Long term survival of antenatally diagnosed functionally single ventricle congenital heart disease

Funding Acknowledgements

Type of funding sources: None.

Background

Antenatal diagnosis of single ventricle congenital heart disease (CHD) allows prenatal counselling, better parental preparation and support as well as improved perinatal management. Expectant parents frequently ask about likely outcomes and expected longer term survival. Our aim is to review the survival of antenatally diagnosed single ventricle CHD presenting at our institutions between January 2000 and July 2022.

Methods

Retrospective data was collected from the fetal cardiac and paediatric cardiology databases. Maternal data, fetal cardiac diagnosis, postnatal cardiac diagnosis and management were collected for each patient. The outcomes were separated into 2 groups – Cohort 1 (CO1) [2000 to 2007] and Cohort 2 (CO2) [2008 to 2022].

Results

A total of 495 fetuses were diagnosed with single ventricle CHD in the 21 years and 7 months period, with outcomes illustrated in Table 1.

For the small LV group with intention to treat at birth, there was 46% survival at over 10 years for the CO1 group and 69% survival at over 10 years for CO2 group. There was however no significant difference in the survival between the CO1 and CO2 groups (log rank test p=0.12).

For the small RV group with intention to treat at birth, there was 71% survival at over 10 years for the CO1 group and 91% survival at over 10 years for CO2 group. There was significant difference in the survival between the CO1 and CO2 groups (log rank test p=0.03).

No analysis was made for the unspecified hypoplasia as the numbers were too small.

Conclusions

For both the antenatal small LV and small RV groups, the termination rate and compassionate care option remained unchanged between both cohorts.

Overall, there has been improvement in the survival for the antenatal small LV and RV groups with intention to treat. This is likely due to improved perinatal management with detailed management plan and designated delivery at tertiary neonatal hospital close to the cardiac surgical centre, improved surgical expertise and experience, improved cardiac intensive care management as well as availability of ECMO for the sicker patients.

In the antenatal small LV groups, although there has been improvement in survival, this is not yet statistically significant due to more complex patients with more co-morbidity being accepted for surgery.

Whereas for the antenatal small RV groups, we see statistically significant improvement with survival reaching 90% at 10 years, due to increased use of non-surgical intervention like ductal stenting over conventional BT shunts which carry higher morbidity and mortality risk.

Our survival outcomes are comparable with other published data across the world.

Lesch-Nyhan disease causes impaired energy metabolism and reduced developmental potential in midbrain dopaminergic cells

Mutations in HPRT1, a gene encoding a rate-limiting enzyme for purine salvage, cause Lesch-Nyhan disease which is characterized by self-injury and motor impairments. We leveraged stem cell and genetic engineering technologies to model the disease in isogenic and patient-derived forebrain and midbrain cell types. Dopaminergic progenitor cells deficient in HPRT showed decreased intensity of all developmental cell-fate markers measured. Metabolic analyses revealed significant loss of all purine derivatives, except hypoxanthine, and impaired glycolysis and oxidative phosphorylation. real-time glucose tracing demonstrated increased shunting to the pentose phosphate pathway for de novo purine synthesis at the expense of ATP production. Purine depletion in dopaminergic progenitor cells resulted in loss of RHEB, impairing mTORC1 activation. These data demonstrate dopaminergic-specific effects of purine salvage deficiency and unexpectedly reveal that dopaminergic progenitor cells are programmed to a high-energy state prior to higher energy demands of terminally differentiated cells.

Clinical severity in Lesch-Nyhan disease: the role of residual enzyme and compensatory pathways

Mutations in the HPRT1 gene, which encodes the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HGprt), cause Lesch-Nyhan disease (LND) and more mildly affected Lesch-Nyhan variants. Prior studies have suggested a strong correlation between residual hypoxanthine recycling activity and disease severity. However, the relevance of guanine recycling and compensatory changes in the de novo synthesis of purines has received little attention. In the current studies, fibroblast cultures were established for 21 healthy controls and 36 patients with a broad spectrum of disease severity related to HGprt deficiency. We assessed hypoxanthine recycling, guanine recycling, steady-state purine pools, and de novo purine synthesis. There was a strong correlation between disease severity and either hypoxanthine or guanine recycling. Intracellular purines were normal in the HGprt-deficient fibroblasts, but purine wasting was evident as increased purine metabolites excreted from the cells. The normal intracellular purines in the HGprt-deficient fibroblasts were likely due in part to a compensatory increase in purine synthesis, as demonstrated by a significant increase in purinosomes. However, the increase in purine synthesis did not appear to correlate with disease severity. These results refine our understanding of the potential sources of phenotypic heterogeneity in LND and its variants.

Loss of dopamine phenotype among midbrain neurons in Lesch-Nyhan disease

OBJECTIVE

Lesch-Nyhan disease (LND) is caused by congenital deficiency of the purine recycling enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGprt). Affected patients have a peculiar neurobehavioral syndrome linked with reductions of dopamine in the basal ganglia. The purpose of the current studies was to determine the anatomical basis for the reduced dopamine in human brain specimens collected at autopsy.

METHODS

Histopathological studies were conducted using autopsy tissue from 5 LND cases and 6 controls. Specific findings were replicated in brain tissue from an HGprt-deficient knockout mouse using immunoblots, and in a cell model of HGprt deficiency by flow-activated cell sorting (FACS).

RESULTS

Extensive histological studies of the LND brains revealed no signs suggestive of a degenerative process or other consistent abnormalities in any brain region. However, neurons of the substantia nigra from the LND cases showed reduced melanization and reduced immunoreactivity for tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis. In the HGprt-deficient mouse model, immunohistochemical stains for TH revealed no obvious loss of midbrain dopamine neurons, but quantitative immunoblots revealed reduced TH expression in the striatum. Finally, 10 independent HGprt-deficient mouse MN9D neuroblastoma lines showed no signs of impaired viability, but FACS revealed significantly reduced TH immunoreactivity compared to the control parent line.

INTERPRETATION

These results reveal an unusual phenomenon in which the neurochemical phenotype of dopaminergic neurons is not linked with a degenerative process. They suggest an important relationship between purine recycling pathways and the neurochemical integrity of the dopaminergic phenotype.

Purine metabolism during neuronal differentiation: the relevance of purine synthesis and recycling

Purines are a class of small organic molecules that are essential for all cells. They play critical roles in neuronal differentiation and function. Their importance is highlighted by several inherited disorders of purine metabolism, such as Lesch-Nyhan disease, which is caused by a deficiency of the purine salvage enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGprt). Despite the known importance of purines in the nervous system, knowledge regarding their metabolism in neurons is limited. In the current studies, purine pools and their metabolism were examined in rat PC6-3 cells, a PC12 pheochromocytoma subclone that undergoes robust differentiation with nerve growth factor. The results were compared with five new independent PC6-3 subclones with defective purine recycling because of different mutations affecting HGprt enzyme activity. The results demonstrate an increase in most purines and in energy state following neuronal differentiation, as well as specific abnormalities when purine recycling is lost. The loss of HGprt-mediated purine recycling also is associated with significant loss of dopamine and related metabolites in the mutant PC6-3 lines, suggesting an important connection between purine and dopamine pathways. These results provide insights into how purine pools and metabolism change with neuronal differentiation, and how specific enzyme defects may cause neuronal dysfunction. Differentiation of dopaminergic PC6-3 cells is accompanied by increased purine pools and energy state. The lack of a functional purine recycling pathway causes purine limitation in both undifferentiated and differentiated cells, as well as profound loss of dopamine content. The results imply an unknown mechanism by which intracellular purine levels regulate dopamine levels.

Bone marrow mobilization with granulocyte macrophage colony-stimulating factor improves endothelial dysfunction and exercise capacity in patients with peripheral arterial disease

BACKGROUND

We hypothesized that granulocyte macrophage colony-stimulating factor (GM-CSF) administration will be safe and will improve endothelial dysfunction and exercise capacity by mobilizing progenitor cells in patients with peripheral arterial disease (PAD).

METHODS

Forty-five patients with PAD received thrice-weekly injections for 2 weeks of 3, 6, or 10 microg/kg per day of GM-CSF or placebo in successive cohorts of 15 subjects randomized 2:1 to drug or placebo. CD34+ mononuclear cell subsets and colony formation assay, endothelial function, ankle-brachial index, and walking capacity were measured.

RESULTS

Granulocyte macrophage colony-stimulating factor administration was safe. After pooling data from GM-CSF cohorts, at 2 weeks, there was a significant increase in total leukocytes (43%, P < .0001), CD34+ cells (46%, P = .035), and colony-forming units (31%, P = .026, week 1). At 12 weeks, endothelial function improved with GM-CSF (flow-mediated vasodilation increased by 59%, P < .01) as did pain-free treadmill walking time (38 seconds, P = .008) and total treadmill walking time (55 seconds, P = .016). Corresponding changes were not observed in the placebo group.

CONCLUSIONS

Granulocyte macrophage colony-stimulating factor therapy in patients with PAD was associated with mobilization of progenitor cells, improvement of endothelial dysfunction, and exercise capacity. The efficacy of strategies designed to mobilize bone marrow progenitors warrants further study in patients with PAD.

The effects of maternal hyperphenylalaninemia on learning in mature rats

Pregnant rats were given a diet supplemented with 0.5% alpha-methyl-phenylalanine and 3% phenylalanine from the 12th day of gestation to term. Compared to unsupplemented controls, maternal serum phenylalanine was elevated 8-10-fold. Experimental litters did not differ from controls in number of offspring, birth weight, or subsequent growth on an unsupplemented diet. At 8 weeks of age, animals were tested for latent learning on a 4-arm maze, and at 10 weeks, they were tested for observational learning with littermates in a food preference paradigm. In both tests, experimental animals did learn, but significantly less than controls. The data suggest that maternal hyperphenylalaninemia, induced as a model for the inborn error, phenylketonuria, can lead to learning deficits later in the lives of offspring.