| Diagnostic domain | Findings/tests | When used | Notes/pitfalls | Evidence source |
|---|---|---|---|---|
| Neurologic exam and developmental assessment | Congenital/early infantile hypotonia, truncal/cerebellar ataxia, delayed ambulation or non-ambulation, intellectual/developmental impairment, dysarthria, abnormal gait including quadrupedal or crawling patterns; assess head control, sitting, speech, coordination, ocular movements | First-line at initial clinical suspicion in infants/children with developmental delay and disequilibrium | Core syndrome is often recognizable clinically, but severity is variable across subtypes; some CAMRQ2/CAMRQ4 cases are milder than classic descriptions | (pqac-00000004, pqac-00000008, pqac-00000015, pqac-00000001) |
| Brain MRI: classic VLDLR-pattern | Inferior cerebellar vermis and hemisphere hypoplasia, small pons/brainstem, simplified cortical sulcation/gyral pattern, mildly thickened cortex | Early neuroimaging in children with congenital ataxia/intellectual disability | Highly suggestive of VLDLR-associated disease (CAMRQ1), but not all CAMRQ subtypes share this pattern | (pqac-00000004, pqac-00000008, pqac-00000017) |
| Brain MRI: ATP8A2-pattern | MRI may be normal or only mildly abnormal; reported findings include cerebellar atrophy, cerebral atrophy, thin/hypotrophic corpus callosum, delayed myelination, ventriculomegaly | Use in suspected CAMRQ4, especially when phenotype is severe but diagnosis unclear | Normal MRI does **not** exclude CAMRQ4; one cohort reported normal brain MRI in 60% of patients, so overreliance on MRI can delay diagnosis | (pqac-00000015, pqac-00000011, pqac-00000009, pqac-00000010, pqac-00000014) |
| Brain MRI: WDR81/CAMRQ2 pattern | Cerebellar atrophy or hypoplasia, corpus callosum hypoplasia/atrophy, generalized brain atrophy; vermian-predominant cerebellar atrophy in some cases | Use when CAMRQ2 is in differential for congenital ataxia with ID and gait abnormality | CAMRQ2 is very rare and neuroradiology may overlap with other cerebellar malformation syndromes | (pqac-00000001) |
| Ophthalmology | Fundoscopy/ophthalmic exam for optic atrophy, retinal degeneration, abnormal ocular movements, strabismus, ophthalmoplegia | Early in workup when CAMRQ4 or broader CAMRQ is suspected | Visual system involvement is particularly helpful for recognizing ATP8A2-related disease; ocular motor abnormalities also occur in other CAMRQ subtypes | (pqac-00000010, pqac-00000011, pqac-00000002, pqac-00000004) |
| Audiology | Auditory brainstem response (ABR) testing | When severe developmental delay/hypotonia with possible sensory impairment is present, especially in CAMRQ4 | Abnormal or flattened ABR can support ATP8A2-related disease and help distinguish from isolated cerebral palsy-like presentations | (pqac-00000010, pqac-00000025) |
| Electrophysiology | Somatosensory evoked potentials (SSEP); targeted EEG if seizures suspected | Adjunctive testing in severe CAMRQ4 or unexplained neurodevelopmental disorder | Flattened cortical SSEPs were reported in CAMRQ4; electrophysiology is supportive rather than diagnostic | (pqac-00000010, pqac-00000025) |
| Metabolic screening | Plasma/CSF biochemistry, urine organic acids/GC-MS, other metabolic tests to exclude treatable neurometabolic disorders | Early exclusionary step in infants/children with hypotonia, ataxia, developmental delay | Often normal in genetically confirmed CAMRQ; useful mainly to rule out mimics before/alongside genomic testing | (pqac-00000025, pqac-00000021) |
| Genetic testing strategy | Whole-exome sequencing (WES) or broad ataxia/neurodevelopmental panel; trio testing when possible; segregation by Sanger sequencing in relatives; ACMG/AMP variant classification; CNV analysis when indicated | Recommended once syndromic congenital ataxia/dysequilibrium is recognized or MRI/clinical clues suggest CAMRQ | Broad sequencing is especially important because CAMRQ is genetically heterogeneous (VLDLR, WDR81, CA8, ATP8A2) and MRI may be normal in CAMRQ4; reanalysis can be informative in rare subtypes | (pqac-00000015, pqac-00000009, pqac-00000021, pqac-00000001, pqac-00000023) |
| Differential diagnosis: dyskinetic cerebral palsy | Early non-progressive hypotonia, dyskinesia/choreoathetosis, severe motor delay may resemble dyskinetic CP | Consider during initial pediatric neurology assessment, especially in infancy | CAMRQ4 can mimic dyskinetic cerebral palsy early; associated visual/hearing impairment, family history/consanguinity, and genomic testing help distinguish it | (pqac-00000010, pqac-00000025) |
| Differential diagnosis: hereditary/nonprogressive congenital ataxias and cerebellar malformations | Distinguish from other recessive ataxias, pontocerebellar hypoplasia spectrum, Joubert-related disorders, and CA8-related ataxia with normal intellect | Use after initial MRI and exam narrow to congenital cerebellar disorder | Imaging-phenotype discordance can occur, especially CA8 and ATP8A2 cases with normal or subtle MRI findings | (pqac-00000021, pqac-00000027, pqac-00000015) |
| Diagnostic counseling/real-world implementation | Use molecular diagnosis to inform prognosis, recurrence risk, family testing, and educational/rehabilitative planning | After confirmation of pathogenic/likely pathogenic variants | Published cases document supportive services (special education, daily care support, PT in some cases), but no disease-specific diagnostic biomarker or targeted therapy is established | (pqac-00000021, pqac-00000025, pqac-00000001) |


*Table: This table summarizes the practical diagnostic workup and key differential diagnoses for cerebellar ataxia, intellectual disability, and dysequilibrium syndrome across major subtypes. It highlights where MRI is informative, where it may be misleading, and why broad genomic testing is central to diagnosis.*