Chromosomal Microarray Study in Prader-Willi Syndrome

A high-resolution chromosome microarray analysis was performed on 154 consecutive individuals enrolled in the DESTINY PWS clinical trial for Prader-Willi syndrome (PWS). Of these 154 PWS individuals, 87 (56.5%) showed the typical 15q11-q13 deletion subtypes, 62 (40.3%) showed non-deletion maternal disomy 15 and five individuals (3.2%) had separate unexpected microarray findings. For example, one PWS male had Klinefelter syndrome with segmental isodisomy identified in both chromosomes 15 and X. Thirty-five (40.2%) of 87 individuals showed typical larger 15q11-q13 Type I deletion and 52 individuals (59.8%) showed typical smaller Type II deletion. Twenty-four (38.7%) of 62 PWS individuals showed microarray patterns indicating either maternal heterodisomy 15 subclass or a rare non-deletion (epimutation) imprinting center defect. Segmental isodisomy 15 was seen in 34 PWS subjects (54.8%) with 15q26.3, 15q14 and 15q26.1 bands most commonly involved and total isodisomy 15 seen in four individuals (6.5%). In summary, we report on PWS participants consecutively enrolled internationally in a single clinical trial with high-resolution chromosome microarray analysis to determine and describe an unbiased estimate of the frequencies and types of genetic defects and address potential at-risk genetic disorders in those with maternal disomy 15 subclasses in the largest PWS cohort studied to date.

OR10-2 Hormonal and Cardiometabolic Changes Associated with Diazoxide Choline Extended-Release (DCCR) Tablets in Patients with Prader-Willi Syndrome

Background

Prader-Willi syndrome (PWS) is a rare genetic neurodevelopmental condition, characterized by hyperphagia, obesity, hormone deficiencies and behavioral/psychological manifestations. DCCR is under investigation as a treatment for hyperphagia in PWS through its actions on hypothalamic circuits involved in appetite regulation including NPY neurons and central inhibition of DMV neurons to improve insulin sensitivity. In addition to these effects, DCCR acts on pancreatic beta cells, to reduce glucose stimulated insulin secretion, which might have additional effects to reduce fat deposition in adipocytes, serum leptin concentrations and insulin resistance.

Objectives and methods

This analysis characterized changes in hormonal and cardiometabolic parameters in patients with PWS receiving oral daily DCCR. 125 participants with genetically-confirmed PWS ≥4 years old with hyperphagia were treated with DCCR in multi-center studies conducted at 29 sites in the US and the UK: a 13-week, Phase 3, double-blind, placebo-controlled study (DESTINY PWS) and its long-term, open-label extension study (analysis at 52 weeks). The target DCCR dose for these studies was ≥3.3 mg/kg with an optimal dose of 4.2 - 5.8 mg/kg. Overall, 103 patients received DCCR (100-525 mg/day) for 52 weeks. For all parameters, the baseline measurement was defined as (immediately prior to) start of DCCR treatment.

Results

Serum leptin, insulin, and HOMA-IR were significantly reduced following 52 weeks of DCCR administration. Results are expressed as Least square (LS) mean change from baseline [Standard Error (SE)]. There were significant decreases in: Leptin (ng/mL) = -11.08[1.26], p<0.001; Insulin (μIU/mL) = -2.5[0.69], p<0.001; and HOMA-IR = -0.5 [0.17], p=0.003. Serum adiponectin (µg/mL) was significantly increased: 1.82[0.41], p < 0.001. Fat mass measured by DXA was stable at 52 weeks.

Conclusions

The reductions in fasting leptin, insulin and HOMA-IR, and the increase in adiponectin with prolonged DCCR treatment in the absence of reductions in total body fat are consistent with improved insulin sensitivity that may also reflect improvement in leptin sensitivity and healthier body fat distribution, such as reduced visceral adiposity. This could result from both direct pancreatic and hypothalamus-to-periphery actions of DCCR. It remains to be determined if such beneficial metabolic changes also result in reduced systemic inflammation and cardiovascular health.

DCCR administration was associated with significant reductions in leptin, insulin, and HOMA-IR, increases in adiponectin and stabilization of body fat. These and other changes in cardiometabolic parameters suggest that DCCR may have long term health benefit in patients with PWS.

Presentation: Sunday, June 12, 2022 11:15 a.m. - 11:30 a.m.

Prader-Willi syndrome, deletion subtypes, and magnesium: Potential impact on clinical findings

Prader-Willi syndrome is a complex neurodevelopmental genetic imprinting disorder with severe congenital hypotonia, failure to thrive with learning and behavioral problems, and hyperphagia with obesity developing in early childhood. Those with the typical 15q11-q13 Type I deletion compared with the smaller Type II deletion have more severe neurobehavioral problems and differ by the absence of four genes in the 15q11.2 BP1-BP2 region. Two of the genes encode magnesium transporters supporting brain and neurological function and we report on magnesium levels in the two deletion groups of PWS participants. We measured baseline plasma magnesium and analyzed data from a PWS cohort with and without the Type I or Type II deletion. Significantly lower plasma magnesium levels were found in PWS participants with the larger Type I deletion and more so with females with Type I deletion compared with females having the Type II deletion, although magnesium levels remained within normal range in both subgroups. Those with PWS and the larger 15q11-q13 Type I deletion were more clinically affected than those with the smaller Type II deletion. Two of the four genes missing in those with the larger deletion code for magnesium transporters and may impact magnesium levels. Our study showed lower magnesium levels in those with the larger deletion which could contribute to neurobehavioral differences seen in the two separate 15q11-q13 deletion subtypes and in addition affect both glucose and insulin metabolism impacting comorbidities but will require more research.

Evaluation of Methods That Estimate Glomerular Filtration Rate in Patients With Prader-Willi Syndrome

Background: Prader-Willi syndrome (PWS) is a rare, complex, multisystem disorder caused by the loss of multiple paternally expressed genes on chromosome 15q11-13 and is present in 1/15,000-30,000 individuals. Characteristics of PWS include low muscle mass and hypotonia, accumulation of excess body fat, short stature, hyperphagia, behavioral problems, cognitive disabilities, developmental delays, and hypogonadism. In these patients, serum creatinine (SCr)-based methods to calculate estimated glomerular filtration rate (eGFR) can lead to inaccurate results. eGFR is reported to be negatively correlated to muscle mass and PWS-associated low lean body mass may contribute to low SCr levels. Therefore, eGFR calculations may not accurately reflect PWS patient’s renal function. A more accurate, non-invasive, inexpensive means to monitor renal function for this patient population is desirable. Objective: To assess methods of estimating renal function in pediatric PWS patients and summarize the relationship between eGFR and patient-specific factors. Methods: The pre-treatment data of patients ≥4 years old with genetically confirmed PWS participating in an investigational study of DCCR (diazoxide choline) were evaluated. Lean body mass was measured using dual X-ray absorptiometry. Lean body mass and age were correlated to eGFR/creatinine clearance (CrCl) values calculated using four different equations: Bedside Schwartz (BS), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), Modification of Diet in Renal Disease (MDRD), and Cockcroft-Gault (C-G). Results: Of the 124 patients enrolled in the study, 99 were &lt;18 years old and 103 were taking growth hormone (GH). Mean SCr was below normal range at 0.52 mg/dL, with only two subjects (1.6%) having SCr in the normal range (0.84 to 1.21 mg/dL). eGFR calculated using BS was 120±22 mL/min/1.73m2; CKD-EPI 154±23 mL/min/1.73m2; MDRD 211±77 mL/min/1.73m2; and CrCl by C-G 191±80 mL/min. Among the three eGFR equations, CKD-EPI presented with the most reasonable eGFR values &lt;200 mL/min/1.73m2. When stratified by different age groups, SCr increased with age while eGFR decreased (and surprisingly CrCl by C-G increased). When correlating the eGFR values to various parameters, lean mass and age showed significant negative correlations with eGFR for BS, CKD-EPI, and MDRD. In contrast, for C-G there were significant positive correlations between CrCl and both lean mass and age. Conclusion: In PWS, the combination of low SCr and excess accumulation of body fat results in eGFR values that likely overestimate actual renal function in PWS patients. The inconsistent trends in correlation values between eGFR or CrCl by C-G and both lean mass and age indicate current SCr-based methods to estimate renal function in PWS may be inadequate. The use of CKD-EPI or other non-SCr-based methods to monitor renal function should be considered in PWS.

The Potential Role of Activating the ATP-Sensitive Potassium Channel in the Treatment of Hyperphagic Obesity

To evaluate the potential role of ATP-sensitive potassium (K_ATP) channel activation in the treatment of hyperphagic obesity, a PubMed search was conducted focused on the expression of genes encoding the K_ATP channel, the response to activating the K_ATP channel in tissues regulating appetite and the establishment and maintenance of obesity, the evaluation of K_ATP activators in obese hyperphagic animal models, and clinical studies on syndromic obesity. K_ATP channel activation is mechanistically involved in the regulation of appetite in the arcuate nucleus; the regulation of hyperinsulinemia, glycemic control, appetite and satiety in the dorsal motor nucleus of vagus; insulin secretion by β-cells; and the synthesis and β-oxidation of fatty acids in adipocytes. K_ATP channel activators have been evaluated in hyperphagic obese animal models and were shown to reduce hyperphagia, induce fat loss and weight loss in older animals, reduce the accumulation of excess body fat in growing animals, reduce circulating and hepatic lipids, and improve glycemic control. Recent experience with a K_ATP channel activator in Prader-Willi syndrome is consistent with the therapeutic responses observed in animal models. K_ATP channel activation, given the breadth of impact and animal model and clinical results, is a viable target in hyperphagic obesity.

Ribozymes targeted to stearoyl-ACP delta9 desaturase mRNA produce heritable increases of stearic acid in transgenic maize leaves

Ribozymes are RNAs that can be designed to catalyze the specific cleavage or ligation of target RNAs. We have explored the possibility of using ribozymes in maize to downregulate the expression of the stearoyl-acyl carrier protein (Delta9) desaturase gene. Based on site accessibility and catalytic activity, several ribozyme constructs were designed and transformed into regenerable maize lines. One of these constructs, a multimer hammerhead ribozyme linked to a selectable marker gene, was shown to increase leaf stearate in two of 13 maize lines. There were concomitant decreases in Delta9 desaturase mRNA and protein. The plants with the altered stearate phenotype were shown to express ribozyme RNA. The ribozyme-mediated trait was heritable, as evidenced by stearate increases in the leaves of the R1 plants derived from a high-stearate line. The increase in stearate correlated with the presence of the ribozyme gene. A catalytically inactive version of this ribozyme did not produce any significant effect in transgenic maize. This is evidence that ribozymes can be used to modulate the expression of endogenous genes in maize.

The development and ultrastructure of Plasmodium falciparum damaged in vitro by human "crisis" sera and by chloroquine

P. falciparum malaria was cultured in vitro in the presence of sera from patients with cerebral malaria, meningitis and also after chloroquine administration. Intra-erythrocytic parasite damage was seen by light and electron microscopy. The significance of the results is discussed with relevance to non-specific immune mechanisms, and the damage induced by these mechanisms compared with that from chloroquine.

Serotypic variation of culture-adapted isolates of P. falciparum

Culture adapted isolates of P. falciparum had different growth patterns (P less than 0.01) when cultured in the presence of sera obtained from 31 healthy Papua New Guinea residents. Both enhancement and suppression of growth was observed. Less variation was observed using an indirect immunofluorescent antibody method directed against schizont antigens, and no correlation between the two assays was found. This bioassay is assessed as a basis for serotyping P. falciparum strains.

A microassay for detecting merozoite inhibition suitable for routine laboratory use

A micro semiautomative assay of merozoite inhibition antibody has been developed, based on incorporation of radiolabeled isoleucine into parasite protein. The assay has been validated using 44 sera from healthy blood donors in Madang. Inhibition of uptake of label occurred in 43.2% of tests, while an enhancement of uptake was demonstrated in 4.7%. This assay has 'potential' for both seroepidemiological studies, and for providing a mechanism of biotyping wild isolates.