What are FKTN-related Disorders?
FKTN-related Disorders includes a spectrum of conditions that cause muscle weakness because of a deficiency in the fukutin (FKTN) protein. Symptoms vary greatly from person to person, even among people in the same family. Some conditions can have a mild course, while others may have severe symptoms that can be fatal. The various conditions associated with mutations in the FKTN gene are described below in order of severity.
Walker-Warburg syndrome (WWS)
Walker-Warburg syndrome is the most severe presentation. Symptoms begin at birth and babies are born with severe abnormalities in the structure of the brain. Eye defects, such as cataracts at birth, unusually small eyes, or unusually large eyes, are common. Most patients only have control of their heads and do not develop the ability to move other body parts.
Fukuyama Congenital Muscular Dystrophy (FCMD)/Muscle-Eye-Brain Disease (MEB)
Fukuyama congenital muscular dystrophy and muscle-eye-brain disease have overlapping symptoms. Symptoms include muscle weakness and abnormalities in the structure of the brain that are less severe than in WWS. Less severe eye defects, such as glaucoma at birth, progressive nearsightedness, weakening of the retina, and cataracts in childhood, are common. Rarely, individuals with these conditions learn to walk at later stages in life and may speak a few words.
Limb Girdle Muscular Dystrophy type 2M (LGMD2M)
Limb Girdle Muscular Dystrophy type 2M is the most mild presentation. Age of onset and severity of symptoms vary greatly among individuals. Typically, the only symptom is weakness in the muscles closest to the body, specifically the muscles of the shoulders, upper arms, pelvic area, and thighs. Rarely, individuals have a heart condition called dilated cardiomyopathy. The brain and eyes are not affected.
How common are FKTN-related Disorders?
WWS is rare and the exact incidence is unknown, though it is more common in individuals of Ashkenazi Jewish descent. FCMD is rarely seen outside of individuals of Japanese descent where approximately 1 in 140,000 live births have the condition. All forms of LGMD affect 1 in 14,5000 to 1 in 123,000 live births and this specific type, LGMD2M, is rare with unknown specific incidence.
How are FKTN-related Disorders treated?
There is no successful treatment or cure for WWS or FCMD/MEB. Medical specialists can help treat specific symptoms, such as using medication to control seizures, placement of a shunt to reduce fluid buildup around the brain, tube feeding and physical and occupational therapy to aid in movement.
Treatment for LGMD2M mainly involves physical and occupational therapy, assistive devices, and monitoring for heart and breathing complications.
What is the prognosis for a person with a FKTN-related Disorder?
The prognosis depends on the severity of the condition. Individuals with WWS typically pass away in infancy. Individuals with FCMD/MEB typically live until childhood or in their teens. Those with LGMD2M do not typically have an altered lifespan.