Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a neurological condition characterized by changes to certain areas of the brain. A hallmark of ALSP is leukoencephalopathy, which is the alteration of a type of brain tissue called white matter. White matter consists of nerve fibers (axons) covered by a substance called myelin that insulates and protects them. The axons extend from nerve cells (neurons) and transmit nerve impulses throughout the body. Areas of damage to this brain tissue (white matter lesions) can be seen with magnetic resonance imaging (MRI). Another feature of ALSP is swellings called spheroids in the axons of the brain, which are a sign of axon damage. Also common in ALSP are abnormally pigmented glial cells. Glial cells are specialized brain cells that protect and maintain neurons. Damage to myelin and neurons is thought to contribute to many of the neurological signs and symptoms in people with ALSP.

Symptoms of ALSP usually begin in a person's forties and worsen over time. Personality changes, including depression and a loss of social inhibitions, are among the earliest symptoms of ALSP. Affected individuals may develop memory loss and loss of executive function, which is the ability to plan and implement actions and develop problem-solving strategies. Loss of this function impairs skills such as impulse control, self-monitoring, and focusing attention appropriately. Some people with ALSP have mild seizures, usually only when the condition begins. As ALSP progresses, it causes a severe decline in thinking and reasoning abilities (dementia).

Over time, motor skills are affected, and people with ALSP may have difficulty walking. Many develop a pattern of movement abnormalities known as parkinsonism, which includes unusually slow movement (bradykinesia), involuntary trembling (tremor), and muscle stiffness (rigidity). The pattern of cognitive and motor problems are variable, even among individuals in the same family, although almost all affected individuals ultimately become unable to walk, speak, and care for themselves.

ALSP was previously thought to be two separate conditions, hereditary diffuse leukoencephalopathy with spheroids (HDLS) and familial pigmentary orthochromatic leukodystrophy (POLD), both of which cause very similar white matter damage and cognitive and movement problems. POLD was thought to be distinguished by the presence of pigmented glial cells and an absence of spheroids; however, people with HDLS can have pigmented cells, too, and people with POLD can have spheroids. HDLS and POLD are now considered to be part of the same disease spectrum, which researchers have recommended calling ALSP.

Normal Function

The CSF1R gene provides instructions for making a protein called the colony stimulating factor 1 receptor (CSF-1 receptor). This protein is found in the outer membrane of certain cell types. When a specific protein called colony stimulating factor 1 attaches (binds) to it, the receptor turns on (activates) a series of proteins inside the cell that are part of multiple signaling pathways. The signaling pathways stimulated by the CSF-1 receptor control many important cellular processes such as cell growth and division (proliferation) and maturation of cells to take on specific functions (differentiation).

In the brain, the CSF-1 receptor is abundant in the membrane of specialized cells called glial cells. These cells protect and maintain nerve cells (neurons). The CSF-1 receptor is thought to be involved in the proliferation and differentiation of glial cells, but its exact role in the brain is unclear.

Health Conditions Related to Genetic Changes

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia

More than a dozen mutations in the CSF1R gene have been found in people with adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP). ALSP is a severe neurological disorder characterized by damage to a type of brain tissue called white matter. Symptoms of this condition typically begin in adulthood and progress to severe cognitive and movement problems. Most CSF1R gene mutations in ALSP change single protein building blocks (amino acids) in the CSF-1 receptor. Other mutations change the sequence of amino acids in other ways. The mutations all occur in the region of the receptor that activates other proteins (called the kinase domain). It is likely that the altered receptor is unable to stimulate cell signaling pathways. However, it is unclear how the gene mutations lead to white matter damage or cognitive and movement problems in people with ALSP.

Other Names for This Gene

• C-FMS
• CD115
• CD115 antigen
• CSF-1 receptor
• CSF-1R
• CSF1R_HUMAN
• CSFR
• FIM2
• FMS
• FMS proto-oncogene
• M-CSF-R
• macrophage colony stimulating factor I receptor
• macrophage colony-stimulating factor 1 receptor
• McDonough feline sarcoma viral (v-fms) oncogene homolog
• proto-oncogene c-Fms

Genomic Location