The Kleine-Levin syndrome (see Chap. 128) is a rare disease comprising periodic hypersomnia, hyperphagia, and abnormal behavior frequently associated with sexual disinhibition (Table 125-2).31 This syndrome classically occurs in an adolescent man in his early 20s and vanishes in his 30s. The etiology and pathogenesis of the disease are unknown, although intermittent hypothalamic dysfunction has been proposed. Endocrinologic analysis, which has been carried out on a few patients, has revealed abnormalities of the HPA axis, and growth hormone and prolactin secretion during the symptomatic phase that normalized in the asymptomatic phase.32

The Prader-Willi syndrome is another rare syndrome characterized by congenital onset of hypotonia, childhood-onset hyperphagia and obesity, hypogonadism, mental retardation, and short stature (see Chap. 92) (see Table 125-2).33 This syndrome, which is associated with a deletion of the paternal chromosome 15, may represent a defect in early hypothalamic development. The hyperphagia is characterized by continuous eating as long as food is available, suggesting deficient satiety mechanisms. However, postprandial secretion of CCK is not impaired in patients with Prader-Willi syndrome.33 Furthermore, serum leptin levels and adipose tissue leptin mRNA have not been found to differ between children with Prader-Willi syndrome and obese nonsyndromal children.34