Down syndrome, Turner syndrome, and Klinefelter syndrome constitute the most common chromosomal abnormalities encountered by primary care physicians. Down syndrome typically is recognized at birth, Turner syndrome often is not recognized until adolescence,and many men with Klinefelter syndrome are never diagnosed.Click to see full answer. Furthermore, what is the difference between Down syndrome and Klinefelter syndrome?Down’s syndrome has its own dysmorphic findings and is accompanied by mental retardation and hypotonia. Klinefelter’s syndrome is a syndrome caused by a numerical abnormality that affects male physical and cognitive development.Secondly, what are Klinefelter and Turner syndromes examples of? Klinefelter syndrome is caused by the addition of an X chromosome. Normally, males have 46 chromosomes with one X and 1 Y chromosome. In the case of Klinefelter syndrome, the male has 2 X chromosomes and 1 Y chromosome (Figure 1). The presence of a Y chromosome is necessary for an individual to be male. Simply so, is Down syndrome XXY? With the discovery in 1956 that the correct chromosome number in humans is 46, the new area of clinical cytogenetic began its rapid growth. Several major chromosomal syndromes with altered numbers of chromosomes were reported, such as Down syndrome (trisomy 21), Turner syndrome (45,X) and Klinefelter syndrome (47,XXY).What causes Down syndrome and Turner syndrome?A number of genetic alterations are possible in TS. Monosomy: One X chromosome is completely missing. Experts believe this is caused by an error either in the father’s sperm or the mother’s egg. Every cell in the offspring’s body has one X chromosome missing.