This article includes discussion of Kallmann syndrome, anosmic hypogonadism, dysplasia olfactogenitalis of de Morsier, hypogonadotropic hypogonadism and anosmia, Kallmann de Morsier syndrome, Kallmann syndrome 1, Kallmann syndrome 2, Kallmann syndrome 3, and olfactogenital syndrome. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Kallmann syndrome is a genetic condition manifesting hypogonadism and decreased ability to smell. Expressivity and penetrance are variable, accounting for considerable phenotypic and genetic heterogeneity. The first gene recognized, KAL1, is responsible for the X-linked form of the disease; KAL2 is responsible for the autosomal dominant form. In this article, the author presents new information from research studies in his discussions of the clinical manifestations, pathogenesis, genetics, epidemiology, and diagnosis of this syndrome.
• Kallmann syndrome is a heterogeneous genetic condition associated with mutations in KAL1 (X-linked), KAL2 (autosomal dominant), or several other genes under current investigation.
• The diagnosis may be suggested by the observation of micropenis or cryptorchidism in infancy, or delayed onset of puberty at a later stage; for this reason, diagnosis can be challenging early in the adolescent years.
• Affected individuals have variably deficient gonadal function, reduced ability to smell, and a wide variety of other changes.
Historical note and terminology
Kallmann syndrome is a genetic disorder in which hypogonadism (deficient function of gonads secondary to a deficiency in gonadotropin releasing hormone, or GnRH) is associated with decreased ability to smell (hyposmia or anosmia). This is often associated with hypoplasia or aplasia of olfactory bulbs and tracts, although rare individuals may have normal olfactory structures by MRI but may still be anosmic (Della Valle et al 2013). The condition was described by Kallmann and colleagues in 1944, although it was apparently recognized as early as 1856 (Kallmann et al 1944; DeMorsier 1954; Best et al 1990; Hardelin 2001). The genetic understanding of the condition continues to evolve. A gene responsible for the X-linked form of Kallmann syndrome was first discovered in a disease involving abnormal neuronal migration in the CNS (Rugarli and Ballabio 1993).
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