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What Is AP-4 HSP?
AP-4 Hereditary Spastic Paraplegia, also know as AP-4 Deficiency Syndrome, includes four sub-types of Hereditary Spastic Paraplegia: SPG47, SPG50, SPG51 and SPG52. Each of these HSP sub-types is associated with a defective autosomal recessive gene which causes a failure in the AP-4 Adaptor Complex. The phenotype and prognosis for each of the four sub-types is extremely similar. Patients afflicted with any of the AP-4 HSP genetic disorders generally present with symptoms including global developmental delay, microcephaly, seizures, malformation of the brain, and hypotonia (low-muscle tone). The few patients that learn to walk independently tend to lose that ability a few months or a few years later as they develop hypertonia (high-muscle tone) and muscle spasticity. Of the ~150 confirmed cases of AP-4 HSP in the world at this time, most patients have progressed to loss of mobility in some or all extremities, and are severely intellectually challenged. Because of the extreme rarity of AP-4 HSP, very little research has been conducted to date, and there is no known treatment or cure at this time.
SPG47, SPG50, SPG51 and SPG52 are caused by mutations in the AP4B1, AP4M1, AP4E1 and AP4S1 genes respectively. Each is an autosomal recessive disorder, which means that both parents have contributed a defective recessive gene to the child. The result is that the patient is unable to correctly produce a protein required for proper functioning of the AP-4 Adaptor Complex. The area of highest expression is central motor neurons located in the hippocampus region of the brain. It is also now known that AP-4 malfunction causes a deficiency with an autophagy compound called ATG9A.
The Cure AP-4 non-profit organization was founded in 2016 by families of two of the known SPG47 patients. It was originally founded as Cure SPG47, but the mission has since expanded to include all four AP-4 related disorders due to shared natural history, goals and patient/family needs. We refuse to accept the bleak prognosis which our children face. We have decided to fight. The purpose of this organization is to study and seek a cure for all AP-4 HSP disorders. We aim to improve the quality of life for children impacted by AP-4 HSP by accelerating the research for cures and treatments and providing support for patient therapies critical to their well-being and rehabilitation.