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Kallmann syndrome is a disorder of hypogonadotropic hypogonadism, delayed puberty, and anosmia.
Hypogonadotropic hypogonadism (HH) occurs when the body does not produce enough of two important hormones, luteinizing hormone (LH) and follicle stimulating hormone (FSH). This results in underdeveloped gonads and often infertility. Anosmia, the inability to smell, was first described with hypogonadotropic hypogonadism in 1856, but it was not until 1944 that Kallmann reported the inheritance of the two symptoms together in three separate families. Hence, the syndrome of hypogonadotropic hypogonadism and anosmia was named Kallmann syndrome (KS).
Kallmann syndrome (KS) is occasionally called dysplasia olfactogenitalis of DeMorsier. Affected people usually are detected in adolescence when they do not undergo puberty. The most common features are HH and anosmia, though a wide range of features can present in an affected person. Other features of KS may include a small penis or undescended testicles in males, kidney abnormalities, cleft lip and/or palate, clubfoot, hearing problems, and central nervous system problems such as synkinesia, eye movement abnormalities, and visual and hearing defects.
Most cases of Kallmann syndrome are sporadic. However, some cases are inherited in an autosomal dominant pattern, an autosomal recessive pattern, or an X-linked recessive pattern. In most cells that make up a person there are structures called chromosomes. Chromosomes contain genes, which are instructions for how a person will grow and develop. There are 46 chromosomes, or 23 pairs of chromosomes, in each cell. The first 22 chromosomes are the same in men and women and are called the autosomes. The last pair, the sex chromosomes, are different in men and women. Men have an X and a Y chromosome (XY). Women have two X-chromosomes (XX). All the genes of the autosomes and the X-chromosomes in women come in pairs.
Autosomal dominant inheritance occurs when only one copy of a gene pair is altered or mutated to cause the condition. In autosomal dominant inheritance, the second normal gene copy cannot compensate, or make up for, the altered gene. People with autosomal dominant inheritance have a 50% chance of passing the gene and the condition onto each of their children.
Autosomal recessive inheritance occurs when both copies of a gene are altered or mutated to cause the condition. In autosomal recessive inheritance, the affected person has inherited one altered gene from their mother and the other altered gene from their father. Couples who both have one copy of an altered autosomal recessive gene have a 25% risk with each pregnancy to have an affected child.
X-linked recessive inheritance is thought to be the least common form of inheritance in KS, but is the most well understood at the genetic level. With X-linked recessive inheritance, the altered gene that causes the condition is on their X chromosome. Since men have only one copy of the X chromosome, they have only one copy of the genes on the X chromosome. If that one copy is altered, they will have the condition because they do not have a second copy of the gene to compensate. Women, however, can have one altered copy of the gene and not be affected as they have a second copy to compensate. In X-linked recessive conditions, women are generally not affected with the condition. Women who are carriers for an X-linked recessive condition have a 25% chance of having an affected son with each pregnancy.
Though all three patterns of inheritance have been suggested for Kallmann syndrome, as of 2001 only one gene has been found that causes Kallmann syndrome. The gene, KAL, is located on the X chromosome and is responsible for most cases of X-linked recessive Kallmann syndrome. The gene instructs the body to make a protein called anosmin-1. When this gene is altered in a male, Kallmann syndrome occurs. Of those families who have an X-linked recessive form of KS, approximately 1/2 to 1/3 have identifiable alterations in their KAL gene.
Author Info: Carin Lea Beltz, MS, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Genetic Disorders Part I, 2002
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