Can Childhood Metabolic Disorders Actually Lead to Heart Failure? Gene Therapy Research Provides Hope

Have you ever encountered patients who, despite growing normally during early childhood, gradually begin to exhibit symptoms such as facial abnormalities, growth retardation, delayed intellectual development, skeletal deformities, neurological abnormalities, and cardiac involvement? These symptoms are indicative of complex multisystem disorders caused by metabolic abnormalities. These disorders involve the interaction of multiple genetic and environmental factors and typically affect various body systems, including the nervous, endocrine, digestive, skeletal, and cardiovascular systems.

Currently, treatments for these childhood metabolic disorders primarily target their clinical manifestations rather than their underlying genetic defects. As a result, patients usually require lifelong treatment. To better understand the pathogenesis of these metabolism-related diseases and explore potential treatment methods, it is essential to establish animal models that can comprehensively replicate human diseases. These models will provide crucial tools for understanding the pathogenesis of these metabolism-related diseases and developing novel therapeutic approaches. By doing so, we can work towards improving the lives of those affected by these disorders.

Mucolipidosis Type II (ML II): Gene Therapy Research Progress

Mucolipidosis is a group of lysosomal storage disorders caused by defects in lysosomal enzymes, resulting in impaired breakdown of mucopolysaccharides and other various materials. This type of disorder leads to the accumulation of these molecules within cells, blood, and connective tissues, giving rise to a range of clinical phenotypes. Mucolipidosis can be classified into seven main types, and several subtypes. Among them, Mucolipidosis Type II (ML II) and Mucolipidosis III alpha/beta (ML IIIα/β) are both caused by mutations in the GNPTAB gene.

The GNPTAB gene encodes N-acetylglucosamine-1-phosphotransferase, which plays a critical role in the glycosylation and targeting of lysosomal proteins. Mutations in this gene lead to impaired enzyme function, subsequently affecting the normal function of lysosomes. Patients with these types of diseases exhibit symptoms such as growth retardation, delayed intellectual development, facial abnormalities, skeletal deformities, neurological abnormalities, and often suffer from heart failure due to cardiac involvement ^[1].

The Gnptab knockout (KO) mouse model developed by Paton et al., faithfully replicates the pathology of human ML II, displaying features such as growth retardation, skeletal and facial abnormalities, increased lysosomal enzyme activity, intracellular lysosomal storage, and shortened lifespan ^[2]. Ko et al., using gene-editing technology, created Gnptab-KO mice by deleting exons 12 to 22 of the Gnptab gene, which also presented various disease phenotypes resembling ML II, representing its pathological progression. Additionally, expressing the Gnptab gene via recombinant viral vectors in these mice resulted in significant therapeutic benefits, providing further insights into gene therapy for this type of inherited metabolic disorder ^[3].

Figure 1: The Gnptab homozygous knockout (KO) mice (-/-) exhibit phenotypes characterized by growth retardation and facial deformities as compared to WT (+/+) ^[3].

Muscular Dystrophy-Dystroglycanopathy A3: POMGNT1 Gene Knockout Mouse Model for Research

Muscle-Eye-Brain disease (MEB), also known as Muscular Dystrophy-Dystroglycanopathy A3 (MDDGA3), is a rare congenital muscular dystrophy (CMD) caused by mutations in amino acid metabolism enzyme genes. Its main features include hypotonia at birth, muscle dystrophy, central nervous system abnormalities, and eye abnormalities in patients. MEB is caused by homozygous or heterozygous mutations in the POMGNT1 gene, which encodes the protein O-mannose β-1,2-N-acetylglucosaminyltransferase (POMGnT1). POMGnT1 is involved in synthesis of O-mannose glycans and plays a critical role in the oxidative glycosylation modification of α-dystroglycan (α-DG), which is essential for stabilizing muscle fiber membrane and connecting the actin cytoskeleton with extracellular matrix. Therefore, mutations in the POMGNT1 gene lead to impaired O-mannose glycan synthesis, resulting in reduced glycosylation of α-DG and subsequently causing MDDGA3^[4].

Currently, physical therapy can help improve muscle strength and coordination, and antibiotics, corticosteroids, vitamin B1, vitamin B12, and adenosine triphosphate (ATP) can be used to aid in patient recovery. Acupuncture can also be used to alleviate eye muscle paralysis. However, there is currently no effective cure for this condition.

In mice, the loss of POMGnT1 leads to developmental defects in muscles, eyes, and the brain. Other phenotypes include congenital, non-progressive, mild to moderate sensorineural hearing loss, and severe abnormalities in myelin sheath formation in peripheral segments of the cochlear nerve. Additionally, POMGnT1-deficient mice show reactive gliosis in the retina, involving Müller glial cells and astrocytes ^[5-7]. These mice exhibit disease phenotypes similar to human MDDGA3, making them valuable tools for studying mechanisms of disease and drug development.

Figure 2: POMGnT1-deficient (-/-) mice exhibit a smaller cerebellum compared to WT (+/+) ^[5].

Wolfram Syndrome: Wfs1 and Wfs2 Gene Knockout Mouse Models

Wolfram syndrome, also known as DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy, and deafness) syndrome, is a rare autosomal recessive disorder characterized by the aforementioned symptoms.

The features of Wolfram syndrome include juvenile-onset diabetes and diabetes insipidus, along with progressive optic atrophy, hearing loss, and neurodegeneration. According to the International Classification of Diseases (ICD-11), Wolfram syndrome is classified as a rare specified diabetes mellitus (subcategory 5A16.1, Wolfram Syndrome). Currently, there are no effective treatments to delay or reverse the progression of Wolfram syndrome. Clinical monitoring and supportive care can help alleviate patients' suffering and improve their quality of life. The symptoms associated with this condition typically appear in childhood and early adulthood, with diabetes and visual problems happening before the age of 15, and ultimately lead to premature death due to brain dysfunction.

Wolfram syndrome is caused by autosomal recessive genetic mutations, and two genes related to the syndrome have been identified: WFS1 and WFS2, corresponding to Wolfram syndrome type 1 and Wolfram syndrome type 2, respectively ^[8].

Wfs1 gene knockout (KO) mice exhibit various phenotypic features associated with Wolfram syndrome, including diabetes (hyperglycemia, impaired glucose tolerance, and pancreatic dysfunction) ^[9-10], optic atrophy (progressive visual loss due to degeneration of optic nerve and retinal ganglion cells) ^[11], diabetes insipidus (polyuria and thirst caused by defects in antidiuretic hormone synthesis or secretion), as well as neurological abnormalities (motor coordination and balance disturbances, accompanied by behavioral and emotional disorders) ^[12]. The phenotypic features in Wfs1 KO mice provide crucial insights into understanding the pathogenesis of Wolfram syndrome and exploring potential therapeutic approaches.

Figure 3: Wfs1-deficient (Wfs1 KO) mice exhibit progressive loss of pancreatic beta cells ^[9].

Congenital Chloride Diarrhea (CLD): SLC26A3 Knockout Mouse Model for Gene Therapy Research

Congenital Secretory Chloride Diarrhea (a.k.a. Congenital Chloride Diarrhea, CLD) is a rare autosomal recessive genetic disorder characterized by watery diarrhea, high chloride ion content in feces, metabolic alkalosis, and electrolyte imbalances. Current treatments primarily target the symptoms rather than underlying genetic defects. Early diagnosis and proactive salt replacement therapy can achieve normal growth and development for patients. Sodium chloride and potassium chloride replacement therapies are also effective for children. However, these current treatments do not fix the underlying genetic defect, so treatment must be continued throughout the patient’s lifespan.

CLD is caused by mutations in SLC26A3 gene, which encodes a membrane protein in intestinal cells. Mutations result in loss of function of the protein, leading to reduced acidification and fluid absorption in gastrointestinal tract, and result in abundant watery diarrhea and metabolic alkalosis, often accompanied by secondary hyperaldosteronism ^[13].

Slc26a3 knockout (KO) mice exhibit low osmolarity mortality shortly after birth, while surviving mice display typical clinical features of CLD, including high chloride content diarrhea, growth retardation, colonic dilation, abnormal colonic epithelial growth patterns, significantly expanded colonic crypt proliferative zones, and increased plasma aldosterone ^[14].

Figure 4: Lack of ion transporter expression and activity in the colon of Slc26a3 knockout (KO) mice (-/-) leads to chloride ion dysregulation ^[14].

Rare Disease Research Resources: Genetically Engineered Mice by Cyagen

Genetically engineered mouse models play a crucial role in studying mechanisms of rare diseases and also evaluating drug efficacy. Cyagen provides thousands of self-developed gene-edited mouse strains, including knockout & conditional knockout models for disease-relevant genes (e.g. GNPTAB, POMGNT1, WFS1, and SLC26A3) that enable advancements in preclinical gene therapy research. Additionally, we also offer specialized customized services tailored to your research model development needs, helping accelerate your research projects.

Recommended Metabolic Models & Cyagen Custom Model Services

With the increased aging of society and prevalence of obesity, the incidence of metabolic diseases is increasing year over year, posing a serious threat to global human health. Cyagen's drug screening and evaluation platform can provide you with a variety of gene-edited mice that may be used to model metabolic disorders and assist in drug development research, such as Ldlr KO (em), Lep KO, Uox-KO (Prolonged), Atp7b KO, and Foxj1 KO mouse models.

Selected Models of Metabolism and Cardiovascular Diseases - Genome Editing Models

Selected Models of Metabolism and Cardiovascular Diseases – Drug-Induced Models

References:

[1]Leroy JG, Cathey SS, Friez MJ. GNPTAB-Related Disorders. 2008 Aug 26 [updated 2019 Aug 29]. In: Adam MP, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993–2023.

[2]Paton L, Bitoun E, Kenyon J, Priestman DA, Oliver PL, Edwards B, Platt FM, Davies KE. A novel mouse model of a patient mucolipidosis II mutation recapitulates disease pathology. J Biol Chem. 2014 Sep 26;289(39):26709-26721. doi: 10.1074/jbc.M114.586156. Epub 2014 Aug 8. 

[3]Ko AR, Jin DK, Cho SY, Park SW, Przybylska M, Yew NS, Cheng SH, Kim JS, Kwak MJ, Kim SJ, Sohn YB. AAV8-mediated expression of N-acetylglucosamine-1-phosphate transferase attenuates bone loss in a mouse model of mucolipidosis II. Mol Genet Metab. 2016 Apr;117(4):447-55. 

[4]Shenoy AM, Markowitz JA, Bonnemann CG, Krishnamoorthy K, Bossler AD, Tseng BS. Muscle-Eye-Brain disease. J Clin Neuromuscul Dis. 2010 Mar;11(3):124-6.

[5]Liu J, Ball SL, Yang Y, Mei P, Zhang L, Shi H, Kaminski HJ, Lemmon VP, Hu H. A genetic model for muscle-eye-brain disease in mice lacking protein O-mannose 1,2-N-acetylglucosaminyltransferase (POMGnT1). Mech Dev. 2006 Mar;123(3):228-40.

[6]Morioka S, Sakaguchi H, Mohri H, Taniguchi-Ikeda M, Kanagawa M, Suzuki T, Miyagoe-Suzuki Y, Toda T, Saito N, Ueyama T. Congenital hearing impairment associated with peripheral cochlear nerve dysmyelination in glycosylation-deficient muscular dystrophy. PLoS Genet. 2020 May 26;16(5):e1008826.

[7]Takahashi H, Kanesaki H, Igarashi T, Kameya S, Yamaki K, Mizota A, Kudo A, Miyagoe-Suzuki Y, Takeda S, Takahashi H. Reactive gliosis of astrocytes and Müller glial cells in retina of POMGnT1-deficient mice. Mol Cell Neurosci. 2011 Jun;47(2):119-30.

[8]Urano F. Wolfram Syndrome: Diagnosis, Management, and Treatment. Curr Diab Rep. 2016 Jan;16(1):6.

[9]Ishihara H, Takeda S, Tamura A, Takahashi R, Yamaguchi S, Takei D, Yamada T, Inoue H, Soga H, Katagiri H, Tanizawa Y, Oka Y. Disruption of the WFS1 gene in mice causes progressive beta-cell loss and impaired stimulus-secretion coupling in insulin secretion. Hum Mol Genet. 2004 Jun 1;13(11):1159-70. 

[10] Ivask M, Volke V, Raasmaja A, Kõks S. High-fat diet associated sensitization to metabolic stress in Wfs1 heterozygous mice. Mol Genet Metab. 2021 Sep-Oct;134(1-2):203-211.

[11] Waszczykowska A, Zmysłowska A, Braun M, Ivask M, Koks S, Jurowski P, Młynarski W. Multiple Retinal Anomalies in Wfs1-Deficient Mice. Diagnostics (Basel). 2020 Aug 19;10(9):607. 

[12] Visnapuu T, Raud S, Loomets M, Reimets R, Sütt S, Luuk H, Plaas M, Kõks S, Volke V, Alttoa A, Harro J, Vasar E. Wfs1-deficient mice display altered function of serotonergic system and increased behavioral response to antidepressants. Front Neurosci. 2013 Jul 31;7:132.

[13] Di Meglio L, Castaldo G, Mosca C, Paonessa A, Gelzo M, Esposito MV, Berni Canani R. Congenital chloride diarrhea clinical features and management: a systematic review. Pediatr Res. 2021 Jul;90(1):23-29.

[14] Schweinfest CW, Spyropoulos DD, Henderson KW, Kim JH, Chapman JM, Barone S, Worrell RT, Wang Z, Soleimani M. slc26a3 (dra)-deficient mice display chloride-losing diarrhea, enhanced colonic proliferation, and distinct up-regulation of ion transporters in the colon. J Biol Chem. 2006 Dec 8;281(49):37962-71.