Glycogen storage disease VIII is one of a group of hereditary disorders caused by a lack of one or more enzymes involved in glycogen synthesis or breakdown and characterized by deposition of abnormal amounts or types of glycogen in tissues. Excessive amounts of glycogen (which acts to store energy for later use) are deposited in the liver, causing it to become enlarged (hepatomegaly).

The three main features of phosphoglycerate kinase deficiency are hemolytic anemia, intellectual disability, and muscle problems (myopathy). An individual with the disorder may be affected by one or more of these features, but it is unusual for one person to exhibit all three signs.

Individuals with childhood PGK deficiency have some degree of Intellectual disability with delayed language acquisition. Some have epilepsy and strokes.

Most adult patients are moderately affected, and heterozygous females may show only mild hemolytic anemia with no myopathy or intellectual disability.

Myopathy with exercise-induced stiffness, cramps, and muscle Pain is seen in adolescents and young adult males. The cramps are often severe and may incapacitate the individual for hours. Myoglobinuria is often seen in severe episodes.

PGK is considered to be an inborn error of metabolism that is inherited in an X-linked manner. The gene responsible is located on the X chromosome (Xq13).

Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome Xq13” refers to band 13 on the long arm of the X chromosome. The numbered bands specify the location of the thousands of genes that are present on each chromosome.

X-linked genetic disorders are conditions caused by an abnormal gene on the X chromosome and manifest mostly in males.  Females that have a defective gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display symptoms because females have two X chromosomes and only one carries the defective gene.  Males have one X chromosome that is inherited from their mother and if a male inherits an X chromosome that contains a defective gene he will develop the disease.

Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease and a 25% chance to have an unaffected son.

If a male with an X-linked disorder is able to reproduce, he will pass the defective gene to all of his daughters who will be carriers.  A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male offspring.

Treatment of phosphoglycerate kinase deficiency may consist of iron supplements and blood transfusions when needed. The avoidance of strenuous exercise when evidence that muscle breakdown has taken place is very important and special care is needed during neurologic crisis to avoid life-threatening situations. Bone marrow transplantation may be an option in cases with severe neurological deterioration.

Genetic counseling may be of benefit for patients and their families. Other treatment is symptomatic and supportive.

Phosphoglycerate kinase deficiency is a very rare disorder that is fully expressed in males only. However, females who carry a single copy of the disease gene (heterozygous carriers) may exhibit some symptoms associated with the disorder (i.e., hemolytic anemia). The disorder can be diagnosed at birth when enzymatic testing is done. More than 30 cases of PGK deficiency have been written up in the medical literature. It is thought that there are people with the disease who do not receive a diagnosis.

Iron supplements and blood transfusions may help