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Kallmann syndrome is considered to be a rare condition. Precise epidemiological data is lacking due to difficulty with the diagnosis of the condition and the acquisition of accurate data about the condition.
Males are more likely to be affected than females. This is thought to be linked to the X-linked inheritance pattern of Kallmann syndrome type 1, as well as a higher tendency to seek medical help when sexual development fails to take place in males.
A retrospective study recently conducted in Finland found that the incidence of Kallmann syndrome was at least 1 in 48,000 newborns. Baby boys were much more likely to be affected, with an incidence of 1 in 30,000, compared to the incidence in girls of 1 in 125,000.
According to a study of French conscripts, the incidence of Kallmann syndrome was approximately 1 in 10,000 men. A study of Sardinian military recruits found the prevalence of hypogonadism associated with Kallmann syndrome was approximately 1 in 86,000 men.
Based on the studies outlined above, the prevalence of Kallmann syndrome is estimated to be 1 in 8,000 males and 1 in 40,000 female. However, it is likely that this is an underestimation due to difficulties in the diagnosis of the condition, and gross variation in the phenotypic presentation of the syndrome, especially for females.
Although Kallmann syndrome is present from birth in most individuals, the diagnosis is not usually made until the age of puberty, and is then prompted by the lack of sexual development. However, it is sometimes diagnosed earlier in males due to signs such as cryptorchidism and micropenis.
Males are more likely to be affected, with a male: female ratio of about 4:1. This susceptibility of men to Kallmann syndrome can be explained in part by the genetic inheritance pattern, and may also be related to an increased tendency on the part of males to seek medical advice when puberty is delayed. It follows an X-linked recessive inheritance pattern, which means that a male child only needs to inherit one mutated ANOS1 gene from the mother to be affected, whereas females need to inherit gene mutations on both X-chromosomes to develop the syndrome.
The complications associated with Kallmann syndrome can have an impact on the quality of life of the affected individual, as they affect both physical appearance and functioning of the body in the area of sexual maturation, and thus threaten psychological health.
There is no change in long-term survival rates for most patients unless they are affected by other health conditions, such as congenital heart disease or neurological manifestations. Complete adrenocortical insufficiency is one linked condition, though in rare cases, which can be fatal if it is not diagnosed and treated promptly.
Deficiency in gonadotropin-releasing hormone (GnRH) production or release can sometimes present later in life, after the individual has already passed the age of puberty as normal. This is associated with symptoms of decreased libido and infertility, although the major pubertal body changes have already occurred. Individuals with a family history of GnRH deficiency are more likely to be affected by Kallmann syndrome, when contrasted with the incidence of the general population, which is less than 1%.