The new biology enters the generalist pediatrician's office: lessons from the Human Genome Project.

American College of Medical Genetics Statement on Diagnostic Testing for Uniparental Disomy

Epilepsy in Angelman syndrome

Screening of Prader-Willi syndrome and Angelman syndrome in school children with moderate to profound mental retardation in southern Taiwan.

Prader-Willi and Angelman syndromes are 2 clinically distinct disorders associated with multiple anomalies and mental retardation. They are only discussed together because they share a similar and uncommon genetic basis: they involve genes that are located in the same region in the genome and are characterized by genetic imprinting. This normal process has contributed to these 2 complex and severe conditions through inactivation of 1 copy of the genes relevant to each disorder: the maternally derived copy of genes for Prader-Willi syndrome in proximal 15q are normally silent, and a paternally derived copy of 1 gene for Angelman syndrome in 15q is normally silent. For both disorders, when the normally active copy of the gene or genes is missing, abnormality results. Since the genes for these 2 disorders are located very close together, and since the center involved in inactivating the genes involved in imprinting may be the same, both these disorders usually result from the same chromosomal deletion; which disorder results depends on the parent of origin of the chromosome 15 that becomes deleted. Both Prader-Willi and Angelman syndrome can also occur as a result of having both members of the chromosome 15 pair derived from 1 parent, a condition known as uniparental disomy. Both can also result from a structural abnormality of the imprinting center, known as an imprinting mutation. In addition, Angelman syndrome can be caused by a mutation in the gene that causes it; a comparable cause is not present in Prader-Willi syndrome since it results from abnormality in more than 1 gene. Finally, despite the complexity of possible causes, all but the single gene mutation of the Angelman syndrome gene can be detected through methylation-sensitive DNA probes, since DNA methylation is the process by which the genes for these 2 disorders are imprinted. This unusual property of specific areas of the DNA holds promise for future treatment of these and other disorders related to imprinting through reversal of the imprinting process.

Ornithine carbamoyltransferase (OTC) is a key enzyme in the urea cycle to detoxify ammonium produced from amino acid catabolism. OTC deficiency is an X-linked genetic disorder ranging from fatal in newborns to hyperammonemia and anorexia in adults. Through affinity purification of acetylated peptides and mass spectrometry, we identified that OTC is acetylated on lysine residues, including Lys88, which is also mutated in OTC-deficient patients. OTC acetylation was confirmed to occur under physiological conditions. Biochemical characterizations revealed that OTC Lys88 acetylation decreases the affinity for carbamoyl phosphate, one of the two OTC substrates, and the maximum velocity, whereas the K(m) for ornithine, the other OTC substrate, is not affected. Furthermore, Lys88 acetylation is regulated by both extracellular glucose and amino acid availability, indicating that OTC activity may be regulated by cellular metabolic status. Our results provide an example of the novel mechanism of regulating metabolic enzyme activity through protein acetylation.

The Sins of the Fathers and Mothers: Genomic Imprinting in Mammalian Development

Most cases of Prader-Willi syndrome are caused by partial deletion of the paternally derived chromosome 15, while maternally derived chromosome 15 is responsible for Angelman syndrome. We report the results of molecular and cytogenetic analyses of a patient who was given a final diagnosis of Prader-Willi syndrome, but also had manifestations consistent with Angelman syndrome. The patient was a 15-year-old boy. After birth, PraderWilli syndrome was diagnosedon fluorescence in situ hybridization (FISH), performed because of muscular hypotonia, failure to thrive, and bilateral cryptorchidism. However, at the age of 2 years, the diagnosis was revised to Angelman syndrome because of atypical absence, characteristic electroencephalographic discharges, mental retardation, and excessive laughter. At the age of 14 years, type 2 diabetes developed, and he is now receivinginsulin glargine and voglibose. The height is 147.0 cm (-3.68 SD), and the body weight is 55.0 kg (body mass index, 25.5 kg/m 2 ). He cannot speak any meaningful words or walk. He has hyperphagia, hypopigmentation, almond-shaped eyes, small hands and feet, and a large mouth and jaw. Chromosomal examination by G-banding stain revealed that the karyotype was a mosaic composed of 45, XY, der(1) t(1;15)(p36.3; q13), -15 and 46, XY, der(1) t(1;15) (p36.3; q13),-15 ,+mar. FISH did not detect signals of UBE3A/D15S10 with the probe for Angelman syndrome or SNRPN for Prader-Willi syndrome on the der(1) chromosome. The marker chromosome was derived from the short arm of chromosome 15. Methylation-specific PCR amplified the SNRPN gene using only primers specific for methylated gene. FISH for 1p36 deletion syndrome did not detect the deletion on the der(1) chromosome. We concluded that his diagnosis was Prader-Willi syndrome caused by the partial deletion of the long arm of chromosome 15, which had translocated onto chromosome 1. The clinical manifestations might have beenmodified by the complicatedstructural changes in chromosomesas well as by possible terminal deletion of the short arm of chromosome 1, which could not be detected on FISH.

Back to table of contents Previous article Next article Images in NeuroscienceFull AccessThe Human Genome: Detecting Chromosomal Deletions: Angelman and Prader-Willi SyndromesDeborah J. Morris-Rosendahl, PH.D., and Eike Back, M.D., Deborah J. Morris-RosendahlSearch for more papers by this author, PH.D., and Eike BackSearch for more papers by this author, M.D., Frieburg, GermanyPublished Online:1 Mar 2002https://doi.org/10.1176/appi.ajp.159.3.372AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail Angelman syndrome and Prader-Willi syndrome are two related but clinically and genetically distinct neurogenetic syndromes, characteristically caused by deletion of the human chromosomal region 15q11-q13. Clinical features of Angelman syndrome include severe mental retardation with absence of speech, epileptic seizures, ataxia, inappropriate bursts of laughter, unusually happy disposition, hyperactivity, and micro- and brachycephaly. Patients with Prader-Willi syndrome show infantile hypotonia, mild to moderate mental retardation, hyperphagia with subsequent obesity, hypogonadism, short stature, mild facial dysmorphism, and characteristic behavior. In Angelman syndrome the chromosomal deletions are exclusively of the maternal chromosome, whereas in Prader-Willi syndrome the deletions are of paternal origin, i.e., the absence of any paternal contribution to the 15q11-q13 region. Both syndromes can result either from deletions or from uniparental disomy, in which two chromosomes 15 are inherited from a single parent, instead of one chromosome from each parent.The detection of chromosomal deletions has become routine in both prenatal and postnatal diagnosis with the use of fluorescence in situ hybridization, a process that vividly paints chromosomes or portions of chromosomes with fluorescent molecules. In situ hybridization is a powerful and versatile tool for the detection and localization of nucleic acid sequences (the constituents of genes) in cell preparations. The technique is based on the hybridization (attraction and complexing) of a labeled and complementary DNA or RNA probe to immobilized chromosomal preparations. Although radioactively labeled DNA probes were formerly used for this purpose, commercially available fluorescent probes are now available for diagnosis. Fluorescence in situ hybridization is routinely used to detect chromosomal rearrangements and deletions, including those associated with chromosomal microdeletion syndromes, such as Angelman syndrome or Prader-Willi syndrome.Address reprint requests to Dr. Tamminga, Maryland Psychiatric Research Center, University of Maryland, P.O. Box 21247, Baltimore, MD 21228; [email protected] (e-mail). Image courtesy of the authors. FigureFluorescence in situ hybridization image showing the deletion of chromosomal region 15q11-q13 that causes Angelman syndrome. Two control probes—CEP 15 and LSI PML (Vysis, Downers Grove, Ill.)—are included in the probe mixture to highlight the short arms around the centromeric region (CEP 15 on 15p11.2, blue-green signals) and long arms (LSI PML on 15q22, orange-pink signals) of chromosome 15 and to detect possible chromosomal translocations. The absence of one of the orange-pink signals on one chromosome 15 (q11-q13, white arrow) indicates the deletion of the small nuclear ribonucleoprotein-associated polypeptide N locus in this 3-year-old male Angelman syndrome patient. FiguresReferencesCited byDetailsCited byNone Volume 159Issue 3 March 2002Pages 372-372 Metrics PDF download History Published online 1 March 2002 Published in print 1 March 2002

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are two distinct neurogenetic disorders in which imprinted genes on the proximal long arm of chromosome 15 are affected. Although the SNORD116 gene cluster has become a prime candidate for PWS, it cannot be excluded that other paternally expressed genes in the chromosomal region 15q11q13 contribute to the full phenotype. AS is caused by a deficiency of the UBE3A gene, which in the brain is expressed from the maternal allele only. The most frequent genetic lesions in both disorders are a de novo deletion of the chromosomal region 15q11q13, uniparental disomy 15, an imprinting defect or, in the case of AS, a mutation of the UBE3A gene. Microdeletions in a small number of patients with PWS and AS have led to the identification of the chromosome 15 imprinting center (IC). The IC consists of two critical elements, which act in cis to regulate imprinting in the whole chromosome 15q11q13 imprinted domain.

Chapter 14 - Gene therapy: advocacies, perspectives, and ethical provocations

Prader–Willi and Angelman syndromes are often referred to as a sister pair of neurodevelopmental disorders, resulting from different genetic and epigenetic alterations to the same chromosomal region, 15q11-q13. Some of the primary phenotypes of the two syndromes have been suggested to be opposite to one another, but this hypothesis has yet to be tested comprehensively, and it remains unclear how opposite effects could be produced by changes to different genes in one syndrome compared to the other. We evaluated the evidence for opposite effects on sleep and eating phenotypes in Prader–Willi syndrome and Angelman syndrome, and developed physiological–genetic models that represent hypothesized causes of these differences. Sleep latency shows opposite deviations from controls in Prader–Willi and Angelman syndromes, with shorter latency in Prader–Willi syndrome by meta-analysis and longer latency in Angelman syndrome from previous studies. These differences can be accounted for by the effects of variable gene dosages of UBE3A and MAGEL2, interacting with clock genes, and leading to acceleration (in Prader–Willi syndrome) or deceleration (in Angelman syndrome) of circadian rhythms. Prader–Willi and Angelman syndromes also show evidence of opposite alterations in hyperphagic food selectivity, with more paternally biased subtypes of Angelman syndrome apparently involving increased preference for complementary foods (“baby foods”); hedonic reward from eating may also be increased in Angelman syndrome and decreased in Prader–Willi syndrome. These differences can be explained in part under a model whereby hyperphagia and food selectivity are mediated by the effects of the genes SNORD-116, UBE3A and MAGEL2, with outcomes depending upon the genotypic cause of Angelman syndrome. The diametric variation observed in sleep and eating phenotypes in Prader–Willi and Angelman syndromes is consistent with predictions from the kinship theory of imprinting, reflecting extremes of higher resource demand in Angelman syndrome and lower demand in Prader–Willi syndrome, with a special emphasis on social–attentional demands and attachment associated with bedtime, and feeding demands associated with mother-provided complementary foods compared to offspring-foraged family-type foods.

Although individually inborn errors of metabolism are rare, collectively they contribute significantly to morbidity and mortality in the pediatric age group. There are several reasons why, out of these inborn errors of metabolism, urea cycle disorders have emerged as potentially good candidates for the development of gene therapy. Studies have initially focused on ornithine carbamoyltransferase (OCT) deficiency in part because there are mouse models of this disease and in part because this disease is particularly resistant to current therapies. Both in vivo and ex vivo approaches to gene therapy are being developed for the treatment of urea cycle disorders. Ex vivo gene therapy is appealing because of the long‐term expression that can be achieved, but there are clear limitations to this approach. In vivo gene therapy using adenoviral vectors is attractive for several reasons, including the fact that the virus can be administered by intravenous injection, the high levels of expression observed after a single injection, and the rapidity of that expression. Studies of transgene expression in the mouse models of OCT deficiency (OCTD) have been encouraging, but have also provided evidence that the immune system may be involved in mediating two limiting aspects of this technology, transient gene expression and inflammation. Although deletions in adenoviral early genes should limit adenoviral late gene expression and subsequent viral replication, there is in vitro and in vivo evidence of late gene expression after infection with adenoviruses deleted of some of the early genes. Future studies will focus on systematically defining the components of the virus that are recognized by the immune system and mutating these gene products. The development of an approach to gene therapy that safely, stably, and efficiently transduces gene expression holds the promise of revolutionizing the treatment of inborn errors of urea synthesis. © 1995 Wiley‐Liss, Inc.

Recent studies have identified a new class of Prader-Willi syndrome (PWS) and Angelman syndrome (AS) patients who have biparental inheritance, but neither the typical deletion nor uniparental disomy (UPD) or translocation. However, these patients have uniparental DNA methylation throughout 15q11-q13, and thus appear to have a mutation in the imprinting process for this region. Here we describe detailed clinical findings of five AS imprinting mutation patients (three families) and two PWS imprinting mutation patients (one new family). All these patients have essentially the classical clinical phenotype for the respective syndrome, except that the incidence of microcephaly is lower in imprinting mutation AS patients than in deletion AS patients. Furthermore, imprinting mutation AS and PWS patients do not typically have hypopigmentation, which is commonly found in patients with the usual large deletion. Molecular diagnosis of these cases is initially achieved by DNA methylation analyses of the DN34/ZNF127, PW71 (D15S63), and SNRPN loci. The latter two probes have clear advantages in the simple molecular diagnostic analysis of PWS and AS patients with an imprinting mutation, as has been found for typical deletion or UPD PWS and AS cases. With the recent finding of inherited microdeletions in PWS and AS imprinting mutation families, our studies define a new class of these two syndromes. The clinical and molecular identification of these PWS and AS patients has important genetic counseling consequences.

The molecular basis of Angelman syndrome and Prader-Willi syndrome is well established, and genetic testing for these disorders is clinically available. Imprinting abnormalities account for up to 4% of patients with Angelman and Prader-Willi syndromes. Deletions of the imprinting center region are the molecular abnormality observed in a subset of Angelman and Prader-Willi syndrome cases with imprinting defects. Genetic testing of imprinting center deletions in patients with Angelman and Prader-Willi syndrome is not readily available. Such testing is important for the diagnostics of Angelman and Prader-Willi syndrome because it allows for more accurate diagnosis and recurrence risk prediction in families. Here we describe the development, validation, and implementation of a real time quantitative polymerase chain reaction (PCR)-based assay for imprinting center deletion detection in patients with Angelman and Prader-Willi syndrome, which we have incorporated into our genetic testing strategy for these disorders. To date we have tested, on a clinical basis, five patients with either Angelman or Prader-Willi syndrome in whom an imprinting center defect was implicated and found a deletion in one patient that was determined to be familial.

Angelman syndrome (AS) and Prader–Willi syndrome (PWS) are considered sister imprinting disorders. Although both AS and PWS congenital neurodevelopmental disorders have chromosome 15q11.3-q13 dysfunction, their molecular mechanisms differ owing to genomic imprinting, which results in different parent-of-the-origin gene expressions. Recently, several randomized controlled trials have been proceeded to treat specific symptoms of AS and PWS. Due to the advance of clinical management, early diagnosis for patients with AS and PWS is important. PWS is induced by multiple paternal gene dysfunctions, including those in MKRN3, MAGEL2, NDN, SNURF-SNPRPN, NPAP1, and a cluster of small nucleolar RNA genes. PWS patients exhibit characteristic facial features, endocrinological, and behavioral phenotypes, including short and obese figures, hyperphagia, growth hormone deficiency, hypogonadism, autism, or obsessive– compulsive-like behaviors. In addition, hypotonia, poor feeding, failure to thrive, and typical facial features are major factors for early diagnosis of PWS. For PWS patients, epilepsy is not common and easy to treat. Conversely, AS is a single-gene disorder induced by ubiquitin-protein ligase E3A dysfunction, which only expresses from a maternal allele. AS patients develop epilepsy in their early lives and their seizures are difficult to control. The distinctive gait pattern, excessive laughter, and characteristic electroencephalography features, which contain anterior-dominated, high-voltage triphasic delta waves intermixed with epileptic spikes, result in early suspicion of AS. Often, polytherapy, including the combination of valproate, levetiracetam, lamotrigine, and benzodiazepines, is required for controlling seizures of AS patients. Notably, carbamazepine, oxcarbazepine, and vigabatrin should be avoided, since these may induce nonconvulsive status epilepticus. AS and PWS presented with distinct clinical manifestations according to specific molecular defects due to genomic imprinting. Early diagnosis and teamwork intervention, including geneticists, neurologists, rehabilitation physicians, and pulmonologists, are important. Epilepsy is common in patients with AS, and after proper treatment, seizures could be effectively controlled in late childhood or early adulthood for both AS and PWS patients.