Change in chromosome structure or number other than the normal 23 pairs of chromosome are called as chromosome abnormality. In 23 sets of chromosome 22 sets are autosomal chromosomes that are they code for the proteins which are responsible for our behaviour, reaction to a particular situation and also our physical attributes. Remaining 1 set of chromosome are sex chromosomes they determine the sex of an individual. Abnormalities in these sex chromosomes lead to some genetic disorders.
Sex chromosome abnormalities are fairly common but the effect of these abnormalities is less severe than the effect caused by autosomal abnormality. Sex chromosome abnormalities cause learning disability or physical abnormality, and sex chromosome abnormalities are detected coincidentally during studying the cause for infertility or at amniocentesis.
Turner syndrome is a genetic condition caused by the loss of one of X-chromosome; as a result female conception occurs with 45 chromosomes. Live birth female infants with this condition are 1 in every 2500. Phenotypic abnormalities vary considerably; most common features are short stature, infertility, broad chest and neck webbing. Turner syndrome is also associated with some of the autoimmune diseases like thyroiditis, hypertension, obesity and non-insulin dependent diabetes. Not only loss of whole X-chromosome but also the abnormalities like deletion or rearrangements can also induce genetic condition called as Turner syndrome.
Triple X Syndrome:
The additional X-chromosome causes a condition known as triple X syndrome. The diagnosis of this condition is coincidental; additional X chromosome usually arises as a result of nondisjunction error occurred during meiosis I in egg (maternal meiosis). The triple X syndrome has an incidence rate of 1 in 1200 live born female infants. Affected girls are usually taller than average, they face educational problems and also some delay with motor and language development. Most of the females with this condition are fertile and deliver normal offspring.
Klinfelter syndrome is seen in males. Klinefelter syndrome with karyotype XXY, (that is three sex chromosomes present instead of normal two sex chromosomes) occur with an frenquency rate of 1 in 600 livebirth male infants. This syndrome is a result of nondisjunction and the additional X chromosome arises from either maternal or paternal side. Diagnosis of this syndrome is coincidental. The main physical syndrome of this genetic condition is hypogonadism. Hormone replacement therapy with testosterone is used as a treatment for affected infertile males. Klinfelter syndromemay also induce gynaecomastia in affected males. The risk of breast cancer incident is higher in Klinfelter syndrome males when compared to normal XY males. Educational difficulties, behavioural disturbance are some of the commom problems associated with Klinfelter syndrome.
XYY syndrome is also seen in males, occurs due to nondisjunction of chromosome occurred in paternal meiosis II. XYY syndrome occurs with incident rate of 1 per 1000 live born male children. Males with XYY syndrome do not show any major clinical abnormalities; as a result in most of the cases this abnormality is undiagnosed. Accelerated growth rate is seen during early childhood; as a result males with this condition are taller than the normal males.
XYY syndrome may result in behavioural problems like hyperactivity, distractibility and impulsiveness.
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