In restless legs syndrome, the neural substrates of the sensorimotor symptoms are also normally involved in upright standing posture and biped walking

Summary 

Restless legs syndrome (RLS) exhibits sensorimotor symptoms. In familial cases, a gene at chromosomal location 9p-24-22 is linked to RLS and the expressed mutation is Dopamine Receptor Specific Individual Sensitivity (DRSIS).

The symptoms are triggered during changes in alertness, generally at sleep hours, resulting from insufficient dopamine transmission. The conscious experience of sensory abnormalities are described as ‘an urge to move the limbs with or without paresthesias’ leading to motor signs such as periodic limb movements and motor restlessness which exhibit temporary loss of extensor motor system dominance over the flexor motor system of the upright posture.

The relationship of the expressed mutation to EEG alpha activity makes RLS a sleep disorder as well as a cognitive dysfunction. The recurrent character of sensorimotor symptoms impede the patient’s ability to sleep, wake and force to move leading to insomnia.

In Üner Tan Syndrome, the nonsense mutation in the same gene leads to underdevelopment of the neural substrates of upright posture. The defects include dopamine receptor deficiency (DRD) leading to severe cognitive dysfunctions and motor disorders-complete loss of extensor motor system dominance over the flexor motor system-quadrupedality, primitive speech, cerebellar symptoms, and strabismus.

Comparisons between the neural substrates of sensorimotor symptoms seen in RLS and MRI findings for cases of Üner Tan Syndrome show cortico-cerebellar hypoplasias in the neural networks involved in upright posture.

Both RLS and Üner Tan Syndrome seem to be due to different mutations in the dopamine receptor gene at 9p-24 locus, affecting the diencephalon dopaminergic system and the neural networks involved in upright posture.