Nutrient intake and body composition variables in Prader-Willi syndrome--effect of growth hormone supplementation and genetic subtype.

UNLABELLED: In patients with Prader-Willi syndrome (PWS), limited information exists on the effects of growth hormone (GH) therapy, gender and genetic subtype on nutrient intake and body composition. We therefore compared GH-treated and nontreated patients, taking into account Tanner stage, gender, and genetic form. PATIENTS AND METHODS: In 37 individuals with PWS (20/17 M/F; 21/16 GH+/GH-), dietary intake and body composition (BMI, DEXA) were assessed. RESULTS: Older GH-treated children (Tanner stage 3-4) displayed improved body composition variables (BMI, total and percentage fat mass, truncal fat) (p < 0.05), despite dietary intake similar to non-treated patients; younger children (Tanner stage 1-2) displayed a different pattern, despite greater total caloric and fat intake (p < 0.05) with GH treatment, with only minor differences in body composition. Genetic form and gender had no intrinsic effect on nutrient intake or body composition. CONCLUSION: In 37 patients with PWS, GH treatment selectively affected body composition (BMI, fat mass), and dietary fat intake based on patients' developmental status, while these variables were unaffected by gender or genetic subtype.

Scanning for telomeric deletions and duplications and uniparental disomy using genetic markers in 120 children with malformations.

We screened 120 children with sporadic multiple congenital anomalies and either growth or mental retardation for uniparental disomy (UPD) or subtelomeric deletions. The screening used short tandem repeat polymorphisms (STRP) from the subtelomeric regions of 41 chromosome arms. Uninformative marker results were reanalyzed by using the next available marker on that chromosome arm. In total, approximately 25,000 genotypes were generated and analyzed for this study. Subtelomeric deletions of 1 Mb in size were excluded for 27 of 40 chromosome arms. Among the 120 subjects none was found to have UPD, but five subjects (4%, 95% confidence interval 1-9%) were found to have a deletion or duplication of one or more chromosome arms. We conclude that UPD is not a frequent cause of undiagnosed multiple congenital anomaly syndrome. In addition, we determined that 9p and 7q harbor chromosome length variations in the normal population. We conclude that subtelomeric marker analysis is effective for the detection of subtelomeric duplications and deletions, although it is labor intensive. Given a detection rate that is similar to prior studies and the large workload imposed by STRPs, we conclude that STRPs are an effective, but impractical, approach to the determination of segmental aneusomy given current technology.

The changing purpose of Prader-Willi syndrome clinical diagnostic criteria and proposed revised criteria.

BACKGROUND: Prader-Willi syndrome (PWS) is a complex, multisystem disorder. Its major clinical features include neonatal hypotonia, developmental delay, short stature, behavioral abnormalities, childhood-onset obesity, hypothalamic hypogonadism, and characteristic appearance. The genetic basis of PWS is also complex. It is caused by absence of expression of the paternally active genes in the PWS critical region on 15q11-q13. In approximately 70% of cases this is the result of deletion of this region from the paternal chromosome 15. In approximately 28%, it is attributable to maternal uniparental disomy (UPD; inheritance of 2 copies of a chromosome from the mother and no copies from the father, as opposed to the normal 1 copy from each parent) of chromosome 15, and in <2%, it is the result of a mutation, deletion, or other defect in the imprinting center. Clinical diagnostic criteria were established by consensus in 1993. Subsequently, definitive molecular genetic testing became available for laboratory diagnosis of PWS. However, identification of appropriate patients for testing remains a challenge for most practitioners because many features of the disorder are nonspecific and others can be subtle or evolve over time. For example, hypotonic infants who are still in the failure to thrive phase of the disorder often do not have sufficient features for recognition of PWS and often are not tested. Initial screening with these diagnostic criteria can increase the yield of molecular testing for older children and adults with nonspecific obesity and mental retardation. Therefore, the purpose of clinical diagnostic criteria has shifted from assisting in making the definitive diagnosis to raising diagnostic suspicion, thereby prompting testing. We conducted a retrospective review of patients with PWS confirmed with genetic testing to assess the validity and sensitivity of clinical diagnostic criteria published before the widespread availability of testing for all affected patients and recommend revised clinical criteria. METHODS: Charts of all 90 patients with laboratory-confirmed PWS were reviewed. For each patient, the presence or absence of the major, minor, and supportive features listed in the published diagnostic criteria was recorded. The sensitivity of each criterion, mean of the total number of major and minor criteria, and mean total score for each patient were calculated. RESULTS: There were 68 patients with a deletion (del 15q11-q13), 21 with maternal UPD of chromosome 15, and 1 with a presumed imprinting defect. Age range at the time of the most recent evaluation was 5 months to 60 years (median: 14.5 years; del median: 14 years; range: 5 months-60 years; UPD median: 18 years; range: 5-42 years). The sensitivities of the major criteria ranged from 49% (characteristic facial features) to 98% (developmental delay). Global developmental delay and neonatal hypotonia were the 2 most consistently positive major criteria and were positive in >97% of the patients. Feeding problems in infancy, excessive weight gain after 1 year, hypogonadism, and hyperphagia were all present in 93% or more of patients. Sensitivities of the minor criteria ranged form 37% (sleep disturbance and apneas) to 93% (speech and articulation defects). Interestingly, the sensitivities of 8 of the minor criteria were higher than the sensitivity of characteristic facial features, which is a major criterion. Fifteen out of 90 patients with molecular diagnosis did not meet the clinical diagnostic criteria retrospectively. CONCLUSION: When definitive diagnostic testing is not available, as was the case for PWS when the 1993 criteria were developed, diagnostic criteria are important to avoid overdiagnosis and to ensure that diagnostic test development is performed on appropriate samples. When diagnostic testing is available, as is now the case for PWS, diagnostic criteria should serve to raise diagnostic suspicion, ensure that all appropriate people are tested, and avoid the expense of testing unnecessarily. Our results indicate that the sensitivities of most of the published criteria are acceptable. However, 16.7% of patients with molecular diagnosis did not meet the 1993 clinical diagnostic criteria retrospectively, suggesting that the published criteria may be too exclusive. A less strict scoring system may ensure that all appropriate people are tested. Accordingly, we suggest revised clinical criteria to help identify the appropriate patients for DNA testing for PWS. The suggested age groupings are based on characteristic phases of the natural history of PWS. Some of the features (eg, neonatal hypotonia, feeding problems in infancy) serve to diagnose the syndrome in the first few years of life, whereas others (eg, excessive eating) are useful during early childhood. Similarly, hypogonadism is most useful during and after adolescence. Some of the features like neonatal hypotonia and infantile feeding problems are less likely to be missed, whereas others such as characteristic facial features and hypogonadism (especially in prepubertal females) may require more careful and/or expert examination. The issue of who should have diagnostic testing is distinct from the determination of features among confirmed patients. Based on the sensitivities of the published criteria and our experience, we suggest testing all newborns/infants with otherwise unexplained hypotonia with poor suck. For children between 2 and 6 years of age, we consider hypotonia with history of poor suck associated with global developmental delay sufficient criteria to prompt testing. Between 6 and 12 years of age, we suggest testing those with hypotonia (or history of hypotonia with poor suck), global developmental delay, and excessive eating with central obesity (if uncontrolled). At the ages of 13 years and above, we recommend testing patients with cognitive impairment, excessive eating with central obesity (if uncontrolled), and hypogonadotropic hypogonadism and/or typical behavior problems (including temper tantrums and obsessive-compulsive features). Thus, we propose a lower threshold to prompt diagnostic DNA testing, leading to a higher likelihood of diagnosis of this disorder in which anticipatory guidance and intervention can significantly influence outcome.

Prader-Willi and Angelman syndromes: sister imprinted disorders.

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are clinically distinct complex disorders mapped to chromosome 15q11-q13. They both have characteristic neurologic, developmental, and behavioral phenotypes plus other structural and functional abnormalities. However, the cognitive and neurologic impairment is more severe in AS, including seizures and ataxia. The behavioral and endocrine disorders are more severe in PWS, including obsessive-compulsive symptoms and hypothalamic insufficiency. Both disorders can result from microdeletion, uniparental disomy, or an imprinting center defect in 15q11-q13, although the abnormality is on the paternally derived chromosome 15 for PWS and the maternally derived 15 for AS because of genomic imprinting. Although the same gene may control imprinting for both disorders, the gene(s) causing their phenotypes differ. AS results from underexpression of a single gene, UBE3A, which codes for E6-AP, a protein that functions to transfer small ubiquitin molecules to certain target proteins, to enable their degradation. The genes responsible for PWS are not determined, although several maternally imprinted genes in 15q11-q13 are known. The most likely candidate is SNRPN, which codes for a small nuclear ribonucleoprotein, a ribosome-associated protein that controls gene splicing and thus synthesis of critical proteins in the brain. Animal models exist for both disorders. The genetic relationship between PWS and AS makes them unique and potentially highly instructive disorders that contribute substantially to the population burden of cognitive impairment.

Molecular cytogenetics of a de novo interstitial deletion of chromosome arm 6q in a developmentally normal girl.

Using fluorescence in situ hybridization and microsatellite analysis, we have characterized a de novo interstitial deletion on the long arm of chromosome 6 [46,XX,del(6) (q23.3q24.2)] in a developmentally normal girl with very mild phenotypic abnormalities. The deletion was paternal in origin and was between markers WI-5023 and D6S1042. The size of the deletion was estimated to be approximately 4-5 Mb. The normal phenotype in this patient might be the result of imprinting of paternal copies of genes located in the segment 6q23. 3-q24.2. Alternatively, the genes located in the segment 6q23.3-q24. 2 might not be subject to dosage effects and therefore the haploinsufficiency of genes in this segment might not have phenotypic consequences.

Chromosome breakage in the Prader-Willi and Angelman syndromes involves recombination between large, transcribed repeats at proximal and distal breakpoints.

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are distinct neurobehavioral disorders that most often arise from a 4-Mb deletion of chromosome 15q11-q13 during paternal or maternal gametogenesis, respectively. At a de novo frequency of approximately.67-1/10,000 births, these deletions represent a common structural chromosome change in the human genome. To elucidate the mechanism underlying these events, we characterized the regions that contain two proximal breakpoint clusters and a distal cluster. Novel DNA sequences potentially associated with the breakpoints were positionally cloned from YACs within or near these regions. Analyses of rodent-human somatic-cell hybrids, YAC contigs, and FISH of normal or rearranged chromosomes 15 identified duplicated sequences (the END repeats) at or near the breakpoints. The END-repeat units are derived from large genomic duplications of a novel gene (HERC2), many copies of which are transcriptionally active in germline tissues. One of five PWS/AS patients analyzed to date has an identifiable, rearranged HERC2 transcript derived from the deletion event. We postulate that the END repeats flanking 15q11-q13 mediate homologous recombination resulting in deletion. Furthermore, we propose that active transcription of these repeats in male and female germ cells may facilitate the homologous recombination process.

Maladaptive behavior differences in Prader-Willi syndrome due to paternal deletion versus maternal uniparental disomy.

Maladaptive behavior was compared across 23 people with Prader-Willi syndrome due to paternal deletion to 23 age- and gender-matched subjects with maternal uniparental disomy. Controlling for the higher IQs of the uniparental disomy group, deleted cases showed significantly higher maladaptive ratings on the Child Behavior Checklist's Internalizing, Externalizing, and Total domains as well as more symptom-related distress on the Yale-Brown Obsessive-Compulsive Scale. Across both measures, deleted cases were more apt to skin-pick, bite their nails, hoard, overeat, sulk, and withdraw. A dampening of symptom severity is suggested in Prader-Willi syndrome cases due to maternal uniparental disomy. Findings are compared to Angelman syndrome, and possible genetic mechanisms are discussed, as are implications for Prader-Willi syndrome and obsessive-compulsive behaviors.

Molecular mechanism of angelman syndrome in two large families involves an imprinting mutation.

Patients with Angelman syndrome (AS) and Prader-Willi syndrome with mutations in the imprinting process have biparental inheritance but uniparental DNA methylation and gene expression throughout band 15q11-q13. In several of these patients, microdeletions upstream of the SNRPN gene have been identified, defining an imprinting center (IC) that has been hypothesized to control the imprint switch process in the female and male germlines. We have now identified two large families (AS-O and AS-F) segregating an AS imprinting mutation, including one family originally described in the first genetic linkage of AS to 15q11-q13. This demonstrates that this original linkage is for the 15q11-q13 IC. Affected patients in the AS families have either a 5.5- or a 15-kb microdeletion, one of which narrowed the shortest region of deletion overlap to 1.15 kb in all eight cases. This small region defines a component of the IC involved in AS (ie., the paternal-to-maternal switch element). The presence of an inherited imprinting mutation in multiple unaffected members of these two families, who are at risk for transmitting the mutation to affected children or children of their daughters, raises important genetic counseling issues.

Molecular refinement of karyotype: beyond the cytogenetic band.

PURPOSE: Illustrate the use of molecular methodologies to delineate subtle, de novo, chromosome aberrations and determine the presence, or absence, of known genes, allowing improved predictions of long-term phenotypic effect. METHOD: High-resolution chromosome analysis followed by FISH and microsatellite analysis to determine the extent and parental origin of the abnormalities. RESULTS: Four de novo deletions involving chromosomes 5q, 10q, and 16p were delineated molecularly. Specific genes were shown to be, or not to be, involved in each aberration, refining karyotype-genotype correlation. CONCLUSION: Molecular characterization of subtle chromosomal aberrations can provide information to assist in predicting clinical outcome in cases involving genes known to have an effect due to haploinsufficiency or aberrant gene dosage.

Molecular characterization and delineation of subtle deletions in de novo "balanced" chromosomal rearrangements.

To test the hypothesis that the phenotypic abnormalities seen in cases with apparently balanced chromosomal rearrangements are the result of the presence of cryptic deletions or duplications of chromosomal material near the breakpoints, we analyzed three cases with apparently balanced chromosomal rearrangements and phenotypic abnormalities. We characterized the breakpoints in these cases by using microsatellite analysis by polymerase chain reaction and fluorescence in situ hybridization analysis of yeast artificial chromosome clones selected from the breakpoint regions. Molecular characterization of the translocation breakpoint in patient 1 [46,XY,t(2;6)(p22.2;q23.1)] showed the presence of a 4- to 6-Mb cryptic deletion between markers D6S412 and D6S1705 near the 6q23.1 breakpoint. Molecular characterization of the proximal inversion 7q22.1 breakpoint in patient 2 [46,XY,inv(7)(q22.1q32.1)] revealed the presence of a 4-Mb cryptic deletion between D7S651 and D7S515 markers. No deletion or duplication of chromosomal material was found near the breakpoints in patient 3 [46,XX,t(2;6)(q33.1;p12.2)]. Our study suggests that a systematic molecular study of breakpoints should be carried out in cases with apparently balanced chromosomal rearrangements and phenotypic abnormalities, because cryptic deletions near the breakpoints may explain the phenotypic abnormalities in these cases.

Aortic root dilatation in Ehlers-Danlos syndrome types I, II and III. A report of five cases.

We have identified five families in whom individuals affected with the Ehlers Danlos syndrome (EDS) types I, II or III had aortic root dilatation (ARD). All propositi had a low upper/lower segment ratio but no other diagnostic skeletal or ocular features of Marfan syndrome. Their skin had the soft, velvety texture characteristic of EDS and all had significant joint laxity. Probands included a 4-year-old girl with EDS type I, 4- and 8-year-old girls with EDS type III, a 35-year-old male with EDS type II, and a 51-year-old female with EDS type III. Review of these cases suggests the need for multicenter clinical studies in order to determine the prevalence and the rate of progression of ARD in EDS types I, II, and III. Such studies are necessary to determine whether echocardiograms (including measurement of aortic root diameter) should be considered on initial evaluation of all patients with mild forms of EDS.

Prader-Willi and Angelman syndromes. Disorders of genomic imprinting.

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.

Deletion 10q23.2-q23.33 in a patient with gastrointestinal juvenile polyposis and other features of a Cowden-like syndrome.

A cytogenetically visible interstitial deletion of chromosome band 10q23 was found in a 6-year-old boy with mental retardation, dysmorphic features, and juvenile polyposis coli. In order to map this patient's deletion physically, we performed fluorescence in situ hybridization by using yeast artificial chromosomes (YACs) in the vicinity of the deletion. Five YACs that span an 11-15 cM region within the deletion were identified. This patient's deletion contains the putative locus for Cowden syndrome and a recently discovered candidate tumor suppressor gene (MMAC1 or PTEN) that has been implicated in the progression of a variety of human malignancies. Furthermore, the deletion is near and possibly overlaps a locus associated with juvenile polyposis. The findings in this patient with a constitutional 10q23 deletion raise the issue of whether there are separate genes in this region that are involved in Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, juvenile polyposis, and tumor progression, or whether all of these entities could be due to a single gene.

Phenotypic differerencss in African Americans with Prader-Willi syndrome.

We report on 10 African Americans with Prader-Willi syndrome whose features differ from those of white patients with this condition. Growth is less affected, hand and foot lengths usually are normal, and the facies are atypical; this may lead to underdiagnosis in this population. We encourage clinicians to recognize these phenotypic differences so that diagnosis is not overlooked.

Prader-Willi syndrome.

Prader-Willi syndrome is a complex disorder affecting multiple systems with many manifestations relating to hypothalamic insufficiency. Major findings include infantile hypotonia, developmental delay and mental retardation, behaviour disorder, characteristic facial appearance, obesity, hypogonadism, and short stature. Obesity and the behavioural problems are the major causes of morbidity and mortality. Prader-Willi syndrome is caused by abnormalities of the imprinted region of proximal 15q and results from absence of the normally active paternal genes in this region. Such absence results from paternal interstitial deletion, maternal uniparental disomy, or a mutation or other abnormality in the imprinting process. Diagnostic identification of all causes has become available in recent years, permitting early detection and institution of appropriate management. This testing has permitted recent identification of some phenotypic differences among affected subjects of different race and between those with deletions and uniparental disomy as a cause.

Balanced translocation 46,XY,t(2;15)(q37.2;q11.2) associated with atypical Prader-Willi syndrome.

The lack of normally active paternal genes in 15q11-q13, as an outcome of either a paternal deletion or maternal disomy, accounts for >95% of all patients with Prader-Willi syndrome. Other mechanisms, including imprinting mutations and unbalanced translocations involving pat 15q11-q13, have been described elsewhere. In this study, we present a patient with a rare balanced, de novo translocation-46,XY,t(2;15)(q37.2;q11.2)-involving breakage within the Prader-Willi/Angelman syndrome region of the paternal homologue, without an apparent deletion. The patient demonstrated several manifestations of the Prader-Willi syndrome but was clinically atypical. Cytogenetic and molecular studies of this case demonstrated the translocation breakpoint to be between SNRPN and IPW, with mRNA expression of SNRPN and PAR-5 but absence of IPW and PAR-1 expression. These results suggest that disruption of either IPW expression or a nearby gene by an upstream break may contribute to the Prader-Willi syndrome phenotype and that expression of SNRPN or other upstream genes is responsible for other aspects of the classical Prader-Willi syndrome phenotype.