Farber lipogranulomatosis

Farber lipogranulomatosis is a rare inherited condition involving the breakdown and use of fats in the body (lipid metabolism). In affected individuals, harmful amounts of lipids accumulate in cells and tissues throughout the body, particularly around the joints.

Three classic signs are seen with Farber lipogranulomatosis: a hoarse voice or a weak cry, small lumps of fat under the skin and in other tissues (lipogranulomas), and swollen and painful joints. Other problems that can occur include difficulty breathing, an enlarged liver and spleen (hepatosplenomegaly), and intellectual disability.

Researchers have described seven types of Farber lipogranulomatosis based on their characteristic features.

Type 1 is the most common form of this condition and is associated with the classic signs of voice, skin, and joint problems. Frequently, intellectual disability and lung disease have also been reported. Infants born with this form of the disorder usually survive only into early childhood.

Types 2 and 3 generally have milder signs and symptoms than the other types. Affected individuals have the three classic signs with mild, if any, intellectual disability and they generally live longer than those with type 1.

Types 4 and 5 are associated with severe intellectual disability. Type 4 usually causes life-threatening medical problems beginning in infancy due to massive fat deposits in the liver, spleen, lymph nodes, lungs, and thymus (a gland located behind the breastbone that plays an important role in immune system function). Type 5 is characterized by progressive central nervous system decline, which causes paralysis of the arms and legs (quadriplegia), seizures, loss of speech, irregular involuntary muscle contraction (myoclonus), and intellectual disability.

Types 6 and 7 have been seen in only one person each and involve other disorders in addition to Farber lipogranulomatosis.

Farber lipogranulomatosis is a very rare disorder. About 80 individuals affected by this condition have been reported worldwide.

Mutations in the ASAH1 gene cause Farber lipogranulomatosis.

The ASAH1 gene provides instructions for making an enzyme called acid ceramidase. This enzyme is found in the lysosomes (compartments that digest and recycle materials in the cell), where it breaks down fats called ceramides so that these fats can be used by the body. Ceramides make up one subtype of a group of fats called sphingolipids.

The ceramide accumulation in Farber lipogranulomatosis results from an inability to break down ceramides in the lysosomes. Mutations in the ASAH1 gene lead to a shortage of functional acid ceramidase, which prevents lysosomes from breaking down ceramides properly. Without the activity of acid ceramidase, ceramides can build up in the lysosomes of cells and tissues in the lung, liver, colon, muscles used for movement (skeletal muscles), cartilage, and bone. This buildup causes the signs and symptoms of Farber lipogranulomatosis, and the severity of the disease depends on the amount of ceramide accumulation.

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.