On January 23, 2024, Vanda Pharmaceuticals (VNDA) announced that its antisense nucleotide (ASO) drug VCA-894A targeting the IGHMBP2 gene has officially received FDA's Investigational New Drug (IND) approval.[1] This marks VCA-894A as another innovative therapy targeting IGHMBP2 to receive clinical approval, following the AAV9-IGHMBP2 gene replacement therapy developed by Alcyone Therapeutics.[2] VCA-894A is a novel ASO specifically designed for the splicing site mutations of the IGHMBP2 gene, which cause loss of motor neurons and degeneration of the peripheral nervous system, leading to a rare disease called Charcot-Marie-Tooth type 2S (CMT2S), also known as peroneal muscular atrophy type 2S, first defined in 2014.[3] Currently, clinical trial-stage treatments targeting IGHMBP2 encompass gene therapy and small nucleic acid drugs, while other therapies such as stem cell transplantation are also actively under development.[4-7]

Two clinically distinct diseases have been associated with IGHMBP2 gene mutations: spinal muscular atrophy with respiratory distress type 1 (SMARD1) and Charcot-Marie-Tooth type 2S (CMT2S). Humanizing the mouse gene and introducing clinically relevant mutations enable our next-generation HUGO-GTTM mouse models to develop a CMT2S-like phenotype that replicates the genetic basis of the disease and potential treatments. The HUGO-GTTM B6-hIGHMBP2 mouse model effectively expresses the human IGHMBP2 gene while not expressing the endogenous mouse Ighmbp2 gene, resulting in significant expression of the human gene in vivo. Therefore, this model can be utilized for studying neuron diseases related to the IGHMBP2 gene, such as Charcot-Marie-Tooth disease (CMT) and SMARD1.

The Structure and Biological Functions of the IGHMBP2 Protein

Immunoglobulin helicase μ-binding protein 2 (IGHMBP2), also known as cardiac transcription factor 1 (CATF1), is an ATP-dependent DNA/RNA helicase enzyme that is encoded by the IGHMBP2 gene. It possesses multiple structural domains, including DNA/RNA helicase domain, R3H single-stranded nucleic acid binding domain, and zinc finger domain. IGHMBP2 belongs to the AAA+ ATPase superfamily and can attach to specific regions of DNA, temporarily unwinding the DNA double helix.[8] Thus, IGHMBP2 plays regulatory roles in processes such as DNA replication, repair, and transcription, as well as RNA metabolism, splicing, protein translation, etc. It plays a crucial role in the survival of motor neurons, nervous system development and maintenance, and the maintenance of normal cardiac function.

Figure 1: IGHMBP2 protein regulates transcription and translation processes through various mechanisms.[8]

IGHMBP2 Gene mutations lead to CMT2S and SMARD1

IGHMBP2 gene mutations can lead to two clinically distinct diseases, spinal muscular atrophy with respiratory distress type 1 (SMARD1) and Charcot-Marie-Tooth type 2S (CMT2S).

Spinal Muscular Atrophy With Respiratory Distress Type 1

SMARD1 primarily affects α-motor neurons in the anterior horn of the spinal cord and is characterized by early-onset muscle weakness and respiratory distress in infants. Symptoms typically manifest within the first few months after birth, including weakness of the diaphragm and other respiratory muscles, diminished reflexes, swallowing difficulties, and motor impairment. SMARD1 has an acute onset and rapid progression, which can lead to peripheral respiratory failure and be life-threatening.[9]

Charcot-Marie-Tooth Disease Axonal Type 2s

CMT2S is a subtype of Charcot-Marie-Tooth disease (CMT), which is a hereditary neuropathy affecting the peripheral nervous system. The incidence of CMT2S is less than 1/1,000,000 and primarily manifests within the first decade of life. It is characterized by muscle weakness and atrophy in the distal limbs, sensory loss, and weakened or absent tendon reflexes.[10-11] Compared to SMARD1, CMT2S involves the peripheral nervous system, has a milder phenotype, is typically non-fatal, and generally does not cause respiratory difficulties (dyspnea) or loss of spinal motor neurons.


Figure 2: Clinical features of SMARD1.[9]

IGHMBP2 Mutation Types And Locations Correlate With Disease Types And Severity

The location of mutations in the IGHMBP2 gene significantly influences the disease type and phenotype severity. Non-truncating mutations occurring in two RecA-like domains of the IGHMBP2 gene (1A and 2A) are the main pathogenic mutation types causing SMARD1, while truncating mutations in the last exon of the IGHMBP2 gene are the main cause for CMT2S. In the pathogenesis of SMARD1, the helicase domain of the IGHMBP2 protein plays a critical role. Most pathogenic mutations in SMARD1 occur in this helicase domain, leading to loss of ATPase or helicase activity.[12] Typically, loss-of-function mutations that result in complete mRNA degradation are more likely to cause a more severe SMARD1 phenotype.

In contrast, the occurrence of CMT2S is mainly associated with nonsense mutations in the 5' untranslated region (UTR) of the IGHMBP2 gene and frameshift, truncating, missense, and compound heterozygous mutations in the last exon.[13]


Figure 3: Distribution of non-truncating mutations (A) and truncating mutations (B) in the gene structure and protein functional regions of IGHMBP2.[13]

Preclinical research models for IGHMBP2-related diseases

IGHMBP2 is a relatively "mysterious" protein. Despite its recognized importance as a helicase, its specific role in cellular processes remains unclear. Although the gene is expressed systemically throughout the body, mutations primarily affect only neuronal cells, leading to specific neuronal diseases such as SMARD1 and CMT2S. Currently, there are no approved effective therapies for these IGHMBP2-related diseases, highlighting the need for further research.

Neuromuscular Degeneration Mouse Models

Neuromuscular degeneration (NMD) mice have served as the primary research models for studying SMARD1. In these mice, a spontaneous mutation occurs in the fourth intron of the Ighmbp2 gene, resulting in abnormal splicing in nearly 80% of transcripts. This leads to a significant reduction in full-length Ighmbp2 mRNA levels and results in a phenotype resembling SMARD1. However, respiratory distress in NMD mice is not caused by neuronal degeneration but rather by diaphragmatic defects. Additionally, cardiac cell death in NMD mice leads to cardiomyopathy and heart failure, which may be an early cause of mortality but is not observed in SMARD1 patients. Thus, NMD mice exhibit significant differences from human SMARD1, particularly in terms of respiratory distress and lethality.[14]

Future Research Requires Genetic Humanization Modeling

Furthermore, IGHMBP2 gene mutations also lead to CMT2S, but most mouse models currently fail to replicate the clinical features of this disease. To induce a CMT2S-like phenotype in mice, it is necessary to humanize the mouse gene and introduce clinically relevant mutations enabling the mice to develop a CMT2S-like phenotype that replicates the genetic basis of the disease.[15] Therefore, humanized mouse models play a significant role in advancing research on IGHMBP2 gene-related diseases such as SMARD1 and CMT2S.

IGHMBP2 gene humanized model - B6-hIGHMBP2 mouse

To address the research needs for IGHMBP2 gene-related diseases such as SMARD1 and CMT2S, particularly in therapies requiring precise targeting of human genes such as small nucleic acid drugs and gene therapy, Cyagen has developed the IGHMBP2 gene humanized model B6-hIGHMBP2 mouse (Product ID: C001437). In this HUGO-GTTM model, the human IGHMBP2 gene is site-specifically replaced in situ at the mouse Ighmbp2 gene locus, containing all base sequences from the promoter to the 3'UTR. The mice successfully express the human IGHMBP2 gene without expressing the mouse Ighmbp2 gene. This model can be utilized for studying therapies targeting the human IGHMBP2 gene or protein. Furthermore, it can serve as a basis for constructing models with clinical pathogenic mutations, enabling the evaluation of gene therapy or small nucleic acid therapies tailored to specific patient mutation types, thus achieving personalized precision medicine.



Figure 4: Detection of gene expression in vivo in C57BL/6NCya wild-type mice and B6-hIGHMBP2 mice.

Conclusions

The B6-hIGHMBP2 mouse model (Product ID: C001437) effectively expresses the human IGHMBP2 gene while not expressing the endogenous mouse Ighmbp2 gene, resulting in significant expression of the human gene in vivo. Therefore, this model can be utilized for studying neuron diseases related to the IGHMBP2 gene, such as Charcot-Marie-Tooth disease (CMT) and spinal muscular atrophy with respiratory distress type 1 (SMARD1). Cyagen utilizes its proprietary TurboKnockout fusion BAC recombination technology to provide hot-spot mutation disease models based on this model. Customized services are also available based on different point mutations to meet researchers' needs for drug screening and pharmacological experiments related to diseases such as CMT and SMARD1.

Additionally, Cyagen has developed a variety of humanized and humanized point mutation models in other areas of neurodegenerative diseases and neuromuscular diseases to meet the research needs for small nucleic acid and gene therapies in these fields.

Contact us for a free consultation on your model customization project to see how we can enhance your preclinical research.

 

References:

[1] Vanda Pharmaceuticals. (2024, February 1). Vanda Pharmaceuticals Receives FDA Approval to Proceed with Investigational New Drug VCA-894A, a Novel Antisense Oligonucleotide Candidate for the Treatment of Charcot-Marie-Tooth Disease Type 2S. BioSpace. https://www.biospace.com/article/releases/vanda-pharmaceuticals-receives-fda-approval-to-proceed-with-investigational-new-drug-vca-894a-a-novel-antisense-oligonucleotide-candidate-for-the-treatment-of-charcot-marie-tooth-disease-type-2s/

[2] Cottenie E, Kochanski A, Jordanova A, Bansagi B, Zimon M, Horga A, Jaunmuktane Z, Saveri P, Rasic VM, Baets J, Bartsakoulia M, Ploski R, Teterycz P, Nikolic M, Quinlivan R, Laura M, Sweeney MG, Taroni F, Lunn MP, Moroni I, Gonzalez M, Hanna MG, Bettencourt C, Chabrol E, Franke A, von Au K, Schilhabel M, Kabzińska D, Hausmanowa-Petrusewicz I, Brandner S, Lim SC, Song H, Choi BO, Horvath R, Chung kW, Zuchner S, Pareyson D, Harms M, Reilly MM, Houlden H. Truncating and missense mutations in IGHMBP2 cause Charcot-Marie Tooth disease type 2. Am J Hum Genet. 2014 Nov 6;95(5):590-601.

[3] ClinicalTrials.gov. (2024, February 1). NCT05152823. ClinicalTrials.gov. https://beta.clinicaltrials.gov/study/NCT05152823?cond=CMT2S&checkSpell=false&rank=1

[4] Sierra-Delgado JA, Sinha-Ray S, Kaleem A, Ganjibakhsh M, Parvate M, Powers S, Zhang X, Likhite S, Meyer K. In Vitro Modeling as a Tool for Testing Therapeutics for Spinal Muscular Atrophy and IGHMBP2-Related Disorders. Biology (Basel). 2023 Jun 16;12(6):867.

[5] Shababi M, Feng Z, Villalon E, Sibigtroth CM, Osman EY, Miller MR, Williams-Simon PA, Lombardi A, Sass TH, Atkinson AK, Garcia ML, Ko CP, Lorson CL. Rescue of a Mouse Model of Spinal Muscular Atrophy With Respiratory Distress Type 1 by AAV9-IGHMBP2 Is Dose Dependent. Mol Ther. 2016 May;24(5):855-66. 

[6] Nizzardo M, Simone C, Rizzo F, Salani S, Dametti S, Rinchetti P, Del Bo R, Foust K, Kaspar BK, Bresolin N, Comi GP, Corti S. Gene therapy rescues disease phenotype in a spinal muscular atrophy with respiratory distress type 1 (SMARD1) mouse model. Sci Adv. 2015 Mar 13;1(2):e1500078. 

[7] Shababi M, Villalón E, Kaifer KA, DeMarco V, Lorson CL. A Direct Comparison of IV and ICV Delivery Methods for Gene Replacement Therapy in a Mouse Model of SMARD1. Mol Ther Methods Clin Dev. 2018 Aug 17;10:348-360.

[8] Rzepnikowska W, Kochański A. Models for IGHMBP2-associated diseases: an overview and a roadmap for the future. Neuromuscul Disord. 2021 Dec;31(12):1266-1278.

[9] Perego MGL, Galli N, Nizzardo M, Govoni A, Taiana M, Bresolin N, Comi GP, Corti S. Current understanding of and emerging treatment options for spinal muscular atrophy with respiratory distress type 1 (SMARD1). Cell Mol Life Sci. 2020 Sep;77(17):3351-3367. 

[10] Peng Guo, Beisha Tang, Guohua Zhao, et al. Pathological characteristics and genetic mutations of peroneal muscular atrophy. Chinese Medical Journal, 2005, 85(34): 2382-2385.

[11] Orpha.net. (2024, February 1). OC_Exp.php?lng=EN&Expert=443073. Orpha.net. https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=443073

[12] Saladini M, Nizzardo M, Govoni A, Taiana M, Bresolin N, Comi GP, Corti S. Spinal muscular atrophy with respiratory distress type 1: Clinical phenotypes, molecular pathogenesis and therapeutic insights. J Cell Mol Med. 2020 Jan;24(2):1169-1178. 

[13] Tian Y, Xing J, Shi Y, Yuan E. Exploring the relationship between IGHMBP2 gene mutations and spinal muscular atrophy with respiratory distress type 1 and Charcot-Marie-Tooth disease type 2S: a systematic review. Front Neurosci. 2023 Nov 17;17:1252075.

[14] Rzepnikowska W, Kochański A. Models for IGHMBP2-associated diseases: an overview and a roadmap for the future. Neuromuscul Disord. 2021 Dec;31(12):1266-1278.

[15] Martin PB, Holbrook SE, Hicks AN, Hines TJ, Bogdanik LP, Burgess RW, Cox GA. Clinically relevant mouse models of Charcot-Marie-Tooth type 2S. Hum Mol Genet. 2023 Apr 6;32(8):1276-1288. 

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