In the following karyotype, what is the abnormality seen? Shows 2 X-chromosomes and 1 Y-chromosome.

Klinefelter syndrome Genetic mechanism: Due to nondysjunction of either maternal or paternal X gene during meiosis, the male fetus will inherit one Y chromosome and more than one X chromosome. Remember, the chance of getting an extra X chromosome from the father or the mother is equal. Karyotype: 47XXY (common). Mosaics like 46,XY/47,XXY and 47,XXY/48,XXY are also seenPathogenesis: Except one X chromosome in the fetus all the other X chromosomes bears an active androgen receptor (that is represented shoest CAGrepeats). The shoer the CAG repeats, moreactive the receptor is. Since the X chromosomes were inactivated, the fetus develop "hypogonadism"Clinical features : (All these presentations are secondary to male hypogonadism)*Long lower limbs*Lower IQ level (But no mental retardation)*Gynecomastia *Atrophied testes, small penis , male infeility*Loss of secondary sexual characteristics like deep voice, beard and male distribution of pubic hair. Other associations :*Type 2 diabetes , metabolic syndrome and mitral valve prolapsedLab findings : *FSH elevated, testosterone reduced and increased estradiol(Ref: Robbins 8/e p165)