Klinefelter syndrome - Genetic syndromes: Patterns of inheritance

Klinefelter syndrome

Definition

Chromosomal abnormality with a genotype 47XXY.

Incidence

1 in 1000 males.

Age

Congenital.

Sex

Phenotypically males.

Aetiology/pathophysiology

In 80–90% there is a 47XXY karyotype, the extra X coming from the mother. 48XXXY and 49XXXXY karyotypes are usually associated with mental retardation, i.e. the more X chromosomes the more severe the phenotype. Many cases go undetected as patients are generally normal. All appear normal until puberty when hypogo-nadism becomes prominent.

Clinical features

Tall, with long arms and legs, hypogonadism, female pubic hair profile, highpitched voice, reduced facial and body hair. Other features that may be present include gynaecomastia. There is greatly reduced fertility, slight but significant reduction in IQ.

Investigations

Karyotype analysis.

Management

Testosterone replacement should be given during adolescence for psychosexual development and prevention of osteoporosis.