Klinefelter syndrome is the most commonly occurring sex-chromosome disorder, and it often goes undiagnosed. In this article the authors discuss the diagnosis and the clinical features and morbidities associated with Klinefelter syndrome. Treatments that improve the lives of patients, such as testosterone supplementation, are also reviewed. Klinefelter syndrome is the most common sex-chromosome disorder; it affects approximately one in every 660 men. This syndrome is characterized by the presence of one or more extra X chromosomes, and the karyotype 47,XXY is the most prevalent type. The 'prototypic' man with Klinefelter syndrome has traditionally been described as tall, with narrow shoulders, broad hips, sparse body hair, gynecomastia, small testicles, androgen deficiency, azoospermia and decreased verbal intelligence. A less distinct phenotype has, however, been described. Klinefelter syndrome is an underdiagnosed condition; only 25% of the expected number of patients are diagnosed, and of these only a minority are diagnosed before puberty. Patients with Klinefelter syndrome should be treated with lifelong testosterone supplementation that begins at puberty, to secure proper masculine development of sexual characteristics, muscle bulk and bone structure, and to prevent the long-term deleterious consequences of hypogonadism; however, the optimal testosterone regimen for patients with Klinefelter syndrome remains to be established.

Klinefelter syndrome in clinical practice.

Although clinical features in Turner syndrome have been well defined, underlying genetic factors have not been clarified. To deduce the factors leading to the development of clinical features, we took the following four steps: (1) assessment of clinical features in classic 45,X Turner syndrome; (2) review of clinical features in various female sex chromosome aberrations (karyotype-phenotype correlations); (3) assessment of factors that could lead to Turner features; and (4) correlation of the clinical features with the effects of specific factors. The results indicate that the clinical features in 45,X and in other female sex chromosome aberrations may primarily be determined by: (1) degree of global non-specific developmental defects caused by quantitative alteration of a euchromatic or noninactivated region; (2) dosage effect of a pseudoautosomal growth gene(s), a Y-specific growth gene(s), and an Xp-Yp homologous lymphogenic gene(s); and (3) degree of chromosome pairing failure in meiocytes that are destined to develop as oocytes in the absence of SRY.

Turner syndrome and female sex chromosome aberrations: deduction of the principal factors involved in the development of clinical features.

Klinefelter's syndrome and its variants: a hormonal and chromosomal study.

DURING the past decade several surveys have related the incidence of sex chromosome abnormalities among the general population with that among mentally deficient patients in hospital1–3. In 1963 Wegmann arid Smith4 carried out a buccal smear survey among a male population composed of juvenile delinquents and felons. They found the incidence of positive for sex chromatin lower (1 : 658) than in the neonatal population (1 : 377) and suggested that the XXY aberration does not contribute disproportionately to juvenile delinquency or felonious behaviour. Nevertheless, evidence is beginning to suggest that genetic factors influence criminal behaviour. Jacobs et al.5 have called attention to the criminal behaviour of males with the XYY sex chromosome complement.

Sex Chromosome Abnormalities

THE association between sex chromatin abnormality and mental sub-normality is well established. The incidence of sex chromatin abnormality in the new-born male and female population is about 0.2 per cent and 0.08 per cent respectively; in institutionalized mentally sub-normal male and female populations about 1 per cent and 0.4 per cent respectively. Court Brown1 reported that a high proportion of sex chromatin positive males recognized in his unit had been committed to a mental defective institution because of anti-social behaviour. He suggested that an abnormal sex chromosome complement might predispose to delinquency. However, a survey by Wegman and Smith2 on a group of socially disturbed males of relatively normal intelligence failed to show an increase in sex chromatin abnormality.

Sex chromosome abnormalities in two state hospitals for patients requiring special security.

A survey of sex-chromosome abnormalities among 4514 mental defectives.

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A survey of sex-chromosome abnormalities among 4514 mental defectives.