What is a chromosome disorder and what is its significance?
Chromosomes are the structures
in which our hereditary material (DNA) is packed.
A healthy person has 46 chromosomes (23 pairs). One chromosome of each pair (i.e.
a total of 23 chromosomes) is donated by each parent to the fetus. Twenty-two pairs
are called autosomes, and the 23rd pair consists of the sex chromosomes (X and Y).
Females have two X chromosomes and males have one X and one Y. The chromosome pairs
are arranged and numbered by size and shape, and each has different genes. Because
there are two copies of each chromosome, there is effectively a duplicate gene system
(one maternal and the other paternal), each identical in sequence to the other.
A change in the number or structure of the chromosomes in pairs 1 - 22, causing
an addition or deletion of chromosomal information in these pairs compared with
the normal state, constitutes a significant medical problem. In the great majority
of cases, this change is expressed as severe structural or functional defects in
the tissues and/or mental retardation. For example, an extra number
21 chromosome, resulting in three instead of the normal two so that there are 47
chromosomes altogether, causes Down
syndrome. An extra number 18 chromosome, which is larger and therefore contains
more genes, manifests as a more severe disorder called Trisomy 18. In this syndrome, there are severe defects,
and it usually ends in death soon after birth or even in the uterus. This is also
the case with a deletion of the whole or a part, however small, of chromosome 18.
Conversely, the clinical manifestation of a change in the number of sex chromosomes
(X or Y) or their structure, as is the case in XYY syndrome, is usually less severe.
What is XYY syndrome?
This is the name given to the syndrome resulting from an extra Y chromosome in males.
Normally males have one X and one Y chromosome, but a male with this condition has
an extra Y chromosome, so that he has 47 chromosomes altogether.
The frequency is estimated to be about 1 in 1000 male births, and externally boys
with this condition do not appear to be different from normal.
The only characteristic physical feature is tall stature compared to other family
They also have a somewhat aggressive tendency.
Studies have shown that many XYY males have completely normal intelligence, but
on average there is a decrease in their level of achievement, delay in speech development,
and some have learning disorders. Some of these children have also been found to
have additional problems such as hyperactivity, attention deficit disorders, over-impulsiveness
and other adjustment disorders. Behavioral problems such as aggressiveness impede
It is important to emphasize that in this syndrome there are no external characteristics
or fertility problems that point to the diagnosis - however, behavior problems such
as aggressiveness and/or learning disorders are part of the syndrome. The only way
to identify these children is by prenatal diagnosis or performing chromosome analysis
after birth. Studies of the frequency of sex chromosome disorders in newborns indicate
that there are many more children with XYY syndrome in the population than are diagnosed,
which suggests that a significant proportion of them are normal and remain undiagnosed.
Most studies of XYY syndrome have included only small numbers of patients, and therefore
it is difficult to assess accurately the exact risk of behavioral problems, and
whether psychological intervention and an appropriate environment can reduce this