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Glycogen storage disease IXb(GSD9B)

MedGen UID:
107772
Concept ID:
C0543514
Disease or Syndrome
Synonyms: GLYCOGENOSIS OF LIVER AND MUSCLE, AUTOSOMAL RECESSIVE; GSD IXb; GSD9B; PHKB-Related Phosphorylase Kinase Deficiency; PHOSPHORYLASE KINASE DEFICIENCY OF LIVER AND MUSCLE, AUTOSOMAL RECESSIVE
SNOMED CT: Glycogen storage disease due to liver and muscle glycogen phosphorylase kinase deficiency (860860004); Glycogen storage disease type IXB (860860004)
Modes of inheritance:
Autosomal recessive inheritance
MedGen UID:
141025
Concept ID:
C0441748
Intellectual Product
Source: Orphanet
A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in individuals with two pathogenic alleles, either homozygotes (two copies of the same mutant allele) or compound heterozygotes (whereby each copy of a gene has a distinct mutant allele).
 
Gene (location): PHKB (16q12.1)
 
Monarch Initiative: MONDO:0009868
OMIM®: 261750
Orphanet: ORPHA79240

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 IXb (GSD9B), in which phosphorylase kinase is deficient in both liver and muscle, is characterized by predominantly mild symptoms including hepatomegaly, hypoglycaemia only after prolonged fasting, and in some cases muscle hypotonia (summary by Beauchamp et al., 2007). For a discussion of genetic heterogeneity of GSD IX, see GSD9A (306000).  http://www.omim.org/entry/261750
From MedlinePlus Genetics
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.

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.

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).

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.  https://medlineplus.gov/genetics/condition/glycogen-storage-disease-type-ix

Clinical features

From HPO
Short stature
MedGen UID:
87607
Concept ID:
C0349588
Finding
A height below that which is expected according to age and gender norms. Although there is no universally accepted definition of short stature, many refer to "short stature" as height more than 2 standard deviations below the mean for age and gender (or below the 3rd percentile for age and gender dependent norms).
Growth delay
MedGen UID:
99124
Concept ID:
C0456070
Pathologic Function
A deficiency or slowing down of growth pre- and postnatally.
Diarrhea
MedGen UID:
8360
Concept ID:
C0011991
Sign or Symptom
Abnormally increased frequency (usually defined as three or more) loose or watery bowel movements a day.
Hepatomegaly
MedGen UID:
42428
Concept ID:
C0019209
Finding
Abnormally increased size of the liver.
Increased hepatic glycogen content
MedGen UID:
344698
Concept ID:
C1856285
Finding
An increase in the amount of glycogen stored in hepatocytes compared to normal.
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.
Muscle weakness
MedGen UID:
57735
Concept ID:
C0151786
Finding
Reduced strength of muscles.
Splenomegaly
MedGen UID:
52469
Concept ID:
C0038002
Finding
Abnormal increased size of the spleen.
Hypoglycemia
MedGen UID:
6979
Concept ID:
C0020615
Disease or Syndrome
A decreased concentration of glucose in the blood.
Hyperuricemia
MedGen UID:
149260
Concept ID:
C0740394
Disease or Syndrome
An abnormally high level of uric acid in the blood.
Increased muscle glycogen content
MedGen UID:
409660
Concept ID:
C1968729
Finding
An increased amount of glycogen in muscle tissue.
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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