Likely inborn error of metabolism

Gene: ATP6AP2

Green List (high evidence)

Comment on list classification: There are 3 unrelated families reported in literature where individuals harboured hemizygous ATP6AP2 missense variants, and presented with a congenital disorder of glycosylation (primarily manifesting by liver disease and immunodeficiency). Patients with hemizygous nonsense variants present with a different phenotype (DEE-type neurological presentation), though glycosylation abnormalities were also seen in patient fibroblasts. Hence, this gene should be promoted to Green on Congenital disorders of glycosylation.

Created: 8 Jul 2026, 12:15 p.m. | Last Modified: 8 Jul 2026, 12:28 p.m.

Panel Version: 8.6

PMID: 41131679 Raynor et al., 2026
Authors identified three males and one female from three families with ATP6AP2 splicing variants (confirmed splicing effects by RNA-seq) and ID/DD, severe epilepsy (3 male patients), axial hypotonia, axonal neuropathy and microcephaly; the heterozygous female has a milder phenotype (at 14yrs she had mild ID, autism, and progressive microcephaly). RNA-Seq in patient-derived fibroblasts validated defective splicing, correlated with lowered ATP6AP2 protein levels in fibroblasts alongside glycosylation abnormalities. No liver involvement in these 4 patients.

PMID: 38075676 Fang et al., 2023
11mo Chinese male patient with a novel hemizygous ATP6AP2 variant c.185G>A (p.Gly62Glu) and a congenital disorder of glycosylation. He presented with recurrent jaundice, cutis laxa, cirrhosis, growth retardation, coagulopathy, anemia, and cardiomegaly, and underwent liver transplantation.
Functional: metabolomics analysis revealed that the exogenously introduced Gly62Glu mutant resulted in the downregulation of numerous metabolites involved in lipid metabolism pathway.

PMID: 29127204 Rujano et al., 2017
Report of 3 individuals from 2 families with two hemizygous missense mutations in ATP6AP2. Seq method: WES.
P1 - Portuguese male, hemizygous for the ATP6AP2:c.293T>C (p.L98S) variant. Liver biopsy at 16 mo of age showing cirrhosis and steatosis; recurrent infections noted.
P2, P3 - 2 males from a German family, hemizygous for a ATP6AP2:c.212G>A (p.R71H) variant. P2: recurrent pulmonary and upper respiratory tract infections throughout infancy and childhood; ultrasounds showed hepatosplenomegaly. P3: developed liver failure at 5 months of age, liver biopsy revealed lipid accumulation and enlarged vacuolar structures within hepatocytes; suffered from recurrent infections.
Functional: Authors also show that ATP6AP2 deficiency in the mouse liver caused hypoglycosylation of serum proteins and autophagy defects.

ATP6AP2 is associated with X-linked Congenital disorder of glycosylation, type IIr, OMIM:301045, Intellectual developmental disorder, X-linked syndromic, Hedera type, OMIM:300423, and ?Parkinsonism with spasticity, X-linked, OMIM:300911 (OMIM accessed 8th July 2026).
Sources: Literature

Created: 8 Jul 2026, 11:59 a.m. | Last Modified: 8 Jul 2026, 12:28 p.m.

Panel Version: 8.6

Mode of inheritance
X-LINKED: hemizygous mutation in males, biallelic mutations in females

Phenotypes
Congenital disorder of glycosylation, type IIr, OMIM:301045; congenital disorder of glycosylation, type IIr, MONDO:0026765; congenital disorder of glycosylation, type IIr, X-linked recessive

Publications

• 29127204
• 38075676
• 41131679

Mode of pathogenicity
Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments