PFBC (preferred modern term) = bilateral, symmetric brain calcifications (especially basal ganglia [globus pallidus > putamen/caudate] ± dentate nuclei, thalami, subcortical white matter, cerebellum) due to pathogenic genetic variants, after exclusion of secondary/metabolic causes. Historical "Fahr syndrome" often refers to secondary cases with neuro/psych features. Spectrum: incidental/asymptomatic (high penetrance for calcifications but incomplete for symptoms) → movement disorders, seizures, cognitive decline, psychiatric syndromes. ~67% of diagnosed cases symptomatic; male predominance in some cohorts.

🧾 Terminology (2025–2026 consensus)

Fahr’s disease: outdated/historical for primary genetic form.
Fahr’s syndrome: secondary calcifications (e.g. endocrine, toxic, infectious).
Primary Familial Brain Calcification (PFBC): current umbrella term for monogenic primary cases (AD or AR).

📊 Epidemiology & Inheritance

Very rare; true prevalence unknown (<1/1,000,000 in some estimates); incidental CT detections increasing with widespread imaging.
Inheritance: mostly autosomal dominant (~82% of genetically confirmed cases); autosomal recessive ~18%.
Age-dependent, incomplete penetrance & high variable expressivity - calcifications often present by 30s–40s, but symptoms may be absent despite high total calcification score (TCS); mean age of onset ~44 years (95% CI 36–51).

🧬 Genetics & Pathophysiology

Core mechanism: disrupted phosphate homeostasis (impaired transport/clearance), neurovascular unit (NVU)/BBB/pericyte dysfunction, or astrocytic integrity → perivascular calcium-phosphate (hydroxyapatite) deposition in deep grey matter, vessels, and parenchyma. Emerging: possible extracerebral deposits (e.g., skin as biomarker).

Gene	Inheritance	Protein / Function	Key Clinical Notes & Detection Rate
SLC20A2	AD	PiT-2 sodium-dependent phosphate importer	Most common (~17% detection; up to 40–50% in familial); movement disorders + psychiatric/cognitive prominent; higher TCS.
PDGFB / PDGFRB	AD	PDGF-B ligand & receptor-β; pericyte recruitment/BBB integrity	Early psychiatric/cognitive onset; widespread calcifications; NVU disruption.
XPR1	AD	Phosphate exporter (xenotropic)	Movement disorders ± neuropsychiatric; impaired efflux.
MYORG	AR	Astrocytic ER protein (glycosidase-like)	Earlier onset; extensive calcifications; ~17% detection in screened cohorts; higher TCS.
JAM2	AR	Junctional adhesion molecule 2 (tight junction/BBB)	Childhood–young adult onset; mixed neuro/psych phenotypes; NVU involvement.
NAA60	AR	N-alpha-acetyltransferase 60 (N-terminal acetylation)	Recognised ~2024; biallelic variants impair acetylation/SLC20A2 expression; emerging (~few % in series).
CMPK2	AR (debated)	Mitochondrial cytidine/uridine monophosphate kinase 2	Reported 2022; limited independent replication; role uncertain per 2025 reviews/meta-analyses.

Note: ~40–60% of cases have identifiable variant (highest yield SLC20A2 & MYORG per meta-analyses). ~50% remain genetically unsolved after full panel. Genetic testing: targeted panel or WES after negative secondary workup.

🧠 Clinical Presentation

Movement disorders (~55% prevalence): parkinsonism (most frequent; bradykinesia, rigidity, tremor, gait instability/falls), dystonia, chorea/athetosis, tremor, ataxia, dysarthria/dysphagia (advanced).
Seizures (focal/generalised; ~10–30%), headaches (migraine-like or tension-type).
Cognitive/psychiatric: executive dysfunction, memory impairment, dementia (subcortical pattern); depression, anxiety, psychosis, apathy (~cognitive impairment 45% [95% CI 36–55], psychiatric symptoms 31% [95% CI 17–46] per 2025 meta-analysis); often initial presentation (~40% in some reviews).
Other: pyramidal signs (rare), cerebellar features, speech/swallowing issues; adolescent/early-onset cases may present with acute psychosis or seizures.
Onset variable (typically 30s–60s, mean ~44); many asymptomatic despite extensive calcifications/TCS; no strong symptom-TCS correlation (age more predictive of TCS).

🆚 Primary vs Secondary Brain Calcification

Category	Details
Secondary (Fahr syndrome)	Causes: hypo/hyperparathyroidism, pseudohypoparathyroidism, pseudopseudohypoparathyroidism, mitochondrial disorders (e.g. MELAS), infections (TORCH, HIV, CMV), toxins (Pb, CO, Mn), radiation/chemo, vasculitis, CKD-MBD. Clues: abnormal Ca/PO4/PTH/vit D/Mg, systemic/multiorgan features, exposure history. Action: identify & treat reversible cause first (e.g. Ca + calcitriol for hypoPTH; may partially reverse calcifications).
Primary (PFBC)	Genes as above; normal metabolic labs; family history (often dominant); typical symmetric CT pattern. Clues: negative secondary screen, genetic confirmation. Action: genetics referral, counselling, symptomatic management; no curative Rx.

🖼 Imaging

CT head: gold standard - bilateral symmetric dense calcifications (basal ganglia predominant); quantify with total calcification score (TCS) if needed (higher in MYORG/SLC20A2; correlates better with age than symptoms).
MRI: T1 hyperintense / T2 hypointense; blooming on GRE/SWI; less sensitive for early/small calcifications than CT; useful for differentials (e.g. atrophy, infarcts).

Bilateral basal ganglia calcifications (CT) consistent with PFBC/Fahr pattern

🔬 Investigations (UK-oriented)

Labs (first-line): Ca, PO4, Mg, ALP, vitamin D, PTH; U&E, TFTs, B12/folate; coeliac screen if indicated; HIV/syphilis if risk factors; lactate if mitochondrial suspected.
If metabolic cause found: treat urgently (e.g. hypoPTH) and reassess imaging/symptoms (may improve).
Neuro: CT diagnostic; MRI brain (with SWI) for extent/differentials; EEG if seizures; neuropsych assessment if cognitive issues.
Genetics: PFBC panel (SLC20A2, PDGFB, PDGFRB, XPR1, MYORG, JAM2, NAA60 ± others) after negative secondary workup; cascade testing/family counselling; consider WES if panel negative.

🛠 Management

Principle: Exclude/treat reversible causes; otherwise symptomatic, multidisciplinary, supportive care (no disease-modifying therapy yet; trials targeting phosphate/BBB ongoing in research).

Secondary: e.g. hypoPTH → calcium + active vitamin D (calcitriol/alfacalcidol); endocrine/nephrology input; monitor Ca/PO4.
Motor: levodopa/carbidopa trial (partial/variable response in parkinsonism); dopamine agonists; botox for focal dystonia; amantadine/trihexyphenidyl for tremor/dystonia; physio/OT for gait/balance/falls prevention; mobility aids.
Seizures: standard ASMs (levetiracetam/valproate preferred; avoid those worsening parkinsonism); DVLA driving advice (UK: inform, may need licence review).
Psychiatric: SSRIs (e.g. sertraline), SNRIs, or atypicals (quetiapine/aripiprazole; start low/go slow due to EPS risk); psychiatry/neuropsych liaison; CBT if appropriate.
Support/Rehab: SLT for dysarthria/dysphagia (aspiration risk); neuropsychology input; social services/carers support; bone health monitoring (immobility risk); depression/anxiety screening.
Follow-up: annual neurology review (cognitive/motor/psych); repeat imaging if symptoms progress; genetic counselling updates.

📌 OSCE / Viva Tips

Basal ganglia calcifications on CT → **always exclude secondary causes first** (Ca/PO4/PTH/Mg/vit D mandatory).
Normal labs + family history + typical pattern → suspect PFBC → genetics referral (panel testing).
Symptoms do **not** correlate well with calcification load/TCS - counsel patients/families carefully (prognosis variable).
Management = **symptomatic + supportive**; prioritise seizures, gait/falls, mood; prevent complications (aspiration, fractures, depression).

🧭 Differential Diagnosis

Parkinson’s disease (levodopa-responsive, rest tremor, normal imaging).
Huntington’s (chorea, caudate atrophy, CAG repeat).
Vascular parkinsonism/multi-infarct dementia (stepwise, vascular RFs, MRI infarcts/white matter changes).
Mitochondrial cytopathies (MELAS/MERRF: lactic acidosis, stroke-like episodes, multisystem, ragged-red fibres).
Other NBIA (e.g. PKAN: eye-of-the-tiger sign); Aicardi-Goutières (infantile, interferon signature); Cockayne syndrome; mucopolysaccharidoses.

📈 Prognosis

Highly variable: some lifelong asymptomatic/minimally affected; others progressive disabling motor/cognitive/psychiatric disease (worsening over decades).
Secondary: often improves/stabilises with cause correction.
Primary PFBC: supportive Rx reduces morbidity (falls/fractures, aspiration pneumonia, severe mood disorders); life expectancy near-normal if managed well.

📚 References

GeneReviews: Primary Familial Brain Calcification Overview (updated Sep 18, 2025).
Yang D et al. Gene Variants Related to PFBC: Bibliometrics & Meta-Analysis. eNeuro 2025;12(6):ENEURO.0058-25.2025.
Keller A et al. Pathophysiology of Primary Familial Brain Calcification. Annu Rev Physiol 2026;88:273-296.
Manyam BV. What is and what is not “Fahr’s disease”. Parkinsonism Relat Disord 2005;11:73–80.
Nicolas G et al. Various reviews; Saleem S et al. Fahr’s syndrome: literature review. Orphanet J Rare Dis 2013;8:156.

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Primary Familial Brain Calcification (PFBC) Fahr Syndrome