Yes, InnoSer has verified and confirmed that the C3-PMP22 mouse model of CMT1A contains 5 copies of the human PMP22 transgene.  

The original publication of the C3-PMP22 mouse model originally estimated, using qPCR, that the C3 mouse line has 3-4 copies of the PMP22 transgene, hence its originally given name (Verhamme et al., 2011), from which the confusion about the model’s PMP22 gene copies sometimes remains to this day.  

Most recent analyses performed by InnoSer’s collaborators (Prior et al., 2024), using digital droplet PCR (ddPCR), a highly precise method for absolute DNA quantification, have shown that the C3 mouse line carries 5 copies of the PMP22 transgene, clarifying earlier qPCR-based estimates of 3–4 copies. This mouse model was also donated by the original developers to JAX, and the transgene copy numbers are also reflected in the JAX stock mice (JAX # 030052).  

At present, InnoSer works with a cryopreserved male founder colony that was established and confirmed to contain 5 copy genes of the PMP22 transgene, ensuring that experimental cohorts have the same genotype, supporting reproducibility and reliable interpretation of therapeutic efficacy.  

Reach out to our expert team to explore how you canleveragethe well-characterized C3-PMP22 model for your preclinical CMT1A studies. 

InnoSer has started working with the C3-PMP22 mouse model shortly after the model has been established in 2011 by our academic collaborators (Verhamme et al., 2011). Over the years, InnoSer’s scientific team has contributed to several pivotal studies led by our academic collaborators on its further characterization and use (Prior et al., 2024; Michailidou et al., 2023).  

As part of InnoSer’s preclinical neurology CRO work, our scientific experts have performed extensive phenotype validation experiments in-house, confirming its translational relevance and suitability for preclinical efficacy studies. InnoSer’s validated motor function readouts include both classical (Balance Beam, Rotarod, Grip Strength, Tremor, Extension Reflex) and automated (e.g., CatWalk gait analysis) behavioral tests.  

Importantly, these behavioral readouts are complemented by translationally relevant in vivo electrophysiology, including sciatic nerve conduction study (NCS)aimed to assess compound muscle action potential (CMAP) and nerve conduction velocity (NCV) measurements, which directly reflect peripheral nerve function and provide critical translational endpoints for evaluating the efficacy of potential CMT1A therapeutics. End-of-study readouts can also include sciatic nerve histology (using for e.g., quantification of G-ratio, which is a quantitative measure of myelination, using toluidine blue staining) and drug biodistribution within the sciatic nerve, supporting mechanistic insights and interpretation of functional outcomes.  

To date, InnoSer has leveraged this expertise and has carried out numerous sponsor preclinical efficacy studies of multiple candidate therapeutics for CMT1A.  

Let’s discuss how we can support your CMT1A preclinical program. Reach out to InnoSer’s scientific team, who will be happy to share and walk you through the validation data we have obtained in this CMT1A mouse model.  

While the C3-PMP22 mice do not display overt clinical signs at 3 weeks of age (Verhamme et al., 2011), early motor dysfunction is still detectable at ages of 3-4 weeks, when the first in vivo measurements (sciatic nerve electrophysiology, rotarod, grip strength) can be performed.  

This allows us to design preclinical efficacy studies either as prophylactic interventions, starting as early as PND1 (e.g., for viral vector administration) up to 4 weeks of age, or as symptomatic treatments, typically recommended to be initiated around 4 weeks of age. In line, study termination is usually planned based on the treatment initiation, with recommended endpoints at 9 or 12 weeks of age. The C3-PMP22 mouse model is actively bred in-house at InnoSer, allowing for PND1 dosing and relatively quick study start-up times. Combined with the model’s disease progression, this enables you to carry out relatively short, yet robust preclinical efficacy studies for novel CMT1A candidate therapeutics.  

Interested in running a CMT1A efficacy study with InnoSer? Reach out to our team today to obtain expert guidance on your study designs and start-up study timelines.

Charcot-Marie-Tooth (CMT) disease is characterized by peripheral nerve demyelination and axonal loss, impacting the speed at which nerve signals are transmitted as well as the muscle response. Nerve conduction study (NCV) measures both the speed at which nerve signals are transmitted as well as the strength of the muscle response and thus serves as the electrophysiological marker for myelin integrity in CMT. NCSs play an important role in the clinical setting to diagnose the (sub)type of CMT as well as assess the severity of the disease. Therefore, in preclinical animal studies, NCS provide you with highly translationally relevant data, helping to bridge preclinical to clinical outcomes.  

In mice, in vivo electrophysiological recordings are performed on the sciatic nerve, the largest nerve of the peripheral nervous system, supplying the mouse hind limb with both motoric and sensory fiber tracts, using needle electrodes. Compound muscle action potential (CMAP) measures the number and integrity of functional motor units, whereby lower CMAP response indicates fewer functional motor units. Nerve conduction velocity (NCV) measures the speed and nerve signal propagation, serving as a proxy marker for nerve myelination. With nerve damage, white matter is lost, which means it takes longer for the stimulus to reach the connected muscle.   

At InnoSer, we have demonstrated that compared to WT littermates, C3-PMP22 mice have significantly increased NCV latencies, indicating slower nerve conduction as well as significant reduction in CMAP amplitude, reflecting a loss of functional motor units and reduced muscle innervation from 3-4 weeks of age.  

Importantly, as an in vivo electrophysiological readout, NCS serve as a marker for disease progression and can be performed longitudinally in the same animal, providing valuable insights into the efficacy of your CMT1A candidate therapeutics over time. 

Interested in including sciatic nerve electrophysiology readouts in your next CMT1A preclinical efficacy study and don’t know where to start? Reach out to our expert scientific team to discuss the best timepoints to include NCS to assess the efficacy of your therapeutics, taking into account your candidate drug’s mechanism of action (MoA), timeline , and budget needs.

G-ratio analysis is one of the most important histopathological readouts for evaluating myelin integrity in preclinical CMT1A mouse models, as it provides a quantitative measure of peripheral nerve demyelination and remyelination.  

The g-ratio is defined as the ratio between the inner axonal diameter and the total outer fiber diameter (axon + myelin sheath) and is widely used in peripheral nerve biology as a quantitative indicator of myelin thickness . Therefore, increased g-ratio values indicate thinner myelin sheaths and therefore demyelination — a hallmark pathological feature of Charcot-Marie-Tooth disease type 1A (CMT1A) (Jun Li, 2017).  

At InnoSer, sciatic nerves collected from C3-PMP22 mice are processed using glutaraldehyde fixation, Epon resin embedding, and semi-thin (1 µm) sectioning, followed by toluidine blue staining. Quantitative g-ratio analysis is subsequently performed on high-resolution digital scans of sciatic nerve cross-sections using in-house developed semi-automated image analysis workflows, enabling robust and scalable assessment of myelin thickness across large preclinical efficacy studies. Typically, 100 randomly selected axons per mouse are quantified across multiple nerve sections to ensure reliable evaluation of peripheral nerve pathology. 

Importantly, while in literature the use of transmission electron microscopy (TEM) is frequently used to visualise the myelin ultrastructure at extremely high resolution (Verhamme et al., 2011), electron microscopy-based workflows are relatively low-throughput, labor-intensive, and difficult to scale for drug development studies involving larger animal cohorts.  

In contrast, InnoSer’s established semi-thin sectioning and digital pathology workflow provides quantitatively robust g-ratio measurements that are fully suitable for preclinical efficacy assessment. Moreover, similar semi-thin sectioning approaches for g-ratio quantification have been widely used and validated in the peripheral neuropathy literature (Kaiser et al., 2021). 

Importantly, using this approach, InnoSer has confirmed that compared to WT littermates, C3-PMP22 mice display clear demyelination phenotypes with significantly increased g-ratios already at 8 weeks of age, supporting the model’s translational relevance for evaluating novel therapies targeting myelin rescue and peripheral nerve integrity in CMT1A.  

Interested in incorporating quantitative sciatic nerve histopathology and g-ratio analysis into your preclinical CMT1A efficacy study? Reach out to InnoSer’s neuromuscular disease team to discuss study endpoints and pathology workflows tailored to your therapeutic programme.