<prompt> In the following karyotype, what is the abnormality seen? Shows 2 X-chromosomes and 1 Y-chromosome.Gynecomastia with long thin limbsSho stature with polydactylyLoose connective tissue at nape of neckHigh-pitched crying  <response>: 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,XY47,XXY and 47,XXY48,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 hypogonadismClinical features : All these presentations are secondary to male hypogonadismLong lower limbsLower IQ level But no mental retardationGynecomastia Atrophied testes, small penis , male infeilityLoss 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 estradiolRef: Robbins 8e p165 