Lowe syndrome is a condition that primarily affects the eyes, brain, and kidneys. This disorder occurs almost exclusively in males.

Infants with Lowe syndrome are born with thick clouding of the lenses in both eyes (congenital cataracts), often with other eye abnormalities that can impair vision. About half of affected infants develop an eye disease called infantile glaucoma, which is characterized by increased pressure within the eyes.

Many individuals with Lowe syndrome have delayed development, and intellectual ability ranges from normal to severely impaired. Behavioral problems and seizures have also been reported in children with this condition. Most affected children have weak muscle tone from birth (neonatal hypotonia), which can contribute to feeding difficulties, problems with breathing, and delayed development of motor skills such as sitting, standing, and walking.

Kidney (renal) abnormalities, most commonly a condition known as renal Fanconi syndrome, frequently develop in individuals with Lowe syndrome. The kidneys play an essential role in maintaining the right amounts of minerals, salts, water, and other substances in the body. In individuals with renal Fanconi syndrome, the kidneys are unable to reabsorb important nutrients into the bloodstream. Instead, the nutrients are excreted in the urine. These kidney problems lead to increased urination, dehydration, and abnormally acidic blood (metabolic acidosis). A loss of salts and nutrients may also impair growth and result in soft, bowed bones (hypophosphatemic rickets), especially in the legs. Progressive kidney problems in older children and adults with Lowe syndrome can lead to life-threatening renal failure and end-stage renal disease (ESRD).

Mutations in the OCRL gene cause Lowe syndrome. The OCRL gene provides instructions for making an enzyme that helps modify fat (lipid) molecules called membrane phospholipids. By controlling the levels of specific membrane phospholipids, the OCRL enzyme helps regulate the transport of certain substances to and from the cell membrane. This enzyme is also involved in the regulation of the actin cytoskeleton, which is a network of fibers that make up the cell's structural framework. The actin cytoskeleton has several critical functions, including determining cell shape and allowing cells to move.

Some mutations in the OCRL gene prevent the production of any OCRL enzyme. Other mutations reduce or eliminate the activity of the enzyme or prevent it from interacting with other proteins within the cell. Researchers are working to determine how OCRL mutations cause the characteristic features of Lowe syndrome. Because the OCRL enzyme is present throughout the body, it is unclear why the medical problems associated with this condition are mostly limited to the brain, kidneys, and eyes. It is possible that other enzymes may be able to compensate for the defective OCRL enzyme in unaffected tissues.

Normal Function

The OCRL gene provides instructions for making an enzyme that is present in cells throughout the body. This enzyme is part of a larger group of enzymes that modify fat (lipid) molecules known as membrane phospholipids. These molecules form the basic structure of cell membranes. Specifically, the OCRL enzyme regulates the levels of a membrane phospholipid called phosphatidylinositol 4,5-bisphosphate.

The OCRL enzyme is found in several areas within cells. It is concentrated in a complex network of membranes known as the trans-Golgi network, which sorts proteins and other molecules and sends them to their intended destinations inside or outside the cell. The OCRL enzyme is also found on endosomes, specialized compartments that are formed at the cell surface to carry proteins and other molecules to their destinations within the cell.

By controlling the level of phosphatidylinositol 4,5-bisphosphate, the OCRL enzyme helps regulate the transport of certain substances to and from the cell membrane and chemical signaling between cells. The enzyme may also be involved in the regulation of the actin cytoskeleton, which is a network of fibers that make up the cell's structural framework. The actin cytoskeleton has several critical functions, including determining cell shape and allowing cells to move.

Recent research suggests that the OCRL enzyme is found in cell structures called primary cilia, which are microscopic, finger-like projections that stick out from the surface of cells and are involved in signaling pathways that transmit information between cells. Cilia are important for the structure and function of many types of cells, including cells in the brain, kidneys, and liver. Cilia are also necessary for the perception of sensory input (such as sight, hearing, and smell). Studies suggest that the OCRL enzyme may play a role in the formation, function, and maintenance of cilia.

Health Conditions Related to Genetic Changes

Dent disease

At least 20 mutations in the OCRL gene have been found to cause Dent disease 2. This form of Dent disease is characterized by chronic kidney problems; some affected individuals also have mild intellectual disability, weak muscle tone (hypotonia), and clouding of the lens of the eyes (cataract) that does not impair vision. Some researchers consider Dent disease 2 to be a mild variant of Lowe syndrome, which is discussed below.

The OCRL gene mutations that cause Dent disease 2 reduce or eliminate the function of the OCRL enzyme. These changes impair the transport of certain molecules and regulation of the actin cytoskeleton. They may also affect cell signaling by altering the structure or function of cilia. Disruption of these important cell activities likely impairs kidney function, leading to excess protein in the urine (proteinuria), kidney stones, and ultimately kidney failure. It is unknown how loss of the OCRL enzyme contributes to the other signs and symptoms of this condition.

Because the OCRL enzyme is present throughout the body, it is unclear why Dent disease 2 primarily affects the kidneys and, to a lesser extent, the brain, eyes, and other tissues. It is possible that other enzymes may be able to compensate for the defective OCRL enzyme in unaffected tissues.

Lowe syndrome

More than 120 mutations in the OCRL gene have been identified in individuals with Lowe syndrome, a condition that affects the eyes, brain, and kidneys. Some of these mutations prevent the production of any OCRL enzyme. Other mutations reduce or eliminate the activity of the enzyme or prevent it from interacting with other proteins within the cell. Researchers believe that the effects of these genetic changes are similar to those of the mutations that cause Dent disease 2: the mutations likely alter the transport of molecules within cells, regulation of the actin cytoskeleton, and the structure and function of cilia. It is unknown why some OCRL gene mutations cause Lowe syndrome and others cause Dent disease 2.

Because the OCRL enzyme is present throughout the body, it is unclear why Lowe syndrome primarily affects the kidney, brain, and eyes. As with Dent disease 2, it is possible that other enzymes may be able to compensate for the defective OCRL enzyme in unaffected tissues.

Other Names for This Gene

• INPP5F
• LOCR
• Lowe oculocerebrorenal syndrome protein
• NPHL2
• OCRL1
• OCRL_HUMAN
• oculocerebrorenal syndrome of Lowe
• phosphatidylinositol polyphosphate 5-phosphatase

Genomic Location

This condition is inherited in an X-linked pattern. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, 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. Most X-linked disorders affect males much more frequently than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

In some cases of Lowe syndrome, an affected male inherits the mutation from a mother who carries one altered copy of the OCRL gene. Other cases result from new mutations in the gene and occur in males with no history of the disorder in their family.

Females who carry one mutated copy of the OCRL gene do not have the characteristic features of Lowe syndrome. Most female carriers, however, have changes in the lens of the eye that can be observed with a thorough eye examination. These changes typically do not impair vision.

Lowe syndrome is an uncommon condition. It has an estimated prevalence of 1 in 500,000 people.