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What is tetrasomy?

Tetrasomy 9p

How is tetrasomy 9p diagnosed?

Why are some people with tetrasomy 9p more severely affected than others?

How did this happen?

A tetrasomy is a form of aneuploidy with the presence of four copies, instead of the normal two, of a particular chromosome.

Palate Abnormalities of the roof of the mouth affected 23 babies out of 41.

Abnormalities can range from those invisible to the casual onlooker (a high palate, a divided uvula, the projection of soft tissue that hangs down from the back of the mouth) to an obvious defect with a divided upper lip and a large gap in the roof of the mouth.

A cleft lip palate causes difficulty in feeding and speech production. Surgical repair eases these and may eliminate them.

Teeth

In the great majority of children, the extra material from 9p appears as a separate, small

chromosome.

Children with rare chromosome disorders are at risk for dental problems.

far always revealed

When the blood of parents with an affected child is examined, it has so

normal chromosomes.

One possible solution in this situation is to take a sample of blood from the umbilical cord, as this blood is part of the fetal circulation. This procedure can be risky, however, and one couple at high risk of having a baby with tetrasomy 9p who lost a pregnancy after fetal blood sampling chose instead to have future pregnancies intensively monitored by amniocentesis and ultrasound with the sonographer looking for findings such as an enlarged head, growth delay and palate, lip and kidney anomalies.

A high standard of dental care is important to minimise damage by decay and erosion (by grinding)

failure of the chromosomes

The

most common reason for the extra chromosome is the

eggs or sperm, leading to

an

9 in one parent to separate in the process of preparing the

extra whole chromosome 9.

This extra chromosome is

leaving it

believed to then undergo an unusual type of division,

bottom halves (the long arms) are lost.

(short arms) while the two

with two top halves

Brachycephaly - the head is disproportionately wide

ear-to-ear

A rare chromosomal disorder where there is four copies of the short arm of chromosome 9 (9p) instead of the normal two resulting in various abnormalities.

compared to the measurement from front to back

frequent problem that occurs after birth is hydrocephalus,

The most

usually requiring a shunt to

drain the excess cerebrospinal fluid and

relieve pressure on the growing brain.

Other typical features

Unusually formed nails; a single crease across the palm; incurving fingers, especiallythe fifth finger; short hands and feet with small toe and finger joints

Widely spaced eyes; small skin folds across the inner corner of the eyes; eyes thatslant somewhat downwards; a small lower jaw, set back from the upper jaw;downwards slanting mouth

Low muscle tone, making the body feel floppy (hypotonia)

Unusual head size – small (microcephaly) or large (macrocephaly). Enlarged fluidfilledventricles within the brain (hydrocephaly)

Down’s

Separation failure, termed non-disjunction, is more common in older mothers (as in

higher than

syndrome) and the age of mothers having a child with tetrasomy 9p is slightly

average.

20 to

years (range

The average age of mothers of babies with the mosaic form is 33.7

that of fathers

42 years), compared with a population average of 26-9 years, while

was 34.9 years.

Growth delay before or after birth

Heart defects

Abnormalities of the kidneys or urinary system. In boys, minor anomalies of the genitals or undescended testicles are common.

At birth, wide gaps between the bony plates of the skull. The front soft spot(fontanelle) may be large

Short neck, sometimes with excess skin

Cleft lip, palate or a high-arched palate

Can it happen again?

Heart

Seen in non-mosaic form only

Babies with a mosaic form of tetrasomy 9p have a better outcome.

A structural heart anomaly has been found in around one third of children and adults with mosaic tetrasomy 9p.

Underdeveloped lungs, possibly due to diminished fetal movement, sometimes with unusual lobe pattern and bronchopulmonary dysplasia

As tetrasomy 9p is most likely to appear to be non-mosaic in blood, it is important that

all babies with the diagnosis made from a blood test have

Biliary atresia

Malrotation of part of the intestine

the body (such as skin or mucous membranes)

tissue from another part of

Diaphragmatic hernia

to show mosaicism.

examined as well, as this is more likely

The condition is treated through an operation called Kasai-portoenterostomy in which a loop of bowel is used to form a duct to drain bile from the liver.

Underdeveloped bladder

Inflammation of bile duct to the liver, causing blockage of the flow of bile and jaundice.

Diagnosis during pregnancy is more difficult as tetrasomy 9p cells may not be found in fetal cells in amniotic fluid. It is therefore quite possible for a pregnancy to be affected by tetrasomy 9p but for the amniotic fluid or chorionic villus sample to show only cells with normal chromosomes.

Mosaicism

Head and Brain

Many babies were born with a very large soft spot (fontanelle)

Where there are two different cell lines within the same tissue

or wide spaces between

the bony plates of the skull.

The front fontanelle was also often slow to close and in

Non-mosaicism

one child was still open at age 4.

So long as the parents have normal chromosomes, the extremely unusual sequence of

events that led to a fetus with tetrasomy 9p is very unlikely

Additionally, some babies have an unusual

head shape

to happen again.

When all the cells show tetrasomy 9p

or size (‘strawberry skull’; asymmetric head shape;

Many

couples will want the reassurance of having their next baby’s

Strabismus (squint) or short sight (myopia)

Dimple near the base of the spine

Sunken eyes due to eyeball being recessed within the orbit

Missing or underdeveloped bones

chromosomes tested

during pregnancy by chorionic villus sampling or

head; macrocephaly – large head;

microcephaly – small

amniocentesis.

Babies found to have mosaic tetrasomy 9p are likely to do better than those with non-mosaic tetrasomy 9p, especially in terms of survival beyond the newborn period.

Although these

techniques do not necessarily show tetrasomy 9p, a normal

result is reassuring.

Other medical concerns

Missing gallbladder

Umbilical hernia

Most likely features among those with mosaic tetrasomy 9p

Treatment List

What is the outlook?

Always seek professional medical advice about any treatment or change in treatment plans.

The outlook for babies diagnosed with tetrasomy 9p is extremely variable.

Developmental delay

A delay in expected development was the first sign of anything wrong.

Signs were first noticed b/w three months and early secondary school age.

Central nervous system (brain and spinal cord) anomaly

Abnormal features of arms or legs. These can include dislocated joints and clubfeet

Typical facial features including wide set eyes, small jaw (chin), oddly formed /positioned ears and a bulbous or beaked nose

People with tetrasomy 9p have two extra copies of material from the short (p) arm. They usually have two normal chromosome 9s as well, so they have four copies of 9p in all.

•Treatment varies considerable depending on the type and severity of symptom that develop

•Surgery may be needed to correct defects or abnormalities e.g. heart defects, skull and facial abnormalities

In some babies there is little or no effect on development or health, while in others the effects are obvious and sadly survival may not be possible.

Those babies diagnosed with non-mosaic tetrasomy 9p appear to be at greatest risk and typically do not survive the newborn period.

Minor anomalies of genitals

Can it be passed on?

Among boys with a mosaic tetrasomy 9p, eight (out of 19) and three girls (out of 22) were affected.

Thank

You!

Three boys were born with undescended testicles (cryptorchidism).

The testicles begin their descent from the abdomen during fetal life and have usually arrived in the scrotum by birth.

T

E

T

R

A

S

O

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by:

Pamela R. Rabano

When descent does not occur, the testicles can be brought down in a surgical operation and anchored in the scrotum.

BSMT III

Cytogenetics

Are there people with tetrasomy 9p who are healthy, have no major birth defects and have developed normally?

Size of isochromosome

The amount of extra chromosome material. Common sense suggests that those with larger extra chromosomes will be more severely affected.

normal

great majority of children with tetrasomy 9p have parents with

The

Specific duplicated regions

chromosomes.

But there are some people - and no-one really knows how many

of them there

•Access to programs and services as required e.g. physical therapy, speech therapy, educational support, social, vocational and medical services

•Various other symptomatic and supportive measures

•Genetic counseling and joining a support group is recommended

it.

- who themselves have tetrasomy 9p but are very mildly affected by

A boy with three copies of the section of chromosome 9 between band p13 and p22 shared some similarities with children with an isochromosome 9p, but had no major anomalies apart from enlarged ventricles within the brain. This could suggest that the part of 9p that he did not have extra copies of (9p23 to the tip of 9p) is the part that causes important birth defects.

They can pass it on.

They can also have normal children.

Spine

One man with tetrasomy 9p

had two children with normal chromosomes,

resulting in miscarriage.

but his wife also had five pregnancies

Eyesight Vision difficulties

A sacral dimple (dimple or hole in the skin just above the crease between the buttocks) is also sometimes seen but is six times as common in babies with non-mosaic tetrasomy 9p as in babies with the mosaic form.

Known difficulties include a squint (strabismus) (3), including exotropia (divergent squint), frequently intermittent, and lack

Tetrasomy 9p is usually found in highest concentrations in blood, so diagnosis in a baby, child or adult means taking and analysing a blood sample.

Confirmation and an estimation of the ratio of normal to tetrasomy 9p cells can use a sample of skin or a scraping from inside the cheek (buccal smear).

of stereoscopic vision (teaming of the eyes) causing loss of 3D vision

and depth perception.

The sacral dimple may be shallow so you can see the base, but stools can collect there before your child is toilet trained, so keeping it clean and protected is important.

Strabismus may be treated with patching, glasses, exercises or surgical

correction.

If there is any concern about this, your baby’s spine will be imaged, usually with ultrasound or an MRI scan.

Mosaic or not mosaic

When only tetrasomy 9p cells and no normal cells are found in both blood and skin cells or amniotic fluid, the effects are likely to be more obvious and more severe. Babies with mosaic tetrasomy 9p survive the newborn period better.

Tissue-limited mosaicism

Skeleton and bones

Feeding a child with Tetrasomy 9p

Feeding problems are common

The proportions of tetrasomy 9p cells are different in different body tissues. In blood there are more tetrasomy 9p cells and sometimes no normal cells are found. In other tissues, especially skin and mucous membranes, the proportion of tetrasomy 9p cells is usually lower and no tetrasomy 9p cells may be found. Organs, such as the brain and lungs, may have different proportions again and this variability is very likely to affect the outcome

Breastfeeding

By gastrostomy tube

Isochromosome

A variety of unusual features of the skeleton has been reported, including:underdeveloped shoulder blades

missing ribs

a prominent collar bone

underdevelopment of collar bones causing marked sloping of the shoulders

uneven skeletal growth with one side of the body larger than the other, a condition known as hemihypertrophy

Health concerns

An extra chromosome made up of two copies of the same part

Yes, there are. Out of 47 reports in the medical literature, there are three people with apparently normal development and a possible fourth.

One adult is an accountant and was discovered to have tetrasomy 9p when infertility was investigated.

Another adult was investigated for skin lesions.

Growth

Height and body build are variable

some adults short (5’ 1”/1.55m in a girl of 19 years)

others are of average height (5’ 9”/1.75m in a boy of 16 years;

5’ 11”/1.8m

in a boy of 15)

Another case is of a child who has developed normally to the age of five, although he showed growth delay before birth; a six-month-old baby also had no apparent abnormalities at the age of 6 months.

Behaviour

children and adults with tetrasomy 9p are loving,

caring individuals and generally speaking

have an open and sociable temperament

Kidneys

The kidneys were affected in more than one baby or child out of three with mosaic tetrasomy 9p.

*cystic kidneys

A multicystic kidney may be removed if it is causing discomfort.

The important thing is to ensure optimal function of the other kidney.

Development: sitting, moving, walking (gross motor skills)

late to achieve their ‘milestones’ of sitting and walking

- helped by regular physiotherapy

Why is tetrasomy 9p so variable?

Mobility is affected by abnormal muscle tone

- low tone (hypotonia)

- high tone (hypertonia)

Floppy to hold and have obvious head lag when held to sit

Improves with maturity and regular physiotherapy

Some achieve total mobility

Joint abnormalities

abnormalities of foot position

rocker bottom feet

pes cavus (‘claw foot’)

pes planus (flat feet)

(the feet are flat and stick out)

pes planovalgus

pes equinovarus (club feet, with the foot turned

inwards, the soles pointing towards each other)

where the toes point

pes adductus (so-called ‘banana foot’

inwards)

*specific physiotherapy

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