Typical from father
Typical from mother
General information only
About Carbonic Anhydrase II deficiency
This content is for awareness and education only. It is not a substitute for medical advice, diagnosis, or specialist care.
What is Carbonic Anhydrase II deficiency?
It is a rare inherited condition linked to deficiency of the enzyme carbonic anhydrase II. Medical references also call it osteopetrosis with renal tubular acidosis. It is listed in OMIM as entry 259730 and in Orphanet as ORPHA:2785.
The classic description in those sources brings together increased bone density, renal tubular acidosis, and cerebral calcification. Not every person has every feature, and severity varies.
What is the CA2 gene?
CA2 is the gene that produces the enzyme carbonic anhydrase II. The enzyme speeds the reversible reaction between carbon dioxide and water on one side, and bicarbonate and hydrogen ions on the other.
This reaction helps regulate the body's acid-base balance. Carbonic anhydrase II also has an important role in kidney function, bone, and other tissues.
Carbonic anhydrase II deficiency usually occurs when disease-causing changes are present in both copies of CA2, because the condition is inherited in an autosomal recessive pattern.
There is no single variant in every affected person. Different CA2 changes have been documented. One of the most often reported among some Arab and Saudi patients is c.232+1G>A, historically called the Arabic mutation.
Genomic location of the CA2 gene
- Gene
- CA2
- Chromosome
- 8
- Region
- 8q21.2
- Coordinates
- 85,464,007–85,481,493
Reference assembly: GRCh38.p14
NCBI Gene ID: 760
OMIM Gene: 611492
OMIM Disease: 259730
The genomic coordinates above are based on the GRCh38.p14 reference assembly and may differ if another genome build is used.
How is it inherited?
Inheritance is autosomal recessive. A person with the condition has typically inherited a disease-causing change in both copies of CA2. Carrier parents usually do not have the condition themselves.
If both parents are carriers, the chance of a child inheriting both changed copies is estimated at 25% in each pregnancy. The condition is not contagious. Family-specific genetic questions belong with a genetics professional.
Father
gives one copy
Mother
gives one copy
Typical from father
Changed from mother
Changed from father
Typical from mother
Changed from father
Changed from mother
25% unaffected, not a carrier
50% unaffected carrier
25% affected
typical copy
changed copy
Each child receives one circle from the father and one from the mother. The chances start again with every pregnancy. This is an educational drawing, not a test result for any family.
Associated features
Published descriptions include a range of possible features. They are not a checklist that applies equally to everyone. Choose a feature to see the educational drawing.
Increased bone density
It may be associated with fractures, delayed tooth eruption, or craniofacial features. This drawing only illustrates the idea.
Renal tubular acidosis
Often described as a mixed pattern involving both proximal and distal tubular function.
Cerebral calcification
Described in many people, though it is not invariably present at every age.
Stature and development
Short stature, and developmental or learning differences, are described in some people.
Vision and hearing
Possible effects on vision or hearing if bone compresses cranial nerves.
A single feature does not make the diagnosis, and the absence of one feature does not exclude it. A clinical team connects the findings.
How is it diagnosed?
Diagnosis is made by specialist clinicians. Evaluation may include clinical assessment, blood and urine tests of acid-base balance, imaging, and genetic testing of CA2 in an accredited laboratory.
This website does not interpret laboratory results and cannot confirm or exclude a CA2 variant.
Follow-up and medical care
Care is individual and decided with the treating clinicians. Depending on the person, kidney, bone, neurology, eye, dental, and genetics specialists may be involved.
This site does not give doses, a treatment plan, or personal recommendations. Management of acidosis, bone disease, and neurologic or sensory follow-up belongs to the medical team.
Common questions
Is this the same as every form of osteopetrosis?
No. Osteopetrosis has several genetic causes. This page is only about the form linked to carbonic anhydrase II deficiency and CA2.
Can it spread to other people?
No. It is inherited, not contagious.
Will every child in a carrier family be affected?
No. Recessive inheritance has a chance with each pregnancy. A genetics professional can explain a specific family’s situation.
Does this website diagnose or treat?
No. Its role is awareness, trusted sources, and a route to a community that cares about the condition.
References
- OMIM. Osteopetrosis, autosomal recessive 3; OPTB3. #259730. omim.org/entry/259730
- OMIM. Carbonic anhydrase II; CA2. 611492. omim.org/entry/611492
- Orphanet. Osteopetrosis with renal tubular acidosis. ORPHA:2785. orpha.net
- NCBI Gene. CA2 carbonic anhydrase 2. Gene ID: 760. ncbi.nlm.nih.gov/gene/760
- Sly WS, et al. PNAS. 1983;80(9):2752-2756. PMID 6405388. PubMed