- Diarrhea (HP:0002014): Abnormally increased frequency (usually defined as three or more) loose or watery bowel movements a day. Evidence: TAS. (OMIM:261750)
- Short stature (HP:0004322): 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). Evidence: PCS. Frequency: 3/15. (PMID:17689125)
- Reduced hepatic phosphorylase kinase activity (HP:6000333): 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. Evidence: PCS. (PMID:21634085)
- Hypotonia (HP:0001252): 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. Evidence: PCS. Frequency: 2/15. (PMID:17689125)
- Hepatomegaly (HP:0002240): Abnormally increased size of the liver. Evidence: PCS. Frequency: 10/15. (PMID:17689125)
- Infantile onset (HP:0003593): Onset of signs or symptoms of disease between 28 days to one year of life. Evidence: PCS. (PMID:17689125)
- Reduced tissue phosphorylase kinase activity (HP:6000832): Concentration or activity of phosphorylase kinase below the lower limit of normal. This enzyme can be measured in multiple tissues including leukocytes and cultured fibroblasts. Evidence: TAS. (OMIM:261750)
- Increased muscle glycogen content (HP:0009051): An increased amount of glycogen in muscle tissue. Evidence: TAS. (OMIM:261750)
- Childhood onset (HP:0011463): Onset of disease at the age of between 1 and 5 years. Evidence: PCS. (PMID:17689125)
- Autosomal recessive inheritance (HP:0000007): 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). Evidence: PCS. (PMID:9215682)
- Hypoglycemia (HP:0001943): A decreased concentration of glucose in the blood. Evidence: PCS. Frequency: 10/15. (PMID:17689125)
- Muscle weakness (HP:0001324): Reduced strength of muscles. Evidence: TAS. Frequency: 3/15. (OMIM:261750)
- Growth delay (HP:0001510): A deficiency or slowing down of growth pre- and postnatally. Evidence: PCS. Frequency: 7/15. (PMID:17689125)
- Increased hepatic glycogen content (HP:0006568): An increase in the amount of glycogen stored in hepatocytes compared to normal. Evidence: TAS. (OMIM:261750)
- Splenomegaly (HP:0001744): Abnormal increased size of the spleen. Evidence: PCS. Frequency: 2/15. (PMID:17689125)
- Hyperuricemia (HP:0002149): The concentration of uric acid in the blood circulation is above the upper limit of normal. Evidence: PCS. Frequency: 1/5. (PMID:17689125)
These phenotypes are associated with the disease glycogen storage disease IXb (OMIM:261750).