scary for new parents. Please keep in mind that these conditions are often a result of a random occurrence and not the parents fault. Please consult a qualified genetic counselor and your health care provider. If you or your partner have experienced a pregnancy loss because of trisomy, please take heed that it may not occur again. It's not like at all the time

Jean  02:29

right but a bit about approximately or it's thought that about half of pregnancy losses due to trisomy

Lita T  02:36

seek out physical and mental support. You're not alone.

Ron  02:41

Right, those are great points. Lita. Now getting back to trisomy the term trisomy was first used in the 1930s to describe a cell with an extra chromosome, kind of like what gene was talking about with the shoes. The route tri meaning three refers to a third chromosome, where there would typically only be a pair of chromosomes. trisomy is rare and may occur in some cells, mosaic trisomy or in all of the cells a full or complete trisomy, several forms of complete trisomy will not result in a live birth. There is also something called a partial trisomy, which occurs when there are two full chromosomes and a partial chromosome. But back to the shoe analogy two shoes. And let's say a shoe heel.

Lita T  03:35

That would be a partial

Ron  03:36

Yeah, right.

Jean  03:38

And yeah, what are you going to do with an extra heal? This specific diagnosis and his overall effect on an individual's physical, intellectual and developmental health will depend and which chromosome is affected and several other key factors, especially you know, is it mosaic or complete or partial? Typically individuals with trisomy have a distinctive forehead, eye and nose characteristic for that particular form of trisomy and health issues can vary widely and from nearly undetectable and have barely any symptoms to fatal.

Ron  04:15

right, right, right. Right. Now we're going to talk briefly about five of the more common autosomal forms of trisomy found in humans. trisomy 8, 9, 13, 18 and 21.

Lita T  04:31

Okay, trisomy eight, mosaic mosaic says

Jean  04:35

mosaicism

Lita T  04:36

mosaicism mosaicism syndrome, that's hard to say abbreviated as T 8 MS occurs when there are three number eight chromosomes. So the eight, so the number is referred to as the number of chromosomes.

Jean  04:55

Nope.

Ron  04:56

Well, it's like the pair of shoes she was talking about

Lita T  04:57

Oh number eight chromosome.

Jean  04:59

So looking Back at my rather convoluted analogy...

Lita T  05:02

Yeah

Jean  05:02

... in shoe box number eight

Lita T  05:04

Okay, okay

Jean  05:04

 along the wall, you have three shoes,

Lita T  05:06

okay instead of two,

Jean  05:08

right

Lita T  05:09

 Um, and individuals with trisomy eight mosaicism syndrome have a third copy of chromosome eight in some, but not all of their cells.

Ron  05:22

Yeah,

Lita T  05:22

okay.

Ron  05:23

 So trisomy eight mosaicism syndrome is also known as Warkany Syndrome 2 individuals with this genetic disorder may have intellectual disabilities and or issues with their joints, especially in the knees. They may also have problems with their kidneys, their heart, their spine, and or their skeletal system. And it occurs far more often, four to one ratio in those born with male reproductive organs than those born with female reproductive organs. It is typically the result of a random change in the chromosomes. But it is not something that is typically inherited. Individuals with trisomy eight mosaicism syndrome may be more susceptible to infections and at a higher risk for some cancers.

Jean  06:18

On to trisomy nine, complete and mosaic. trisomy nine are rare chromosomal conditions which are often fatal. The life span for individuals with partial trisomy nine may not be affected. So if you have

Lita T  06:34

complete

Jean  06:34

 if you have an extra chromosome in all of your alongside all of your nine, or if you have it in most of your cells, then it's fatal, or most likely fatal. And if you have it just a little piece of chromosome extra piece of chromosome nine, you might be fine.

Lita T  06:53

 Okay

Jean  06:54

 Your lifespan might be fine,

Lita T  06:55

okay. Some signs and symptoms of partial trisomy nine may include heart spinal cord and brain defects, which may be detected with prenatal ultrasound. Partial trisomy nine may also result in issues with the individual's head and nose shape, the joints, the eye, and also kidney problems. These individuals may have cognitive and developmental delays.

Ron  07:25

And then I think it's pronounced Patau?

Lita T  07:30

 Patau ?

Ron  07:31

Patau syndrome, or better known, I guess, is trisomy 13. This is often fatal in infancy. And again, this condition is a result of a random chromosomal change. It may affect the heart, the brain, the spine, eyes, fingers, toes, and basically the overall muscle tone of the individual.

Jean  07:55

And then there's um, trisomy 18, which is also known as Edwards syndrome, which is often fatal. Those individuals who do not live past their first year of life may have severe intellectual challenges, defects in the internal organs and heart. Their fists may be constantly clenched and their fingers may overlap. And that's a distinctive feature of trisomy 18.

Lita T  08:20

Okay? And trisomy 21, also known as Down syndrome, is one of the more common and well known forms of autosomal autosomal,  autosomal trisomy, individuals with trisomy 21 may have mild to severe intellectual disabilities. Typically, children with Down syndrome reach developmental milestones a bit late, the lifespan for individuals with Down syndrome has been increasing. Jean said that Well, back in the, well, I, we had a neighbor who had Down syndrome when I was young.

Jean  08:32

autosomal,  Mhhmm

Lita T  09:00

 And we were talking about when I was like, eight, and I think he lived to maybe 40 years old. What's the lifespan? Now?

Ron  09:10

ummm 60 isn't it?

Jean  09:11

Yeah, it isn't, it is in the 60s, it went from like 25 to 60 in a rather short period of time, and the more that we realize that individuals with Down syndrome, you know, are capable of living...

Ron  09:23

Right

Jean  09:23

... a full and rich life, the longer the lifespan will, you know, be

Ron  09:27

a lot of it has to do with integrating into s...