47,XXY Library Resources
Brief Introduction to 47,XXY
In 1942, a young doctor by the name of Harry Klinefelter was assigned to work with Dr. Fuller Albright – commonly considered to be the father of endocrinology – at Massachusetts General Hospital in Boston. During the course of his fellowship, Dr. Klinefelter examined and subsequently prepared a case study concerning nine adult men with a common set of symptoms. Dr. Albright encouraged his young associate to be the lead author on the study, which was published in the November 1942 issue of The Journal of Clinical Endocrinology, and the combination of symptoms that Dr. Klinefelter described therein has since been referred to as “Klinefelter syndrome.”(1)
Over 14 years after Dr. Klinefelter published his case study, in 1956, Drs. Joe Hin Tjio and Albert Lavan confirmed that there were 23 pairs of chromosomes in humans. Up until that time, it had been thought that there were 48 chromosomes, but using a more advanced experiemental methodology, Tjio and Lavan were able to confirm that there were, in fact, only 46 chromomsome.(2) This discovery by Tjio and Lavan is generally considered to be the beginning of modern “cytogenetics,” which is the study of chromosomes and the diseases caused by either numerical and/or structural abnormalities in them.
Three years later, in 1959, a young English researcher named Patricia Jacobs and her associate published a study correlating 47 chromosomes - that is one more than commonly found in humans - with Klinefelter syndrome.(3) Because the extra chromosome Dr. Jabobs discovered was an extra X, the karotype for an individual born with this aneuploidy condition is referred to as “47,XXY.”
Are 47,XXY and Klinefelter syndrome the same thing?
If all persons with the set of symptoms described by Dr. Klinefelter had an extra X chromosome, or if all persons born 47,XXY had the symptoms described by Dr. Klinefelter, then the two terms would be interchangeable. However, this is not the case. Consider the following two questions -
Does everyone with Klinefelter syndrome have an extra X chromosome? The answer is “No.” In 1985, Dr. Klinefelter published an article in which he summarized what had been learned about the condition during the more than 40 years since his having first identified the condition. Dr. Klinefelter wrote: “the syndrome has been found to be a chromosomal disorder, in which there is an extra X chromosome in 80% of the patients.” (4)
Does everyone born with an extra X chromosome have Klinefelter syndrome? This answer is “No.” Females born with an extra X chromosome are Trisomy X; and while all males who are born with an extra X chromosome are at risk of developing Klinefelter syndrome, for currently unexplained reasons, there is broad phenotypic variability and many of these 47,XXY inviduals may not develop one or more of the distinguishing signs and symptoms of the condition.
According to the latest estimates, the incidence level of 47,XXY is approximately 1 out of 500 live birth males. (5)
Resources for XXY and Klinefelter Syndrome
Answers to Frequently Asked Questions related to 47,XXY (Printable PDF)
INTERACTIVE FAQ (note: be sure to apply condition filter "47,XXY" to eliminate extraneous Q&A)
GUIDEBOOK: Living with Klinefelter Syndrome (47,XXY) Trisomy X (47,XXX) and 47,XYY:
A Guide for Families and Individuals Affected by Extra X and Y Chromosomes
Understanding Klinefelter Syndrome: A Guide for XXY Males and Their Families
(National Institutes of Health)
en español* translations were performed by volunteers, While every effort was made to ensure accuary, KS&A is not responsible for unintended errors.
Resources for Klinefelter Syndrome
(National Center for Biotechnology Information)
(American Academy of Family Physicians)
The Learning Needs of Boys with KS: Information for Parents and Teachers
This online guide was prepared by Klinefelter Syndrome Associates (in the UK) for teachers and classroom assistants of boys who have a previous diagnosis of Klinefelter syndrome.
(1) Harry F. Klinefelter, E. C. Reifenstein and Fuller Albright, “Syndrome Characterised by Gynecomastia, Aspermatogenesis with A-Leydigism, and Increased Excretion of Follicle Stimulating Hormone,” Journal of Clinical Endocrinology, 1942, 2: 615-627.
(2) Joe Hin Tjio and Albert Levan, “The Chromosome Number of Man,” American Journal of Obstetrics and Gynecology, 1956, 130:723-724.
(3) Patricia A. Jacobs and J. A. Strong, “A Case of Human Intersexuality Having a Possible XXY Sex-determining Mechanism,” Nature, 1959, 183: 302-303.