BioFarber – Biomarker for Farber Disease
Farber disease, also known as Farber’s lipogranulomatosis, is an autosomal recessive lysosomal storage disease marked by a deficiency in enzyme ceramidase which causes a progressive accumulation of fatty material lipids leading to abnormalities in the joints, liver, throat, tissues, and central nervous system.
Farber disease is an extremely rare disorder, with a prevalence of less than 1/1,000,000. Currently only about 80 cases have been reported worldwide. Disease onset is typically in early infancy but may also occur later in life.
It is inherited with an autosomal recessive pattern.
Background of information
The clinical presentation of Farber disease (FD) is characterized by the appearance of subcutaneous skin nodules, ordinarily near the joints, most often interphalangeal, wrist, elbow and ankle joints, or over points of mechanical pressure. These manifestations are very painful and lead to progressive joint stiffness, limitation of motion by contractures, and finally to immobilization and deformation of joints. Another characteristic sign of FD is the development of a progressive hoarseness due to laryngeal involvement.
In addition to these major manifestations, seven phenotypes have been described which differ in severity and additional organ involvement, such as the lungs, nervous system, heart, and lymph nodes. Dependent on residual lysosomal ceramidase turnover, patients have a variable degree of central nervous system disease, leading to progressive neurologic deterioration. In most cases the neuronal dysfunction rather than the general physical dystrophy seems to limit the duration of FD. As well, patients with FD may die due to pulmonary disease with interstitial pneumonia.
First symptoms usually appear between the newborn period and the first birthday. Milder forms of type 3 were described with onset at 20 months of age. Clinical manifestation in type 5 of FD, dominated by neurologic deterioration, begins at 1 to 2 1/2 years of life. Patients usually die within the first years of life, but prolonged courses in patients without severe CNS disease may also be observed.
Type 1 is the most common or classical, form of this condition and is associated with the classic signs of voice, skin, and joint problems that begin a few months after birth. Developmental delay and lung disease also commonly occur. Infants born with type 1 Farber lipogranulomatosis usually survive only into early childhood.
Types 2 and 3 generally have less severe signs and symptoms than the other types. Affected individuals have the three classic signs and usually do not have developmental delay. Children with these types of Farber lipogranulomatosis typically live into mid- to late childhood.
Types 4 and 5 are associated with severe neurological problems. Type 4 usually causes life-threatening health problems beginning in infancy due to massive lipid deposits in the liver, spleen, lungs, and immune system tissues. Children with this type typically do not survive past their first year of life. Type 5 is characterized by progressive decline in brain and spinal cord (central nervous system) function, which causes paralysis of the arms and legs (quadriplegia), seizures, loss of speech, involuntary muscle jerks (myoclonus), and developmental delay. Children with type 5 Farber lipogranulomatosis survive into early childhood.
Types 6 and 7 are very rare, and affected individuals have other associated disorders in addition to Farber lipogranulomatosis.
Farber lipogranulomatosis is caused by a mutation in the ASAH1 gene, situated on the short arm of
chromosome 8. This gene codes for acid ceramidase, a lysosomal heterodimeric enzyme that hydrolyzes ceramide into sphingosine and fatty acid. To date, less than 25 distinct mutations have been identified in Farber patients, but no large deletions have yet been reported. A total of 13 different mutations were identified including 1 splice, 1 polypyrimidine tract (PPT) deletion and 11 missense mutations. Eleven mutations were exclusive to the Indian population.
In Farber disease, the mutation in the ASAH1 gene leads to a reduction in acid ceramidase's activity of over 90%. Consequently the ceramide isn’t broken down properly and it gathers in the lysosomes of cell of various tissues, such as lung, liver, colon, skeletal muscles, cartilage, and bone. Certain studies on the inflammatory symptoms in FD indicates that the granulomatous inflammation is not a consequence of mere ceramide storage but reflects a dysregulation of leukocyte functions, probably due to the intracellular role of ceramide in intracellular signal transduction. However, the sequence of molecular mechanisms leading from a defect in ceramide metabolism to chronic granulomatous inflammation still needs elucidation. Alterations of receptor-mediated apoptosis by ceramide accumulation in inflammatory cells may be one of the mechanisms underlying abnormal granuloma formation.