Kallmann syndrome

Last revised by Francis Fortin on 6 Apr 2022

Kallmann syndrome is a rare genetic disorder characterized by hypogonadotropic hypogonadism associated with anosmia or hyposmia. When anosmia is absent, a similar syndrome is referred to as normosmic idiopathic hypogonadotropic hypogonadism. 

It is a rare disorder with an estimated prevalence of one in 10,000 males and one in 50,000 females 1,3. Both clinically and genetically Kallmann is heterogeneous, and although most cases are sporadic, all modes of inheritance have been described 1,3.

Although patients with Kallmann syndrome are anosmic from birth, this usually is not apparent to either the parents or the child. The diagnosis is only made when puberty does not occur. At that time gonadotropin levels (FSH and LH) and sex hormones (testosterone and estradiol) are low, whereas other pituitary hormones are normal 3

Occasionally the diagnosis is made earlier due to investigation of other associated anomalies, including:

Kallmann syndrome is a genetic condition with multiple implicated genes 4. The most common of these is the ANOS1 (formerly KAL1) gene, which is inherited in an X-linked recessive pattern; however, there are other genes that may be inherited in autosomal patterns 4. It is thought that mutation of this gene, and other similar genes, results in failure of appropriate migration of gonadotropin-releasing hormone-secreting cells and olfactory neurons during embryogenesis 4.

MRI is the modality of choice in assessing for the absence of olfactory bulbs, and coronal T2 sequences are most effective. The olfactory nerves, bulbs, and sulci are absent (arhinencephaly).

Importantly the hypothalamus and pituitary are most often morphologically normal in appearance. However, the anterior pituitary can appear small. 

Treatment is primarily aimed at restoring normal pubertal development and in some cases normal fertility. The former can be achieved by administration of exogenous sex steroids, appropriate to the gender of the patient. If fertility is desired, pulsed gonadotropin-releasing hormone can be administered (with variable success) 3

It was first identified as a clinical entity by Franz Josef Kallmann, a German-born American psychiatrist, in 1944 5, although may have been first reported nearly a century prior by Maestre de San Juan in an 1856 case report 6.

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