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Glycogen storage disease IXa1(GSD8, FORMERLY; XLG1; GSD9A1)

MedGen UID:
854172
Concept ID:
C3694531
Disease or Syndrome
Synonyms: Glycogen storage disease 8; Glycogenosis type 8; GSD VIII; Hepatic phosphorylase kinase deficiency; LIVER GLYCOGENOSIS, X-LINKED, TYPE I; PHKA2-Related Phosphorylase Kinase Deficiency; Phosphorylase kinase deficiency of liver; X-linked Liver Glycogenosis Type 1; X-linked Liver Glycogenosis Type 2
 
Gene (location): PHKA2 (Xp22.13)
 
Monarch Initiative: MONDO:0010598
OMIM®: 306000

Disease characteristics

Excerpted from the GeneReview: Phosphorylase Kinase Deficiency
Phosphorylase kinase (PhK) deficiency causing glycogen storage disease type IX (GSD IX) results from deficiency of the enzyme phosphorylase b kinase, which has a major regulatory role in the breakdown of glycogen. The two types of PhK deficiency are liver PhK deficiency (characterized by early childhood onset of hepatomegaly and growth restriction, and often, but not always, fasting ketosis and hypoglycemia) and muscle PhK deficiency, which is considerably rarer (characterized by any of the following: exercise intolerance, myalgia, muscle cramps, myoglobinuria, and progressive muscle weakness). While symptoms and biochemical abnormalities of liver PhK deficiency were thought to improve with age, it is becoming evident that affected individuals need to be monitored for long-term complications such as liver fibrosis and cirrhosis. [from GeneReviews]
Authors:
Mrudu Herbert  |  Jennifer L Goldstein  |  Catherine Rehder, et. al.   view full author information

Additional descriptions

From OMIM
Glycogen storage disease type IX is a metabolic disorder resulting from a deficiency of hepatic phosphorylase kinase, a hexadecameric enzyme comprising 4 copies each of 4 unique subunits encoded by 4 different genes: alpha (PHKA2), beta (PHKB; 172490), gamma (PHKG2; 172471), and delta (CALM1; 114180). Mutations within the PHKA2, PHKB, and PHKG2 genes result in GSD9A, GSD9B (261750), and GSD9C (613027), respectively. GSD IXa is an X-linked recessive disorder, whereas the others are autosomal recessive. GSD IXa has been further divided into types IXa1 (GSD9A1), with no PHK activity in liver or erythrocytes, and IXa2 (GSD9A2), with no PHK in liver, but normal activity in erythrocytes. The clinical presentation of both subtypes is the same, and both are caused by mutations in the PHKA2 gene. However, mutations that result in IXa2 are either missense or small in-frame deletions or insertions enabling residual enzyme expression in erythrocytes (Keating et al., 1985; Hendrickx et al., 1994; Beauchamp et al., 2007). See also X-linked muscle PHK deficiency (GSD9D; 300559), caused by mutation in the gene encoding the muscle-specific alpha PHK subunit (PHKA1; 311870).  http://www.omim.org/entry/306000
From MedlinePlus Genetics
In a small number of people with GSD IX, the liver and muscles are both affected. These individuals develop a combination of the features described above, although the muscle problems are usually mild.

GSD IX can affect muscle tissue, although this form of the condition is very rare and not well understood. The features of this form of the condition can appear anytime from childhood to adulthood. Affected individuals may experience fatigue, muscle pain, and cramps, especially during exercise (exercise intolerance). Most affected individuals have muscle weakness that worsens over time. GSD IX can cause myoglobinuria, which occurs when muscle tissue breaks down abnormally and releases a protein called myoglobin that is excreted in the urine. Myoglobinuria can cause the urine to be red or brown.

When GSD IX affects the liver, the signs and symptoms typically begin in early childhood. The initial features are usually an enlarged liver (hepatomegaly) and slow growth. Affected children are often shorter than normal. During prolonged periods without food (fasting), affected individuals may have low blood sugar (hypoglycemia) or elevated levels of ketones in the blood (ketosis). Ketones are molecules produced during the breakdown of fats, which occurs when stored sugars are unavailable. Affected children may have delayed development of motor skills, such as sitting, standing, or walking, and some have mild muscle weakness. Puberty is delayed in some adolescents with GSD IX. In the form of the condition that affects the liver, the signs and symptoms usually improve with age. Typically, individuals catch up developmentally, and adults reach normal height. However, some affected individuals have a buildup of scar tissue (fibrosis) in the liver, which can rarely progress to irreversible liver disease (cirrhosis).

Glycogen storage disease type IX (also known as GSD IX) is a condition caused by the inability to break down a complex sugar called glycogen. The different forms of the condition can affect glycogen breakdown in liver cells or muscle cells or sometimes both. A lack of glycogen breakdown interferes with the normal function of the affected tissue.  https://medlineplus.gov/genetics/condition/glycogen-storage-disease-type-ix

Clinical features

From HPO
Fatigue
MedGen UID:
41971
Concept ID:
C0015672
Sign or Symptom
A subjective feeling of tiredness characterized by a lack of energy and motivation.
Growth delay
MedGen UID:
99124
Concept ID:
C0456070
Pathologic Function
A deficiency or slowing down of growth pre- and postnatally.
Hepatomegaly
MedGen UID:
42428
Concept ID:
C0019209
Finding
Abnormally increased size of the liver.
Motor delay
MedGen UID:
381392
Concept ID:
C1854301
Finding
A type of Developmental delay characterized by a delay in acquiring motor skills.
Hypotonia
MedGen UID:
10133
Concept ID:
C0026827
Finding
Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.
Splenomegaly
MedGen UID:
52469
Concept ID:
C0038002
Finding
Abnormal increased size of the spleen.
Lactic acidosis
MedGen UID:
1717
Concept ID:
C0001125
Disease or Syndrome
An abnormal buildup of lactic acid in the body, leading to acidification of the blood and other bodily fluids.
Hypercholesterolemia
MedGen UID:
5687
Concept ID:
C0020443
Disease or Syndrome
An increased concentration of cholesterol in the blood.
Hypoglycemia
MedGen UID:
6979
Concept ID:
C0020615
Disease or Syndrome
A decreased concentration of glucose in the blood.
Ketosis
MedGen UID:
7206
Concept ID:
C0022638
Disease or Syndrome
Presence of elevated levels of ketone bodies in the body.
Hyperuricemia
MedGen UID:
149260
Concept ID:
C0740394
Disease or Syndrome
An abnormally high level of uric acid in the blood.
Hypertriglyceridemia
MedGen UID:
167238
Concept ID:
C0813230
Finding
An abnormal increase in the level of triglycerides in the blood.
Elevated circulating hepatic transaminase concentration
MedGen UID:
338525
Concept ID:
C1848701
Finding
Elevations of the levels of SGOT and SGPT in the serum. SGOT (serum glutamic oxaloacetic transaminase) and SGPT (serum glutamic pyruvic transaminase) are transaminases primarily found in the liver and heart and are released into the bloodstream as the result of liver or heart damage. SGOT and SGPT are used clinically mainly as markers of liver damage.
Reduced hepatic phosphorylase kinase activity
MedGen UID:
1054423
Concept ID:
CN377142
Finding
Activity of phosphorylase kinase in liver tissue below the lower limit of normal. Phosphorylase kinase (PhK) has a major regulatory role in the breakdown of glycogen. The enzyme PhK comprises four copies each of four subunits, encoded by PHKA1, PHKA2, PHKB, and PHKG.

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