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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). Autosomal recessive inheritance (Orphanet)

Gene (location): Gene(s) directly associated with this condition or phenotype.	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 description

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

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).

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Growth delay

MedGen UID:: 99124
•Concept ID:: C0456070
•: Pathologic Function

A deficiency or slowing down of growth pre- and postnatally.

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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.

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Hepatomegaly

MedGen UID:: 42428
•Concept ID:: C0019209
•: Finding

Abnormally increased size of the liver.

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Increased hepatic glycogen content

MedGen UID:: 344698
•Concept ID:: C1856285
•: Finding

An increase in the amount of glycogen stored in hepatocytes compared to normal.

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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.

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Muscle weakness

MedGen UID:: 57735
•Concept ID:: C0151786
•: Finding

Reduced strength of muscles.

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Splenomegaly

MedGen UID:: 52469
•Concept ID:: C0038002
•: Finding

Abnormal increased size of the spleen.

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Hypoglycemia

MedGen UID:: 6979
•Concept ID:: C0020615
•: Disease or Syndrome

A decreased concentration of glucose in the blood.

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Hyperuricemia

MedGen UID:: 149260
•Concept ID:: C0740394
•: Disease or Syndrome

An abnormally high level of uric acid in the blood.

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Increased muscle glycogen content

MedGen UID:: 409660
•Concept ID:: C1968729
•: Finding

An increased amount of glycogen in muscle tissue.

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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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