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We’ve put together some basic information about chromosomes to help clarify what Zoe has.
What are Chromosomes?
Chromosomes are the structures that hold our genes. Genes are the
individual instructions that tell our bodies how to develop and keep
our bodies running healthy. In every cell of our body there are 20,000
to 25,000* genes that are located on 46 chromosomes. These 46
chromosomes occur as 23 pairs.
We get one of each pair from our mother in the egg, and one of each
pair from our father in the sperm. The first 22 pairs are labelled
longest to shortest. The last pair are called the sex chromosomes
labeled X or Y. Females have two X chromosomes (XX), and males have an
X and a Y chromosome (XY). Therefore everyone should have 46
chromosomes in every cell of their body. If a chromosome or piece of a
chromosome is missing or duplicated, there are missing or extra genes
respectively. When a person has missing or extra information (genes)
problems can develop for that individual's health and development.
Each chromosome has a p (the short) arm and q (the long) arm. Some of
the chromosomes like 13, 14, and 15 have very small p arms.
Each chromosome arm is defined further by numbering the bands, the
higher the number, the further that area is from the centromere (the
region that separates the two arms).
Chromosomes are flexible structures made up of DNA. The coding order of that DNA makes up the genes.
How do chromosomal abnormalities occur?
Most chromosome abnormalities occur as a accident in the egg or sperm.
Therefore every cell in the body would have the abnormality.
Chromosome abnormalities can be inherited from a parent, like a
translocation. In that case, if a person has a balanced translocation
of his/her genes – that is, where bits of parts of chromosomes
have broken off and switched places, but because all the material
needed is present but just switched around (translocated), they
pose no health problems. The problem only arises when the person has
children.
Chromosome abnormalities can be be 'de novo' – that is, new in
that individual – and happen after conception, and individuals
can have a mosaicism (some cells with the abnormality and some without).
What does Zoe have?
Zoe has 47,XX,dup(15)(pter-q15) or what is called a partial Trisomy of Chromosome 15*.
Below is an actual image of Zoe's chromosomes. You'll see she has an
extra piece of chromosome with the chromosome 15 pair.
This means that she has a duplication of chromosome 15 involving the
bands from the terminus end of the p arm to q15. She does not have
mosaicism.
*What
we learnt a couple of months later is that Zoe also has a bit of
Chromosome 7 attached to the 15, which is likely to have added
health/developmental implications.
What is a chromosome duplication?
A duplication is a duplication of a section of a chromosome. It is
sometimes called referred to as a 'trisomy'. Trisomy refers to three.
Therefore if a duplication exists, that individual has three copies of
that area instead of two. This means there are extra instructions
(genes) present that can cause an increased risk for birth defects or
developmental problems.
What does this mean for Zoe?
Additional chromosomal material upsets the intricate delicate balance
of cell functions needed for normal development. The "dosages" are
disrupted.
From what we’ve been told, q11-13 are critical areas in chromosome 15.
Prader-Willi and Angelman’s syndromes are the
“common” outcomes of those affected by chromosome 15q11-13.
Zoe does not present as either. From what we have been reading, Zoe
seems to fit more with another group called “idic15”.
Although the geneticist has not confirmed that, we feel that the
descriptions seem to match what Zoe is displaying much closer. We
showed the geneticist a list of probable physical/health problems
associated with chromosome 15q duplications (taken from an idic15
website), and he agreed with it.
A summary of the list follows. Zoe has mild to moderate symptoms of many of the following but not the autistic
behaviors (which we are hoping to help her avoid!). The information was taken from the idic15 website and you can find the full details by going to: www.idic15.org
Physical issues
Unlike many other chromosomal syndromes (eg. Down's syndrome), there
are few characteristic physical findings associated with chromosome 15q
syndrome. The physical findings are fairly non-specific and may include
the following:
Hypotonia:
Babies with dup15q usually have hypotonia (poor muscle tone). Motor
milestones such as rolling over, sitting up, and walking are
significantly delayed. Older children and adults with hypotonia often
tire easily. Hypotonia in dup15q syndrome generally decreases with age
and sometimes progresses to hypertonia (tight muscle tone),
particularly in the lower legs.
Physical features:
Many children with dup15q share similar facial characteristics. These
include a flat nasal bridge which gives them a 'button' nose. The palate (roof of the mouth) may be unusually high. There are
also reports of areas of increased and reduced skin pigmentation.
Growth: body growth is retarded in about 20 – 30% of individuals with dup15q, but head growth is typically in the normal range.
Other Abnormalities:
Rarely, babies with dup15q may be born with a cleft lip and/or palate
or differences in the way their hearts, kidneys, or other body organs
are formed. For this reason, it is important for newly diagnosed
children with dup15q to be carefully evaluated for the possibility of
such structural differences.
Developmental issues
Gross Motor Delays:
Due to the hypotonia experienced by young children with dup15q
syndrome, gross motor delays are very common. The vast majority of
people with dup15q are able to walk independently although some degree
of ataxia (coordination problems) may be apparent.
Fine Motor Delays:
Parent report suggests that fine motor delays are widespread among
children with dup15q syndrome. Nonfunctional use of objects with an
immature type of exploration has been reported in the scientific
literature.
Cognitive Delays:
Most individuals with dup15q syndrome show some degree of cognitive
delay/disability from very early on. These
cognitive disabilities are often associated with behavioural problems
as children age.
Autism Spectrum Disorders:
There are now over 20 reports in the literature of individuals with
both autism and idic(15).
Chromosome 15q11 – 13 duplications are the most frequently identified chromosome problem in individuals with autism.
Speech/Language Delays:
Most children with dup15q are affected by speech/language delays.
Expressive language may be absent or may remain very poor, and is often
echolalic with immediate and delayed echolalia and pronoun reversal.
While the majority of children with dup15q experience speech delays, a small subset of children are highly verbal.
Sensory Processing Disorders:
Parent report suggests that sensory processing disorders are widespread
in dup15q syndrome. These sensory processing disorders disrupt the
affected child’s ability to achieve and maintain an optimal range
of arousal and to adapt to challenges in daily life. These disorders
are often manifested by an over-responsiveness or under-responsiveness
to sensory input or fluctuations in response to sensory input.
Behaviour Challenges:
Many children with dup15q have difficulties of behaviour and social
communication, with a lack of response to social cues frequently
observed.
Medical issues
Seizure Disorders:
Seizures represent an important medical feature of dup15q syndrome.
Over half of all people with idic(15) will have at least one seizure.
The majority of those will experience their first seizure before age 5,
but seizure onset occurs up through puberty and young adulthood in this
population.
Attention Deficit Disorders: Attention Deficit Disorder/Hyperactivity has been reported in a number of cases of children with dup15q syndrome.
Anxiety Disorders: Parent report of anxiety disorders in children with dup15q syndrome has been noted.
Other Medical Problems:
Other reported medical problems include recurrent respiratory
infections in childhood, middle ear effusions requiring tubes, eczema,
precocious puberty, other menstrual irregularities, overeating and
weight gain. Scoliosis is also reported in adolescence.
How we are approaching this diagnosis
We are going through the emotions that flood any parents' minds and
hearts when they receive any bad news about their child. Denial, anger,
fear, guilt, and hopelessness are the few major ones.
However, while this diagnosis came as a shock, we seem to be going
through the gamut of emotions at a quicker pace. Possibly because this
is not the first time we’ve had such news with regard to Zoe.
Being told that she had Cerebral Palsy in October 2006 was a shot in the
heart.
If nothing else, being told that Zoe has a chromosomal abnormality has
given us an answer to why she is developmentally delayed. Although the
list above looks bleak and daunting, most of them are a list of
“maybe”s. The more intensive therapies we give her now, the
better the odds.
It galvanises us to seek all the ways to help her.
Zoe is a very resilient and determined little girl. And with our total love and support, there is no limit to her potential.
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