Marhaba Niazi
Assignment
14-10474
 Isodicentric Chromosome 15 Syndrome:
Individuals with isodicentric chromosome 15, or "idic15", have 47 chromosomes instead of the
typical 46 chromosomes. Occasionally, a person may have 2 extra idic15 pieces (48
chromosomes) or 3 extra idic15 pieces (49 chromosomes) in all or some of their cells. When the
extra genetic material comes from the paternal chromosome, a child may have normal
development. However, when the duplicated material comes from the maternal chromosome,
developmental problems are often the result. Most commonly, the region called 15q11-q13 is the
portion of chromosome 15 duplicated. Individuals with idic15 usually have a total of four copies
of this chromosome 15 region instead of the typical two copies (1 copy each on the maternal and
paternal chromosomes and 2 copies on the idic15).
Some children and adults with idic15 are said to have 'mosaicism', meaning that their extra 15th
chromosome is present in some, but not all, of their body cells.
How often it occurs?
Researchers think that approximately 1 in 8,000 babies are born with an extra chromosome that
came from chromosome 15. The most common type of marker chromosome 15 is very small and
does not cause any problems. Generally, people with idic15 do not have family members with
the chromosome abnormality. The idic15 usually forms by chance in one person in the family.
Symptoms:
Since chromosomes carry genes that determine how our bodies grow and develop, having extra
chromosomal material can alter a person’s
physical and mental development. There is also
a wide range of severity, so that two children
with the same chromosome pattern may be very
different in terms of their abilities. In general,
the following features are found in most people
with idic15 to varying degrees:
i. Poor Muscle Tone (hypotonia)
particularly in babies, with delayed
milestones (although the vast majority
will walk independently),
ii. Cognitive Disabilities/Learning
Disabilities
iii. Autism Spectrum Disorders
iv.
Seizure Disorders
v. Speech/Language Delay
vi.
Sensory Processing Disorders
vii.
Attention Deficit Disorders
(ADD/ADHD)
viii. Anxiety Disorders
ix. Small size for age
Marhaba Niazi
x.
Assignment
14-10474
Minor unusual physical features, including wide-spaced eyes with skin folds at the inner
corners (epicanthal folds); noticeable unfolding of the edge of the ears; short, upturned
nose with a low or flattened nasal bridge; and full lips.
Isodicentric Chromosome 15 and Autism
Research studies of individuals without chromosome anomalies also support this idea that an
autism-related gene may be present in 15q11-q13. Specifically, research studies found that
certain DNA markers from the 15q11-q13 region were found more often in individuals with
autism than in individuals without autism. Although these DNA markers are too small to be
genes, they suggest that researchers may be getting close to finding an autism gene in this region.
Researchers are currently focusing on genes in this region called the GABA receptor genes,
known as GABRB3, GABRA5, and GABRG3. They are good candidates for being related to
autism not just because of their location, but also because of their function. The GABA genes
make proteins that carry messages between nerve cells. Several studies have found associations
between GABRB3 and autism1 .
How common is isodicentric chromosome 15 syndrome?
This syndrome occurs in about 1 in 30,000 newborns.
Can it be inherited?
It is not inherited usually and occurs as a random event in the production of reproductive cells of
one of the parents of the effected individual.
Diagnosis:
Karyotyping is used for the testing and FISH is used for the confirmation of diagnosis for this
chromosomal abnormality.
1
Buxbaum et al., 2002; Shao et al., 2003; Cook et al., 1998.