Jennifer L. Miller

The Dendritic Cell Lineage: Ontogeny and Function of Dendritic Cells and Their Subsets in the Steady State and the Inflamed Setting

Dendritic cells (DCs) form a remarkable cellular network that shapes adaptive immune responses according to peripheral cues. After four decades of research, we now know that DCs arise from a hematopoietic lineage distinct from other leukocytes, establishing the DC system as a unique hematopoietic branch. Recent work has also established that tissue DCs consist of developmentally and functionally distinct subsets that differentially regulate T lymphocyte function. This review discusses major advances in our understanding of the regulation of DC lineage commitment, differentiation, diversification, and function in situ.

Prader-Willi syndrome

Prader-Willi syndrome is characterized by severe infantile hypotonia with poor suck and failure to thrive; hypogonadism causing genital hypoplasia and pubertal insufficiency; characteristic facial features; early-childhood onset obesity and hyperphagia; developmental delay/mild intellectual disability; short stature; and a distinctive behavioral phenotype. Sleep abnormalities and scoliosis are common. Growth hormone insufficiency is frequent, and replacement therapy provides improvement in growth, body composition, and physical attributes. Management is otherwise largely supportive. Consensus clinical diagnostic criteria exist, but diagnosis should be confirmed through genetic testing. Prader-Willi syndrome is due to absence of paternally expressed imprinted genes at 15q11.2-q13 through paternal deletion of this region (65–75% of individuals), maternal uniparental disomy 15 (20–30%), or an imprinting defect (1–3%). Parent-specific DNA methylation analysis will detect >99% of individuals. However, additional genetic studies are necessary to identify the molecular class. There are multiple imprinted genes in this region, the loss of which contribute to the complete phenotype of Prader-Willi syndrome. However, absence of a small nucleolar organizing RNA gene, SNORD116, seems to reproduce many of the clinical features. Sibling recurrence risk is typically <1%, but higher risks may pertain in certain cases. Prenatal diagnosis is available.Genet Med 2012:14(1):10–26.

Specialized role of migratory dendritic cells in peripheral tolerance induction

Harnessing DCs for immunotherapies in vivo requires the elucidation of the physiological role of distinct DC populations. Migratory DCs traffic from peripheral tissues to draining lymph nodes charged with tissue self antigens. We hypothesized that these DC populations have a specialized role in the maintenance of peripheral tolerance, specifically, to generate suppressive Foxp3+ Tregs. To examine the differential capacity of migratory DCs versus blood-derived lymphoid-resident DCs for Treg generation in vivo, we targeted a self antigen, myelin oligodendrocyte glycoprotein, using antibodies against cell surface receptors differentially expressed in these DC populations. Using this approach together with mouse models that lack specific DC populations, we found that migratory DCs have a superior ability to generate Tregs in vivo, which in turn drastically improve the outcome of experimental autoimmune encephalomyelitis. These results provide a rationale for the development of novel therapies targeting migratory DCs for the treatment of autoimmune diseases.

Nutritional Phases in Prader–Willi Syndrome

Prader–Willi syndrome (PWS) is a complex neurobehavioral condition which has been classically described as having two nutritional stages: poor feeding, frequently with failure to thrive (FTT) in infancy (Stage 1), followed by hyperphagia leading to obesity in later childhood (Stage 2). We have longitudinally followed the feeding behaviors of individuals with PWS and found a much more gradual and complex progression of the nutritional phases than the traditional two stages described in the literature. Therefore, this study characterizes the growth, metabolic, and laboratory changes associated with the various nutritional phases of PWS in a large cohort of subjects. We have identified a total of seven different nutritional phases, with five main phases and sub‐phases in phases 1 and 2. Phase 0 occurs in utero, with decreased fetal movements and growth restriction compared to unaffected siblings. In phase 1 the infant is hypotonic and not obese, with sub‐phase 1a characterized by difficulty feeding with or without FTT (ages birth—15 months; median age at completion: 9 months). This phase is followed by sub‐phase 1b when the infant grows steadily along a growth curve and weight is increasing at a normal rate (median age of onset: 9 months; age quartiles 5–15 months). Phase 2 is associated with weight gain—in sub‐phase 2a the weight increases without a significant change in appetite or caloric intake (median age of onset 2.08 years; age quartiles 20–31 months;), while in sub‐phase 2b the weight gain is associated with a concomitant increased interest in food (median age of onset: 4.5 years; quartiles 3–5.25 years). Phase 3 is characterized by hyperphagia, typically accompanied by food‐seeking and lack of satiety (median age of onset: 8 years; quartiles 5–13 years). Some adults progress to phase 4 which is when an individual who was previously in phase 3 no longer has an insatiable appetite and is able to feel full. Therefore, the progression of the nutritional phases in PWS is much more complex than previously recognized. Awareness of the various phases will aid researchers in unraveling the pathophysiology of each phase and provide a foundation for developing rational therapies. Counseling parents of newly diagnosed infants with PWS as to what to expect with regard to these nutritional phases may help prevent or slow the early‐onset of obesity in this syndrome.

Growth Hormone Research Society Workshop Summary: Consensus Guidelines for Recombinant Human Growth Hormone Therapy in Prader-Willi Syndrome

Context: Recombinant human GH (rhGH) therapy in Prader-Willi syndrome (PWS) has been used by the medical community and advocated by parental support groups since its approval in the United States in 2000 and in Europe in 2001. Its use in PWS represents a unique therapeutic challenge that includes treating individuals with cognitive disability, varied therapeutic goals that are not focused exclusively on increased height, and concerns about potential life-threatening adverse events. Objective: The aim of the study was to formulate recommendations for the use of rhGH in children and adult patients with PWS. Evidence: We performed a systematic review of the clinical evidence in the pediatric population, including randomized controlled trials, comparative observational studies, and long-term studies (>3.5 y). Adult studies included randomized controlled trials of rhGH treatment for ≥ 6 months and uncontrolled trials. Safety data were obtained from case reports, clinical trials, and pharmaceutical registries. Methodology: Forty-three international experts and stakeholders followed clinical practice guideline development recommendations outlined by the AGREE Collaboration (www.agreetrust.org). Evidence was synthesized and graded using a comprehensive multicriteria methodology (EVIDEM) (http://bit.ly.PWGHIN). Conclusions: Following a multidisciplinary evaluation, preferably by experts, rhGH treatment should be considered for patients with genetically confirmed PWS in conjunction with dietary, environmental, and lifestyle interventions. Cognitive impairment should not be a barrier to treatment, and informed consent/assent should include benefit/risk information. Exclusion criteria should include severe obesity, uncontrolled diabetes mellitus, untreated severe obstructive sleep apnea, active cancer, or psychosis. Clinical outcome priorities should vary depending upon age and the presence of physical, mental, and social disability, and treatment should be continued for as long as demonstrated benefits outweigh the risks.

Enhanced activation of reward mediating prefrontal regions in response to food stimuli in Prader–Willi syndrome

Background: Individuals with Prader–Willi syndrome (PWS) exhibit severe disturbances in appetite regulation, including delayed meal termination, early return of hunger after a meal, seeking and hoarding food and eating of non-food substances. Brain pathways involved in the control of appetite in humans are thought to include the hypothalamus, frontal cortex (including the orbitofrontal, ventromedial prefrontal, dorsolateral prefrontal and anterior cingulate areas), insula, and limbic and paralimbic areas. We hypothesised that the abnormal appetite in PWS results from aberrant reward processing of food stimuli in these neural pathways. Methods: We compared functional MRI blood oxygen level dependent (BOLD) responses while viewing pictures of food in eight adults with PWS and eight normal weight adults after ingestion of an oral glucose load. Results: Subjects with PWS demonstrated significantly greater BOLD activation in the ventromedial prefrontal cortex than controls when viewing food pictures. No significant differences were found in serum insulin, glucose or triglyceride levels between the groups at the time of the scan. Conclusions: Individuals with PWS had an increased BOLD response in the ventromedial prefrontal cortex compared with normal weight controls when viewing pictures of food after an oral glucose load. These findings suggest that an increased reward value for food may underlie the excessive hunger in PWS, and support the significance of the frontal cortex in modulating the response to food in humans. Our findings in the extreme appetite phenotype of PWS support the importance of the neural pathways that guide reward related behaviour in modulating the response to food in humans.

Intracranial abnormalities detected by three-dimensional magnetic resonance imaging in Prader–Willi syndrome†

The neuropathologic abnormalities associated with Prader–Willi syndrome (PWS) are largely unknown. PWS is due to the loss of several paternally expressed genes in chromosome 15q11‐q13 region. Several of the imprinted genes in the 15q11‐q13 region are normally expressed in the brain and thought to be necessary for neuronal growth and development. Thus, we hypothesized that we would find abnormalities in gray and white matter growth in individuals with PWS. We evaluated three‐dimensional (3‐D) MRI scans of 20 individuals with PWS, aged three months to 39 years, and compared them to 3‐D MRI scans of 21 normal weight sibling controls and 16 individuals with early‐onset morbid obesity (EMO) of unknown etiology. The interpreters of the scans were blinded to the diagnosis of the subjects. Intracranial abnormalities in individuals with PWS included ventriculomegaly (100% of individuals), decreased volume of brain tissue in the parietal‐occipital lobe (50%), sylvian fissure polymicrogyria (60%), and incomplete insular closure (65%). None of the EMO or normal weight control subjects had any of these findings. We found multiple morphologic brain abnormalities in subjects with PWS suggesting that the loss of paternally expressed genes in chromosome 15q11‐q13 region may result in abnormalities of neuronal development. The specific mechanisms underlying these neuropathological abnormalities and their correlation with the clinical phenotype remain to be elucidated.

Unique and atypical deletions in Prader–Willi syndrome reveal distinct phenotypes

Prader–Willi syndrome (PWS) is a multisystem, contiguous gene disorder caused by an absence of paternally expressed genes within the 15q11.2-q13 region via one of the three main genetic mechanisms: deletion of the paternally inherited 15q11.2-q13 region, maternal uniparental disomy and imprinting defect. The deletion class is typically subdivided into Type 1 and Type 2 based on their proximal breakpoints (BP1–BP3 and BP2–BP3, respectively). Despite PWS being a well-characterized genetic disorder the role of the specific genes contributing to various aspects of the phenotype are not well understood. Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) is a recently developed technique that detects copy number changes and aberrant DNA methylation. In this study, we initially applied MS-MLPA to elucidate the deletion subtypes of 88 subjects. In our cohort, 32 had a Type 1 and 49 had a Type 2 deletion. The remaining seven subjects had unique or atypical deletions that were either smaller (n=5) or larger (n=2) than typically described and were further characterized by array-based comparative genome hybridization. In two subjects both the PWS region (15q11.2) and the newly described 15q13.3 microdeletion syndrome region were deleted. The subjects with a unique or an atypical deletion revealed distinct phenotypic features. In conclusion, unique or atypical deletions were found in ∼8% of the deletion subjects with PWS in our cohort. These novel deletions provide further insight into the potential role of several of the genes within the 15q11.2 and the 15q13.3 regions.

Pituitary abnormalities in Prader–Willi syndrome and early onset morbid obesity†

Prader–Willi syndrome (PWS) is a well‐defined syndrome of childhood‐obesity which can serve as a model for investigating early onset childhood obesity. Many of the clinical features of PWS (e.g., hyperphagia, hypogonadotropic hypogonadism, growth hormone deficiency) are hypothesized to be due to abnormalities of the hypothalamus and/or pituitary gland. Children who become severely obese very early in life (i.e., before age 4 years) may also have a genetic etiology of their obesity, perhaps with associated neuroendocrine and hypothalamo‐pituitary defects, as infants and very young children have limited access to environmental factors that contribute to obesity. We hypothesized that morphologic abnormalities of the pituitary gland would be seen in both individuals with PWS and other subjects with early onset morbid obesity (EMO). This case‐control study included individuals with PWS (n = 27, age 3 months to 39 years), patients with EMO of unknown etiology (n = 16, age 4–22 years; defined as body mass index greater than the 97th centile for age before age 4 years), and normal weight siblings (n = 25, age 7 months to 43 years) from both groups. Participants had 3‐dimensional magnetic resonance imaging to evaluate the pituitary gland, a complete history and physical examination, and measurement of basal pituitary hormones. Subjects with PWS and EMO had a higher prevalence of pituitary morphological abnormalities than did control subjects (74% PWS, 69% EMO, 8% controls; P < 0.001). Anterior pituitary hormone deficiencies were universal in individuals with PWS (low IGF‐1 in 100%, P < 0.001 PWS vs. controls; central hypothyroidism in 19%, P = 0.052, and hypoplastic genitalia or hypogonadotropic hypogonadism in 100%, P < 0.001), and was often seen in individuals with EMO (6%, P = 0.89 vs. control, 31%, P = 0.002, and 25%, P = 0.018, respectively). The presence of a hypoplastic pituitary gland appeared to correlate with the presence of anterior pituitary hormone deficiencies in individuals with EMO, but no correlation was apparent in individuals with PWS. In conclusion, the high frequency of both morphological and hormonal abnormalities of the pituitary gland in both individuals with PWS and EMO suggests that abnormalities in the hypothalamo‐pituitary axis are features not only of PWS, but also frequently of EMO of unknown etiology.

Management approaches for pediatric obesity

Childhood obesity is a worldwide problem that has reached epidemic proportions, resulting in an increased prevalence of premature obesity-related morbidities, and, thus, probable increased health-care costs to treat children. The development of viable approaches to manage this epidemic is crucial. Most experts in the field of childhood obesity agree that the prevention of obesity in children should be the first line of management. Pediatricians must be adept at recognizing children at risk of obesity, calculating and plotting the BMI at all visits, using a change in the BMI to identify excessive weight gain, and monitoring for comorbidities associated with obesity. If obesity is present, the cornerstone of treatment is modification of dietary and exercise habits. Practice-based counseling and community-based programs that support and encourage lifestyle modifications have yielded promising short-term results. Children with severe comorbidities who are unable to achieve lifestyle modifications can be considered for either pharmacologic therapy or surgery, but these options should be considered as a last resort. Early intervention and prevention strategies are the most cost-effective methods of dealing with this issue.