Metachromatic leukodystrophy due to saposin B deficiency is an inherited condition characterized by progressive loss of muscle tone/strength, motor abilities, and cognitive abilities. Its symptoms are similar to metachromatic leukodystrophy or MLD (please also see: metachromatic leukodystrophy), but has a different underlying genetic cause. This form is caused by a deficiency in the saposin B enzyme rather than arylsulfatase A enzyme. This form of metachromatic leukodystrophy also causes a harmful build up of sulfatides, a type of fat, in the cells. The symptoms of this condition most commonly onsets in late infancy where symptoms appear between one and two years of age. Later childhood and early adulthood onset has been reported in this form as well. Symptoms may include a regression (reversal) of motor development and mental development, such as an inability to walk or talk. There is currently no cure for metachromatic leukodystrophy due to saposin B deficiency.
This condition is inherited or passed through families in an autosomal recessive manner. This means that two copies of the changed gene are needed to produce the symptoms. In recessive conditions, each parent is an unaffected carrier of one genetic change. Each child born to two carriers has a 25% chance of being affected. A genetic counselor can be helpful in providing a better understanding of the inheritance and risks to future pregnancies. If you or someone you know has been diagnosed with metachromatic leukodystrophy due to saposin B deficiency, contact your doctor to discuss the most current treatment options.