Genetics and Kallmann Syndrome & Congenital Hypogonadotropic Hypogonadism.

 

The genetics of Kallmann syndrome is a complex and ever changing picture. Puberty is a major step in the development of any animal so it is no surprise that there are many different genes involved in the instigation of puberty and continuation of the reproductive function.

There have been so far 25 different genes that have been identified in causing cases of KS or CHH. Even taking there 25 genes into consideration approximately 50% of cases of KS / CHH still have an unknown genetic origin. 

These genes cover all modes of inheritance, so if a person has KS / CHH there is a chance that they can pass it on to any offspring if they undergo fertility treatments. Due the the nature of the genes involved it is almost impossible for doctors to be able to predict the chances of passing on KS / CHH unless there is a strong family history of the condition.

Even if the case has occurred sporadically or in isolation within a family it can still be passed on.

For some genetic conditions, such as Turner syndrome or Klinefelter syndrome the diagnosis is straightforward as there is a variation in the number of chromosomes present. A simple test called a karyotype can be performed to see the number of chromosomes present and if there is a X and Y chromosome present if the patient is male or two X chromosomes present if the patient is female.

Other genetic conditions are caused by single gene errors. In this case tests are done at the chromosomal level to identify specific genes within the chromosome to see if they are missing or damaged in some way.

With KS / CHH the picture is less clear. The vast majority of patients with KS / CHH are born with the normal assignment of chromosomes so the karyotype test will come back as normal. Also there is no one specific gene to look for and the gene defect might be so small it might be difficult to spot. A defect could be as small as two letters missing or in the wrong place in a book of 1,000 pages.