SNP Shot: Genomic Insights

Action myoclonus–renal failure (AMRF) syndrome is characterized by involuntary muscle jerks or twitches, known as myoclonus, and frequently involves kidney (renal) disease. Despite the name, kidney problems are not present in all individuals with AMRF syndrome.

The movement difficulties associated with AMRF syndrome usually start with tremors, which are rhythmic shaking, primarily in the fingers and hands. These tremors are present at rest and are more pronounced during fine motor activities like writing. As the condition progresses, the tremors can spread to other areas of the body including the head, torso, legs, and tongue. Eventually, these tremors evolve into more forceful myoclonic jerks, often triggered by voluntary movement or the intention to move (action myoclonus). These jerks typically affect the torso, arms and legs, and face, particularly the muscles surrounding the mouth and eyelids. Myoclonus can be exacerbated by anxiety, excitement, stress, or extreme fatigue. Some individuals with AMRF syndrome may also experience seizures, peripheral neuropathy (nerve damage leading to loss of sensation and weakness in the limbs), or sensorineural hearing loss (hearing loss due to inner ear abnormalities). Severe seizures or myoclonus can be life-threatening.

If kidney problems develop in AMRF syndrome, a common early sign is proteinuria, or excess protein in the urine. Over time, kidney function declines, ultimately leading to end-stage renal disease, where the kidneys can no longer adequately filter waste and fluids.

The onset of AMRF syndrome typically occurs between the ages of 15 and 25, although it can present earlier or later in life. The age at which symptoms begin and the progression of the condition are variable, even within the same family. Either movement problems or kidney disease can be the initial symptom, or both may begin simultaneously. The typical survival time after the onset of symptoms is 7 to 15 years.

Inheritance:

AMRF syndrome follows an autosomal recessive inheritance pattern. This means that an individual must inherit a mutated copy of the responsible gene from both parents to develop the condition. The parents, who each carry only one copy of the mutated gene, are typically asymptomatic carriers.