Review Papers Claim by Claim

2.1 Loss-of-function PIEZO2 is directly shown in vitro

• Genetics: Both patients carry compound-inactivating PIEZO2 variants, including premature stop codons and a missense variant affecting the same codon. PIEZO2 variant types and segregation
• Functional expression: In HEK293 cells expressing mouse Piezo2 homologs, the truncated constructs are translated but nonfunctional (mechanically gated currents above baseline noise only seen for wild-type). HEK293 mechanogated current loss for truncated PIEZO2
• mRNA evidence: Skin biopsy RT-PCR suggests nonsense-mediated decay for Patient 1’s premature-stop alleles and predominantly normally spliced transcript from the missense allele for Patient 2. RT-PCR evidence for nonsense-mediated decay and allele-specific splicing

2.2 Interpretation of “selectivity” across mechanosensory modalities

• The paper reports selective loss for discriminative touch and vibration detection (especially glabrous + calibrated vibration), while pain thresholds and thermal detection are reported as broadly similar to controls in Patient 1 (and thermal thresholds similar in both). Reported preservation of pain/thermal thresholds
• They also show that on hairy skin the patients can detect slow gentle brushing (100% on hairy forearm) even while they are impaired for other mechanosensory tasks, suggesting that not all mechanotransduction in humans depends on PIEZO2. PIEZO2-dependent vs PIEZO2-independent brushing on hairy vs glabrous skin

2.3 A mechanistic “single-channel” inference may be too strong

• Sample size: Sensory testing comparisons were made between n=2 patients and small control cohorts (e.g., five controls for Patient 1 sensory testing; fewer for some tasks). The paper itself flags that small sample sizes should be taken into consideration when interpreting statistical inference. Authors acknowledge small sample sizes
• Multiple comparisons / operational specificity: Multiple sensory modalities and multiple force thresholds are evaluated; however, the excerpt does not show a global multiplicity correction strategy. This increases the risk that some p-values could reflect chance findings, especially for tasks with high variance or subjective ratings. (Uncited here because the excerpt doesn’t provide enough detail on correction procedures.)
• Subjective/behavioral dependence: Several tasks rely on participant reporting (e.g., thermal detection thresholds via verbal indication, proprioception direction forced-choice). Such measures can be influenced by attention, learning, expectation, and compensatory strategies. (Uncited here because the excerpt does not provide quantitative measures of blinding or observer bias controls.)
• Cell model generalization: HEK293 is used to test PIEZO2 channel function via mechanical gating, but the constructs are expressed in a heterologous system; the excerpt assumes strong sequence homology and conserved flanking regions (91% identical, 95% similar) to justify using mouse Piezo2 homologs. Homology rationale for heterologous HEK293 testing

• Discovery of a non-PIEZO2 genetic variant in the same individuals that more directly explains the sensory phenotype; or functional assays showing the variants retain PIEZO2 function in relevant mechanotransduction contexts (beyond HEK293). Causal inference hinges on loss-of-function PIEZO2
• Replicating the same behavioral/sensory pattern in additional patients with PIEZO2 loss-of-function variants (or showing consistent absence of such pattern when PIEZO2 is intact). (This point is general and therefore not separately cited from the excerpt.)

• Known (direct evidence in the excerpt): specific PIEZO2 variants exist in both patients and are predicted/assessed to be loss-of-function; the expressed truncated channel constructs produce no mechanically gated currents in HEK293; patients show specific deficits in punctate touch discrimination, vibration detection, and proprioception with increased reaching dysmetria under visual deprivation. Direct genetic/functional/behavioral evidence in the paper
• Inferred: PIEZO2-dependent mechanotransduction occurs at sensory afferent terminals and/or mechanoreceptor complexes that underlie the tested modalities; alternative mechanosensors can support other mechanosensory behaviors (e.g., slow brushing on hairy skin). Inferences from selective behavioral preservation
• Uncertain / needs broader replication: the degree to which PIEZO2 is quantitatively responsible for all mechanical transduction across all skin regions, all receptor subtypes, and all mechanical regimes; and the relative contributions of peripheral mechanotransduction vs central compensation in shaping the observed behavioral outcomes. The mouse mechanistic literature suggests compensation or channel redundancy may exist for some mechanosensitive current classes. Mouse data suggesting redundancy/compensation