Short Sleeper

A number sign (#) is used with this entry because the natural short sleep phenotype is caused by mutation in the DEC2 gene (BHLHE41; 606200).

Description

In a review of various classification schemes for sleep disorders, Thorpy (1990) listed 'short sleeper' under the broad category of 'disorders of initiating and maintaining sleep' (DIMS); however, the short sleeper phenotype or trait is not considered a sleep disorder. Individuals with this trait require less sleep in any 24-hour period than is typical for their age group.

See also familial advanced sleep-phase syndrome (FASPS; 604348), which is a distinct disorder characterized by very early sleep onset and offset.

Clinical Features

He et al. (2009) reported a mother and daughter with lifelong shorter daily sleep times than control individuals. The self-reported non-workday habitual sleep-offset times (awakening times) were much earlier than those of controls, although sleep-onset times (time of falling asleep) were similar to that of conventional sleepers. Per 24-hour day, the short sleepers slept an average of 6.25 hours compared with other family members who slept an average of 8.06 hours. Thus, the mother and daughter represented 'natural short sleepers.'

Molecular Genetics

In a mother and daughter with the short sleep phenotype, He et al. (2009) identified a heterozygous mutation in the DEC2 gene (P385R; 606200.0001).

Animal Model

He et al. (2009) found that heterozygous P385R-mutant DEC2 transgenic mice showed increased activity and less sleep time compared to wildtype mice. Under sleep deprivation, P385R-DEC2 transgenic mice also showed less compensatory gain in non-REM sleep compared to wildtype mice, suggesting a role for DEC2 in sleep homeostasis. There were no differences in circadian rhythm compared to wildtype mice. The phenotype was not found in Dec2-null mice, suggesting that expression of the P385R mutation leads to a dominant increase in the quantity of wakefulness. The phenotype was enhanced in the absence of endogenous Dec2, suggesting that P385R results in a dominant-negative mutation. Similar results were found for Drosophila carrying mouse Dec2-P385R compared to wildtype Dec2.