Combined deficiency of alpha and epsilon sarcoglycan disrupts the cardiac dystrophin complex.

Cardiomyopathy is a puzzling complication in addition to skeletal muscle pathology for patients with mutations in ß-, γ- or δ-sarcoglycan (SG) genes. Patients with mutations in α-SG rarely have associated cardiomyopathy, or their cardiac pathology is very mild. We hypothesize that a fifth SG, ε-SG, may compensate for α-SG deficiency in the heart. To investigate the function of ε-SG in striated muscle, we generated an Sgce-null mouse and a Sgca-;Sgce-null mouse, which lacks both α- and ε-SGs. While Sgce-null mice showed a wild-type phenotype, with no signs of muscular dystrophy or heart disease, the Sgca-;Sgce-null mouse developed a progressive muscular dystrophy and a more anticipated and severe cardiomyopathy. It shows a complete loss of residual SGs and a strong reduction in both dystrophin and dystroglycan. Our data indicate that ε-SG is important in preventing cardiomyopathy in α-SG deficiency.

Lack of Mid1, the mouse ortholog of the Opitz syndrome gene, causes abnormal development of the anterior cerebellar vermis.

Opitz G/BBB syndrome (OS) is a genetic disorder characterized by midline developmental defects. Male patients with the X-linked form of OS, caused by loss-of-function mutations in the MID1 gene, show high variability of the clinical signs. MID1 encodes a ubiquitin ligase that controls phosphatase 2A, but its role in the pathogenesis of the disease is still unclear. Here, we report a mouse line carrying a nonfunctional ortholog of the human MID1 gene, Mid1. Mid1-null mice show the brain anatomical defect observed in patients (i.e., hypoplasia of the anterior portion of the medial cerebellum, the vermis). We found that the presence of this defect correlates with motor coordination and procedural and nonassociative learning impairments. The defect is limited to the most anterior lobes of the vermis, the region of the developing cerebellum adjacent to the dorsal midbrain. Analyses at midgestation reveal that lack of Mid1 causes the shortening of the posterior dorsal midbrain, the rostralization of the midbrain/cerebellum boundary, and the downregulation of a key player in the development of this region, Fgf17. Thus, lack of Mid1 causes a misspecification of the midbrain/cerebellar boundary that results in an abnormal development of the most anterior cerebellar lobes. This animal model provides a tool for additional in vivo studies of the physiological and pathological role of the Mid1 gene and a system to investigate the development and function of anterior cerebellar domains.

Use of a lower dosage liver-detargeted AAV vector to prevent hamster muscular dystrophy.

The BIO14.6 hamster carries a mutation in the delta sarcoglycan gene causing muscular dystrophy and cardiomyopathy. The disease can be prevented by systemic delivery of delta sarcoglycan cDNA using adeno-associated viruses (AAVs). However, all AAVs also target the liver, raising concerns about their therapeutic efficacy in human applications. We compared the AAV2/8 with the chimeric AAV2/2i8, in which the 585-QQNTAP-590 motif of the AAV8 serotype was added to the heparan sulfate receptor footprint of the AAV2 strain. Both vectors carrying the human delta sarcoglycan cDNA were delivered into 24 14-day-old BIO14.6 hamsters. We followed transgene expression in muscle and liver for 7 months. We detected a sustained ectopic expression of delta sarcoglycan in the liver when using AAV2/8 but not AAV2/2i8. Genomic copies of AAV2/2i8 were not detectable in the liver, while at least 100-fold more copies of AAV2/8 were counted. In contrast, the hamster skeletal muscle expressed more delta sarcoglycan using AAV2/2i8 and were still healthy after 7 months at the lower dosage. We conclude that this chimeric vector is a robust option for safer and longer-term diseased muscle targeting.

Worsening of cardiomyopathy using deflazacort in an animal model rescued by gene therapy.

We have previously demonstrated that gene therapy can rescue the phenotype and extend lifespan in the delta-sarcoglycan deficient cardiomyopathic hamster. In patients with similar genetic defects, steroids have been largely used to slow down disease progression. Aim of our study was to evaluate the combined effects of steroid treatment and gene therapy on cardiac function. We injected the human delta-sarcoglycan cDNA by adeno-associated virus (AAV) 2/8 by a single intraperitoneal injection into BIO14.6 Syrian hamsters at ten days of age to rescue the phenotype. We then treated the hamsters with deflazacort. Treatment was administered to half of the hamsters that had received the AAV and the other hamsters without AAV, as well as to normal hamsters. Both horizontal and vertical activities were greatly enhanced by deflazacort in all groups. As in previous experiments, the AAV treatment alone was able to preserve the ejection fraction (70±7% EF). However, the EF value declined (52±14%) with a combination of AAV and deflazacort. This was similar with all the other groups of affected animals. We confirm that gene therapy improves cardiac function in the BIO14.6 hamsters. Our results suggest that deflazacort is ineffective and may also have a negative impact on the cardiomyopathy rescue, possibly by boosting motor activity. This is unexpected and may have significance in terms of the lifestyle recommendations for patients.