For researchers
Research Gaps
Justified research gaps drawn from this site’s Treatment, What We Know, and Global Evidence pages: why the question matters, what is known, and what remains unknown — not a funding list or treatment advice.
Last reviewed: September 2026
Library & evidence snapshot #
—Unique studies in the library
28Printable PDF files
2Languages (Arabic / English)
—Countries represented in evidence maps
Study and country metrics are filled from site data when available; we do not invent prevalence.
How to read these gap cards
Each card states why the question matters, what is known, what remains unknown, why we treat it as a gap with links into this site, who benefits, the clinical axis, a suggested research type, and short references (PMIDs or internal links).
Not a funding list, not a call for unethical trials, and not treatment advice.
Gaps are drawn from evidence limits this site already states on Treatment, What we know, and Global Evidence — not an invented global consensus.
HSCT outcomes in CA II: bone vs kidney vs neurologic axes
Transplant clinicians Bone Nephrology Researchers Transplant outcomes case series / long-term follow-up
Why it matters
Families and teams need a clearer picture of what may improve after transplant and what may persist, grounded in transparent selection and follow-up reporting.
What we know
Published CA II transplant evidence identified here is very small: PMID 11264157 reports two related BMT recipients, and PMID 38655726 adds one further HSCT case (about three transplanted patients across these two reports—not a global HSCT census). In the McMahon report, osteopetrosis resolved radiologically/histologically, RTA persisted, developmental delay persisted, hearing/vision stabilized in the reported children, and cerebral calcification developed after BMT in one child.
What remains unknown
These few published cases do not define who benefits most, adequate follow-up length, population-level effects on RTA or calcification trajectories, or CA II–specific selection standards. They also do not show that HSCT produces the same outcomes in every person with CA II.
Why we call this a gap
The Treatment — HSCT section cites these reports as the limited published base; the gap is that such small case evidence cannot answer selection, comparative efficacy, or long-horizon multi-organ questions.
Who benefits
Transplant clinicians, bone specialists, nephrologists, pediatricians, families considering the option, and study planners.
Clinical axis
Transplant outcomes · bone · renal tubular acidosis · nervous system · vision/hearing in selected severe cases
Research type
Transparent case series · long-term follow-up · outcome reporting with documented selection criteria
References
PMID 11264157 (McMahon et al., BMT; n=2 transplanted) · PMID 38655726 (additional HSCT case report, 2024)
See also: HSCT · Why HSCT does not fix everything · What we know
Genotype–phenotype correlation and residual activity (H107Y example)
Genetics Researchers Pediatrics genotype–phenotype study
Why it matters
Relating variant class to severity supports scientific communication and explains heterogeneity — without turning genotype into a prescription.
What we know
Published examples such as H107Y show reduced residual CA II activity with relatively milder features in a compound-heterozygous context (PMID 1542674)—an association, not a treatment rule. Broader mutation series document substantial allelic heterogeneity (PMID 15300855), and shared-genotype reports can still show wide clinical severity (PMID 8128957).
What remains unknown
Association is not validated individual prediction, and neither equals treatment prescription. There is no reliable model that maps genotype directly to a care plan; residual-activity assays are not routine; multicenter genotype–outcome datasets remain limited.
Why we call this a gap
H107Y, variant pathway, and What we know separate observed correlation from mutation-specific drug selection claims.
Who benefits
Clinical genetics, researchers, pediatricians, and families reading genetics reports.
Clinical axis
Genetics · clinical heterogeneity · residual enzyme activity
Research type
Genotype–phenotype study · multicenter cohorts · mechanistic assays when appropriate
References
PMID 1542674 (H107Y / residual activity) · PMID 15300855 (allelic / genotype–phenotype heterogeneity) · PMID 8128957 (phenotypic variability limits deterministic prediction) · internal: /en/treatment/#h107y
See also: Heterogeneity · What we know · Glossary
Long-term supportive care and renal outcome trajectories
Nephrology Families Pediatrics long-term follow-up
Why it matters
Most published care is supportive and individualized; families need clearer evidence on kidney, bone, and growth trajectories across years of follow-up.
What we know
Supportive care (including team-directed acid–base and electrolyte management) is the mainstay described on this site. Longer published follow-up in a sizable single-center CA II series (PMID 11938359) documents multi-year supportive-care trajectories better than transplant case reports alone; there is still no general approved algorithm for all CA II patients.
What remains unknown
Even with such series, harmonized lifetime renal complication rates, agreed follow-up endpoints, and multicenter comparative trajectories under supportive care remain incompletely answered.
Why we call this a gap
Supportive care, RTA, and What we know emphasize individualized care; existing long-term reports do not replace a prospective multicenter follow-up program.
Who benefits
Nephrologists, pediatricians, families, and follow-up study planners.
Clinical axis
Kidney · electrolyte disturbance · renal tubular acidosis · long-term follow-up · growth
Research type
Long-term follow-up · prospective cohort · multicenter registry
References
PMID 11938359 (long-term supportive / natural-history follow-up) · internal: Supportive care · What we know · secondary contrast only: PMID 11264157 (RTA persisted after BMT in that transplant report)
See also: Family toolkit · Treatment gaps
Neurologic outcomes and cerebral calcification trajectory
Neurology Families Researchers natural history / imaging follow-up
Why it matters
Cerebral calcification appears in many published reports, yet families ask whether the trajectory is inevitable and how it changes over time or after interventions such as HSCT.
What we know
Imaging-focused reports describe intracranial calcification timing and progression in CA II (PMID 2413500). Longer clinical series also note progressive calcification in some patients under follow-up (PMID 11938359). Separately, one published BMT recipient developed cerebral calcification after transplant (PMID 11264157)—a transplant-context observation, not the primary natural-history source.
What remains unknown
Existing reports do not provide standardized imaging follow-up maps linking calcification timing to neurologic function across centers, or prove whether specific interventions alter the trajectory for most patients.
Why we call this a gap
About the disease, HSCT, and What we know mention calcification without claiming inevitability at every age or for every patient; published imaging series still leave protocolized natural-history questions open.
Who benefits
Neurologists, pediatricians, families, and natural-history researchers.
Clinical axis
Nervous system · development · long-term follow-up
Research type
Natural history study · long-term imaging follow-up · outcome reporting
References
PMID 2413500 (calcification timing/progression) · PMID 11938359 (longer follow-up context) · PMID 11264157 (post-BMT calcification in one reported transplanted child) · About the disease
See also: Glossary — calcification · What we know
Natural history and the need for a multicenter registry
Researchers Future study planners Pediatrics multicenter registry
Why it matters
The condition is rare; without organized multi-center data it is hard to describe trajectories, complications, and timing of interventions reliably.
What we know
This site aggregates published evidence through the library and Global Evidence maps, but it is not a clinical patient registry and does not present prevalence.
What remains unknown
Age-related event rates, multi-organ phenotype variability in larger samples, and harmonized outcome definitions remain explicit gaps.
Why we call this a gap
Global Evidence, the library, and What we know show the limits of inferences from indexed literature alone.
Who benefits
Researchers, study planners, scientific boards, and multidisciplinary clinics.
Clinical axis
Long-term follow-up · multi-organ heterogeneity · natural history
Research type
Multicenter registry · natural history study · standardized outcome sets
References
Internal: Global Evidence · Academic library · For researchers
See also: What we know · Collaborate
Quality of life and family-reported outcomes
Families Pediatrics Researchers patient/family-reported outcomes
Why it matters
Care is more than laboratory numbers; medication burden, school life, pain, and family stress are clinically relevant yet rarely measured in CA II literature.
What we know
This site offers family organizing tools (care toolkit) and community stories without claiming disease-specific validated QoL instruments.
What remains unknown
There are no CA II–specific, validated patient/family-reported outcome tools, and few studies link such measures to long-term medical trajectories.
Why we call this a gap
Family toolkit, For families, and What we know highlight family needs while keeping published-evidence limits visible.
Who benefits
Families, pediatricians, support services, and designers of future studies.
Clinical axis
Quality of life · long-term follow-up · family support
Research type
Patient/family-reported outcomes · mixed-methods follow-up
References
Internal: Family toolkit · Community stories · For families
See also: What we know · FAQ
Limits of geographic distribution in indexed evidence
Researchers Future study planners epidemiologic mapping limits
Why it matters
Country maps help show where indexed cases were published; reading them as global prevalence misleads research and health planning.
What we know
Global Evidence links literature to published/indexed locations and shows geographic representation of evidence — with an explicit notice that it is not a prevalence measure.
What remains unknown
True prevalence, unpublished cases, and under-represented regions remain unknown from site data alone.
Why we call this a gap
Global Evidence states maps are literature-linked, not prevalence; the library reflects what was indexed.
Who benefits
Researchers, study planners, and public-health readers who interpret evidence maps cautiously.
Clinical axis
Geographic representation of evidence · publication bias
Research type
Broader case ascertainment · registry participation from under-represented regions · transparent mapping methods
References
Internal: Global Evidence · Library
See also: What we know · Saudi Arabia
Do not generalize other osteopetrosis therapies to CA II deficiency
Bone Transplant clinicians Researchers differential evidence
Why it matters
Mixing osteopetrosis disease types can encourage inappropriate trials or prescribing; mechanistic differentiation is required before importing interventions from other literatures.
What we know
Therapies discussed for other osteopetrosis forms (for example interferon-γ or bisphosphonates) should not be imported as routine CA II care without CA II–specific evidence. This is a methodological caution about disease differentiation—not a claim that those agents have been proven ineffective in CA II trials.
What remains unknown
Clear comparative studies of responses across osteopetrosis types, and limits of protocol transfer, are still needed before any generalization.
Why we call this a gap
Treatment places the warning inside CA II–specific evidence framing; the gap is missing disease-specific comparative evidence—not a recommendation to use those drugs.
Who benefits
Bone specialists, transplant teams, pediatricians, and researchers in genetic bone disease.
Clinical axis
Bone · treatment outcomes · diagnostic differentiation
Research type
Comparative reviews · disease-specific outcome studies · cautious case reporting
References
Internal: Treatment page · What we know (no PMID assigned here for interferon-γ/bisphosphonate non-use; HSCT papers do not test those therapies)
See also: Glossary — osteopetrosis · Treatment gaps
Also see: What we know · Treatment gaps · Researchers hub · Library · Global Evidence