In these cases, although the twins did form from the same fertilized egg, it is incorrect to refer to them as genetically identical, since they have different karyotypes. Semi-identical (sesquizygotic) twins
Monozygotic twins can develop differently, due to their genes being differently activated. More unusual are "semi-identical twins", also known as "sesquizygotic". As of 2019, only two cases have been reported. These "half-identical twins" are hypothesized to occur when an unfertilized egg cleaves into two identical attached ova, both of which are viable for fertilization. Both ova are then fertilized, each by a different sperm, and the coalesced zygotes undergo further cell duplications developing as a chimeric blastomere. If this blastomere then undergoes a twinning event, two embryos will be formed, with different paternal genetic information and identical maternal genetic information. This results in a set of twins with identical gene sequence from the mothers side, but different sequences from the fathers side. Cells in each fetus carry chromosomes from either sperm, resulting in chimeras. This form had been speculated until only recently being recorded. In 2007, a study reported a case of a pair of living twins, which shared an identical set of maternal chromosomes, while each having a distinct set of paternal chromosomes, albeit from the same man, and thus they most likely share half of their fathers genetic makeup. The twins were both found to be chimeras. One was an intersex XX, and one a XY male.
A comprehensive evaluation of the human metabolome in sleep deprivation in 2014 found that 27 metabolites are increased after 24 waking hours and suggested serotonin, tryptophan, and taurine may contribute to the antidepressive effect.The incidence of relapse can be decreased by combining sleep deprivation with medication or a combination of light therapy and phase advance (going to bed substantially earlier than ones normal time). Many tricyclic antidepressants suppress REM sleep, providing an additional evidence for a link between mood and sleep. Similarly, tranylcypromine has been shown to completely suppress REM sleep at adequate doses. Treating insomnia
Sleep deprivation can be implemented for a short period of time in the treatment of insomnia. Some common sleep disorders have been shown to respond to cognitive behavioral therapy for insomnia. Cognitive behavioral therapy for insomnia is a multicomponent process that is composed of stimulus control therapy, sleep restriction therapy (SRT), and sleep hygiene therapy. One of the components is a controlled regime of "sleep restriction" in order to restore the homeostatic drive to sleep and encourage normal "sleep efficiency". Stimulus control therapy is intended to limit behaviors intended to condition the body to sleep while in bed. The main goal of stimulus control and sleep restriction therapy is to create an association between bed and sleep. Although sleep restriction therapy shows efficacy when applied as an element of cognitive-behavioral therapy, its efficacy is yet to be proven when used alone. Sleep Hygiene therapy is intended to help patients develop and maintain good sleeping habits.