Late puberty in boys may be genetic

​In a comprehensive study of 1130 Danish boys and 424 Chilean boys, a group of researchers headed by Professor Anders Juul from Rigshospitalet has found two new genes which may help explain why some boys reach puberty later than others.

​Danish boys typically reach puberty between the ages of 9 and 14. There is great variation in when individual boys go through puberty, but it is a well-known fact that they are reaching puberty at an ever earlier age.

For many years, researchers have tried to find the reasons behind this trend of earlier puberty in both boys and girls, but the mystery has yet to be solved. This also applies for late puberty, which is seen most frequently in boys. For many years, focus has been on environmental factors, but this new research from Rigshospitalet shows that puberty in boys is also genetically determined. Therefore, we now know more about which genes help stimulate puberty, but also which genes can delay puberty. 

"We already know about 389 genes in girls which affect puberty, but we only know of 9 genes in boys," explained Alexander Busch, physician and PhD student from the Department of Growth and Reproduction, who headed the study.

"With this study, we found the 10th and 11th genes that may help explain the timing of puberty in boys. A special variant within these genes may contribute to delaying the onset of puberty," he explained. 

The researchers at Rigshospitalet have discovered that the genes for the important sex hormone FSH (FSHB) and its receptors (FSHR) play a major role in determining when boys reach puberty. FSH and FSHR belong to an endocrine system which has its starting point in the pituitary gland of the brain, and hormone production by the pituitary gland is essential for sperm production in boys and for the oestrogen production in girls’ ovaries.

In the study, the researchers compared 1130 Danish boys with 424 Chilean boys. The comparison showed that the Chilean boys reached puberty earlier than the Danish boys. As many as eight months earlier on average. The Chilean boys had a much higher BMI than the Danish boys, but the researchers have corrected data for this factor and can demonstrate that differences in BMI do not determine early puberty. Instead, there proved to be a genetic explanation to the significant difference in ages for puberty. The activity of the endocrine system is lower in boys with a specific genetic variation in the two newly discovered genes, and this seems to cause the testicles to mature more slowly than in other boys. 

Important knowledge in treatment of late puberty

This new knowledge about the gene variation may help explain why some boys reach puberty later than others, and could have a significant impact in clinical practice", said Dr. Busch. 

"If we're contacted by the family of a boy who has not reached puberty at the age of 16, we often see that the father was also a late bloomer in his youth. This stresses the congenital component of the timing of puberty. The problem is that we don't know whether such a boy will reach puberty in three months, or if he will never go through puberty. In future, we can carry out a gene test that will show whether the boy's DNA is part of the explanation so there isn’t as much cause for concern," explained Professor Juul. 

"In such cases, we would monitor the boy over the next few months to see whether his testicles start to grow on their own. If not, we can offer treatment with testosterone, for example. Fortunately, in most cases treatment is not necessary for absent puberty," he said.

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