McLeod neuroacanthocytosis syndrome

McLeod neuroacanthocytosis syndrome is a primarily neurological disorder that occurs almost exclusively in males. This disorder affects movement in many parts of the body. People with this condition also have abnormal star-shaped red blood cells (acanthocytosis). This condition is one of a group of disorders called neuroacanthocytoses that involve neurological problems and abnormal red blood cells.

The features of McLeod neuroacanthocytosis syndrome include muscle weakness (myopathy); muscle degeneration (atrophy); and involuntary jerking movements (chorea), particularly of the arms and legs. People with this disorder may also have reduced sensation and weakness in their arms and legs (peripheral neuropathy). Involuntary tensing of muscles (dystonia) in the face and throat can cause grimacing and vocal tics (such as grunting and clicking noises). Approximately half of all people with McLeod neuroacanthocytosis syndrome have seizures. Individuals with this condition may develop difficulty processing, learning, and remembering information (cognitive impairment). Heart problems such as irregular heartbeats (arrhythmia) and a weakened and enlarged heart (dilated cardiomyopathy) are also frequently seen in individuals with this disorder.

The signs and symptoms of McLeod neuroacanthocytosis syndrome usually begin in mid-adulthood. Behavioral changes, such as lack of self-restraint, the inability to take care of oneself, anxiety, depression, and changes in personality may be the first signs of this condition. While these behavioral changes are typically not progressive, the movement problems and intellectual impairments that are characteristic of this condition tend to worsen with age.

McLeod neuroacanthocytosis syndrome is rare; approximately 150 cases have been reported worldwide.

Mutations in the XK gene cause McLeod neuroacanthocytosis syndrome. The XK gene provides instructions for producing the XK protein, which carries the blood antigen Kx. Blood antigens are found on the surface of red blood cells and determine blood type. The XK protein is found in various tissues, particularly the brain, muscle, and heart. The function of the XK protein is unclear; researchers believe that it might play a role in transporting substances into and out of cells.

XK gene mutations typically lead to the production of an abnormally short, nonfunctional protein or cause no protein to be produced at all. A lack of XK protein leads to an absence of Kx antigens on red blood cells. This shortage of Kx antigen is known as the "McLeod phenotype," and refers only to the red blood cells. It is not known how the lack of XK protein leads to the movement problems and other features of McLeod neuroacanthocytosis syndrome.

Read more about the XK gene.

McLeod neuroacanthocytosis syndrome is inherited in an X-linked recessive pattern. The gene associated with this condition is located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation must be present in both copies of the gene to cause the disorder. Males are affected by X-linked recessive disorders much more frequently than females. Rarely, females with a mutation in one copy of the XK gene can have the characteristic misshapen blood cells and movement problems associated with McLeod neuroacanthocytosis syndrome. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.