XDP stands for X-linked dystonia-parkinsonism, a progressive neurodegenerative disease that causes involuntary muscle contractions (dystonia) followed by slow, rigid movement similar to Parkinson’s disease. It is sometimes called “Lubag” in the Philippines, where it originates almost exclusively among people with ancestry from the island of Panay. XDP is rare globally, affecting roughly 0.31 per 100,000 people in the Philippines, but in the province of Capiz on Panay, the rate climbs to about 1 in 4,000 men.
What Causes XDP
XDP traces to a specific genetic change in the TAF1 gene on the X chromosome. A parasitic piece of DNA called an SVA retrotransposon has inserted itself into one of the gene’s introns, disrupting how the gene is read and processed. This insertion causes abnormal splicing of the TAF1 gene, meaning cells produce less of the full-length protein they need. The reduction in TAF1 protein is especially damaging in the striatum, a brain region critical for coordinating movement.
All people with XDP share the same set of seven genetic variants clustered in and around the TAF1 gene, pointing to a single common ancestor. Of those seven variants, the SVA insertion is considered the primary driver of the disease. There is also evidence that a repeating six-letter DNA sequence within the SVA varies in length between patients, and longer repeats correlate with lower TAF1 levels. Over time, the loss of TAF1 leads to the death of medium spiny neurons in the striatum and abnormal iron buildup in the putamen, both hallmarks of the disease on brain imaging and autopsy.
How XDP Is Inherited
XDP follows an X-linked recessive inheritance pattern. Men have one X chromosome, so a single altered copy of TAF1 is enough to cause the disease. Women have two X chromosomes, so they typically need both copies to be affected, which is extremely rare. Women who carry one altered copy can pass it to their children but usually don’t develop symptoms themselves.
A small number of female carriers have developed movement problems linked to XDP. These tend to be milder than what men experience and generally don’t progress or cause disability. Fathers with XDP cannot pass the condition to their sons, since sons inherit their father’s Y chromosome, not his X.
Symptoms and How the Disease Progresses
The average age of onset is 39 in men, though it can appear anywhere from the early teens to the mid-60s. Women who develop symptoms tend to start later, around age 52. The disease typically begins with focal dystonia, involuntary sustained muscle contractions that affect one part of the body. Common early sites include the jaw, tongue, neck, or one limb. Over the following years, dystonia spreads to other body regions. The average time from the first symptom to generalized dystonia is about 3.8 years, though some people progress within a year and others take more than two decades.
As the disease advances, parkinsonian features emerge: slowness of movement, muscle rigidity, tremor, and difficulty with balance and walking. The combination can be devastating. People who develop both jaw and tongue dystonia along with neck dystonia early in the course tend to have the worst outcomes. They often become bedridden within a few years and face life-threatening complications like aspiration pneumonia (from difficulty swallowing), blocked airways from laryngeal spasm, and infections tied to immobility.
How XDP Is Diagnosed
Diagnosis rests on a combination of clinical features, family history, and ancestry from the Panay region of the Philippines. Genetic testing can confirm the presence of the SVA insertion and the associated variants in the TAF1 gene. Brain imaging can support the diagnosis by showing shrinkage of the striatum and iron deposits in the putamen, though these findings become more prominent as the disease progresses. Because XDP is so geographically concentrated, clinicians outside the Philippines may not immediately recognize it, making genetic testing especially important for Filipino patients presenting with dystonia or parkinsonism of unclear cause.
Treatment Options
There is no cure for XDP, and treatment focuses on managing symptoms. Most patients are tried on the same medications used for generalized dystonia: anticholinergic drugs that reduce involuntary muscle activity, muscle relaxants like baclofen, sedating medications such as clonazepam, and drugs that regulate dopamine signaling. Response varies widely, and no single medication reliably controls symptoms for all patients. Levodopa, the standard Parkinson’s treatment, has been studied in clinical trials for XDP’s parkinsonian symptoms, but results remain limited.
Deep brain stimulation (DBS), a surgical procedure that delivers electrical impulses to specific brain targets, has shown promise for the dystonia component of XDP. In reported cases where electrodes were placed in the globus pallidus internus, dystonia scores improved by roughly 68 to 81 percent at one-year follow-up. The response of parkinsonian symptoms to the same procedure is less consistent. Some patients saw dramatic improvement in both dystonia and parkinsonism, while others experienced significant dystonia relief but little to no change in rigidity, slowness, or gait problems. This uneven response means DBS can meaningfully improve quality of life for some patients but is not a complete solution.
Where the Disease Is Found
XDP is endemic to Panay Island in the central Philippines. The province of Capiz has the highest concentration, followed by Aklan, Iloilo, Antique, and Guimaras. Because of migration patterns, affected individuals and carriers now live in the United States, Canada, Germany, the United Kingdom, and Japan. As of 2010, more than 500 cases from 253 families had been recorded in the XDP Philippine Registry. The true number worldwide is likely higher, since cases outside the Philippines may go unrecognized or misdiagnosed as idiopathic dystonia or Parkinson’s disease.
Genetic Research and Potential Therapies
The clearest scientific lead centers on the SVA retrotransposon itself. Two independent studies have shown that removing the SVA insertion from cells using CRISPR gene-editing technology restores TAF1 protein levels to those seen in healthy cells. This is a laboratory finding, not yet a treatment available to patients, but it confirms that the SVA insertion is directly responsible for the reduced gene expression that drives neurodegeneration. Understanding the precise mechanism has opened the door to approaches that could one day correct or compensate for the genetic defect, whether through gene editing, therapies that boost TAF1 expression, or strategies that target the abnormal RNA splicing caused by the insertion.