People with Angelman syndrome take longer to fall asleep, have poorer sleep efficiency compared to normally developing individuals and tend to prefer “baby foods,” a review study says.
In their work, researchers propose that such behavioral biases may represent an extreme, abnormal manifestation of traits selected by evolution to promote social interaction between child and mother.
The study, “Baby food and bedtime: Evidence for opposite phenotypes from different genetic and epigenetic alterations in Prader-Willi and Angelman syndromes,” was published in the journal SAGE Open Medicine.
Normally a person inherits one copy of the UBE3A gene from each parent. Both copies of this gene are turned on (active) in many of the body’s tissues, but in certain brain areas, only the copy passed on by the mother is active. This type of parent-specific gene activation is known as genomic imprinting.
People with Angelman syndrome lose the expression of the maternal copy of UBE3A, which means they will not have active copies of this gene in some parts of the brain.
Prader-Willi syndrome is a related disorder, caused by other genetic defects but within the same chromosome 15 region affected in Angelman syndrome. But in contrast, people with Prader-Willi have lost or have an inactive paternal copy of that chromosomal region.
It has been argued that, given their genetic relationship, Angelman and Prader-Willi have opposing effects over the patient’s body. However, this remains a matter of debate.
To address this issue, researchers reviewed the existing evidence for opposite effects on sleep and eating behaviors on patients with Angelman syndrome versus Prader-Willi syndrome.
They conducted searches on published studies and reports looking at those behaviors in these patients. The results revealed that sleep structure and quality are altered in both syndromes.
Some studies show that patients with Angelman syndrome have increased sleep onset latency — they take more time to fall asleep as compared to typically developing individuals. They also sleep less and have less efficient sleep, which reflects in greater daytime sleepiness relative to healthy people.
There is evidence that those sleep disturbances are underpinned by a lower production of melatonin at nighttime. Melatonin is a hormone that regulates sleep-wake cycles. Normally, it is released by the brain during the night, peaking in the middle of the night and then falling to low levels by early morning.
In contrast, Prader-Willi patients tend to have a shorter sleep latency compared to normal individuals, even though they also have poorer sleep efficiency.
In terms of feeding behavior, the available evidence is more limited. It seems that those with Angelman and Prader-Willi syndromes share a tendency for overeating and food-seeking behaviors.
But patients with Angelman syndrome appear to have a preference for a narrower range of foods, especially those that resemble “baby foods” in texture, such as porridge, purees and other constant, soft and smooth textures.
Researchers believe the behavior of patients with Angelman syndrome may reflect an imbalance in manifestation of evolutionarily selected traits — specifically the demand for resources and attention from the mother.
“Paternally expressed genes may thus have been selected to favor an increased preference for complementary foods and prolonged parental care in juvenile stages,” researchers said. In people with Angelman syndrome, such behaviors would get to an extreme due to the lack of expression of the maternal gene copies.
The frequent smiling and laughter, typical symptoms of Angelman syndrome, are argued as signals of positive affection, which have benefits to the child, providing increased parental attention.
The need for more bedtime attention due to sleep problems and higher feeding requests associated with mother-provided “baby foods” also may have been selected to favor social interaction with the mother.
In light of the available studies done in mouse models and human patients, the authors also propose models to help explain how the different genetic alterations — on maternally and paternally expressed genes — could result in the observed behaviors associated with each of the syndromes.