Expression of 4 genes between chromosome 15 breakpoints 1 and 2 and behavioral outcomes in Prader-Willi syndrome

Prader-Willi syndrome is a neurodevelopmental disorder that is characterized by infantile hypotonia, feeding difficulties, hypogonadism, mental deficiency, hyperphagia (leading to obesity in early childhood), learning problems, and behavioral difficulties. A paternal 15q11-q13 deletion is found in approximately 70% of patients with Prader-Willi syndrome, approximately 25% have uniparental maternal disomy 15, and the remaining 2% to 5% have imprinting defects. The proximal deletion breakpoint in the 15q11-q13 region occurs at 1 of 2 sites located within either of 2 large duplicons allowing for the identification of 2 deletion subgroups. The larger, type I (TI) deletion involves breakpoint 1, which is close to the centromere, whereas the smaller, type II (TII) deletion involves breakpoint 2, located approximately 500 kilobases distal to breakpoint 1. Breakpoint 3 is located at the distal end of the 15q11-q13 region and common to both typical deletion subgroups. Analyses of the genetic subtypes of Prader-Willi syndrome to date have primarily compared individuals with typical deletion and uniparental maternal disomy 15 without grouping the individuals with a deletion into TI or TII. Distinct differences have been reported between individuals with Prader-Willi syndrome resulting from deletion compared with uniparental maternal disomy 15 in physical, cognitive, and behavioral parameters. We previously presented the first assessment of clinical differences in individuals with Prader-Willi syndrome categorized as having type I or II deletions. Adaptive behavior, obsessive-compulsive behaviors, reading, math, and visual-motor integration assessments were generally poorer in individuals with Prader-Willi syndrome and the TI deletion compared with subjects with Prader-Willi syndrome with the TII deletion or uniparental maternal disomy 15. Four genes (NIPA1, NIPA2, CYFIP1, and GCP5) have been identified in the chromosomal region between breakpoints 1 and 2 and are implicated in compulsive behavior and lower intellectual ability observed in individuals with Prader-Willi syndrome with TI versus TII deletions. We quantified messenger-RNA levels of these 4 genes in actively growing lymphoblastoid cells derived from 8 subjects with Prader-Willi syndrome with the TI deletion (4 males, 4 females; mean: age 25.2 +/- 8.9 years) and 9 with the TII deletion (3 males, 6 females; mean age: 19.5 +/- 5.8 years). Messenger-RNA levels were correlated with validated psychological and behavioral scales administered by trained psychologists blinded to genotype status. Messenger RNA from NIPA1, NIPA2, CYFIP1, and GCP5 was reduced but detectable in the subjects with Prader-Willi syndrome with the TI deletion, supporting biallelic expression. For the most part, messenger-RNA values were positively correlated with assessment parameters, indicating a direct relationship between messenger-RNA levels and better assessment scores, with the highest correlation for NIPA2. The coefficient of determination indicated the quantity of messenger RNA of the 4 genes explained from 24% to 99% of the variation of the behavioral and academic parameters measured. By comparison, the coefficient of determination for deletion type alone explained 5% to 50% of the variation in the assessed parameters. Understanding the influence of gene expression on behavioral and cognitive characteristics in humans is in the early stage of research development. Additional research is needed to identify the function of these genes and their interaction with gene networks to clarify the potential role they play in central nervous system development and function.     

Prader–Willi syndrome

Prader-Willi syndrome is a multi system disorder characterized by neonatal hypotonia, later obesity, hyperphagia and mental retardation. It occurs sporadically, either as a result of microdeletion of chromosome 15p (70%) or as a result of maternal disomy of chromosome 15 (30%). The major problems encountered by parents are those of hyperphagia, food-seeking and obesity, and conduct disorder, particularly tantrums or oppositional behaviour.     

Prader-Willi syndrome: intellectual abilities and behavioural features by genetic subtype

BACKGROUND: Studies of chromosome 15 abnormality have implicated over-expression of paternally imprinted genes in the 15q11-13 region in the aetiology of autism. To test this hypothesis we compared individuals with Prader-Willi syndrome (PWS) due to uniparental disomy (UPD--where paternally imprinted genes are over-expressed) to individuals with the 15q11-13 deletion form of the syndrome (where paternally imprinted genes are not over-expressed). We also tested reports that PWS cases due to the larger type I (TI) form of deletion show differences to cases with the smaller type II (TII) deletion. METHOD: Ninety-six individuals with PWS were recruited from genetic centres and the PWS association. Forty-nine individuals were confirmed as having maternal UPD of chromosome 15 and were age and sex matched to 47 individuals with a deletion involving 15q11-13 (32 had the shorter (T II) deletion, and 14 had the longer (TI) deletion). Behavioural assessments were carried out blind to genetic status, using the Autism Diagnostic Observation Schedule (ADOS), the Autism Diagnostic Interview (ADI), the Autism Screening Questionnaire (ASQ), the Children's Yale-Brown Obsessive-Compulsive Scale (CY-BOCS), the Vineland Adaptive Behaviour Scales (VABS), and measurements of intellectual ability, including the Wechsler and Mullen Scales and Raven's Matrices. RESULTS: UPD cases exhibited significantly more autistic-like impairments in reciprocal social interaction on questionnaire, interview and standardised observational measures. Comparison of TI and TII deletion cases revealed few differences, but ability levels tended to be lower in the TI deletion cases. CONCLUSIONS: Findings from a large study comparing deletion and UPD forms of Prader-Willi syndrome were consistent with other evidence in indicating that paternally imprinted genes in the 15q11-13 region constitute a genetic risk factor for aspects of autistic symptomatology. These genes may therefore play a role in the aetiology of autism. By contrast with another report, there was no clear-cut relationship between the size of the deletion and the form of cognitive and behavioural phenotype.     

Comparison of high resolution cytogenetics, fluorescence in situ hybridisation, and DNA studies to validate the diagnosis of Prader-Willi and Angelman's syndromes

Eighty seven referrals with Prader-Willi syndrome and 49 with Angelman's syndrome were studied. High resolution cytogenetics was performed on all probands. Molecular studies, performed on the proband and both parents in each case, utilised multiple probes from within and distal to the 15(q11-13) region in order to establish the presence of DNA deletion or uniparental disomy. In addition, FISH, with probes at D15S11 and GABR beta 3 from the Prader-Willi syndrome/Angelman's syndrome region, was performed on a subset of 25 of these patients. In the referral group with Prader-Willi syndrome, 62 patients had a normal karyotype and 25 were deleted on high resolution cytogenetics. Twenty nine were found to be deleted with DNA techniques. In the Angelman's syndrome group, 37 had a normal karyotype and 12 were deleted on high resolution cytogenetics while 26 were deleted on molecular studies. The diagnosis was reassessed in 35 referrals with Prader-Willi syndrome and 11 with Angelman's syndrome following a non-deleted, non-disomic result. Of individuals who were neither deleted nor disomic on DNA studies, a false positive rate of 11.4% (4/35) for Prader-Willi syndrome and 16.7% (2/12) for Angelman's syndrome was found for a cytogenetically detected deletion. The false negative rate for deletion detected on high resolution cytogenetics was 19.5% (12/62) for Prader-Willi syndrome and 35% (13/37) for Angelman's syndrome. Thus high resolution cytogenetics was shown to be unreliable for deletion detection and should not be used alone to diagnose either syndrome. There were no discrepancies with FISH in 25 cases when FISH was compared with the DNA results, indicating that FISH can be used reliably for deletion detection in both syndromes.     

Lessons from fragile X regarding neurobiology, autism, and neurodegeneration

The fragile X mental retardation 1 gene (FMR1) mutation causes two disorders: fragile X syndrome (FXS) in those with the full mutation and the fragile X-associated tremor/ataxia syndrome (FXTAS) in some older individuals with the premutation. FXS is caused by a deficiency of the FMR1 protein (FMRP) leading to dysregulation of many genes that create a phenotype with ADHD, anxiety, and autism. FXTAS is caused by the elevation of FMR1-mRNA to levels 2 to 8 times normal in the premutation. This causes an RNA gain of function toxicity leading to brain atrophy, white matter disease, neuronal and astrocytic inclusion formation, and subsequent ataxia, intention tremor, peripheral neuropathy, and cognitive decline. The neurobiology and pathophysiology of FXS and FXTAS are described in detail.     

自行设计的多重链接探针扩增组合对多发畸形患儿的诊断价值

目的 尝试基于多重链接探针扩增（MLPA）技术设计的探针组合对多发畸形(MCA)患儿的诊断价值。方法 以临床发现≥2个的畸形表型患儿为病例,基于MLPA技术选择13种常见的MCA的关键基因和关键区域自行设计MLPA探针组合（SIGMA公司合成）,以微阵列比较基因组杂交（aCGH）作为金标准,检验该探针组合的诊断准确性,再以MLPA探针组合行MCA临床诊断效果评估,对MLPA探针组合阳性的病例结合临床资料进行分析。结果 ①MLPA探针组合涉及的13种常见MCA,包括：21-三体综合征（KCNJ6、DYRK1A、RCAN1基因）、18-三体综合征（MC2R、DTNA、TCF4基因）、13-三体综合征（EDNRB、CENPJ、ERCC5、FREM2基因）、1p36区域缺失综合征（GABRD、SKI、TP73基因）、 5q35.3区域缺失综合征（Sotos综合征,NSD1基因）、CHARGE综合征（CHD7基因）、7q11.23区域缺失综合征（Williams Beuren综合征,CLIP2、ELN、LIMK1基因）;22q11.21区域缺失、重复综合征（DiGeorge综合征,SNAP29、TBX1、ZNF74基因）、17p11区域缺失综合征（Smith-Magenis综合征,RAI1、MFAP4基因）、5p15.2区域缺失综合征（Cri du Chat综合征, CTNND2、TERT基因）、15q11-13区域缺失综合征（Prader-Willi综合征,OCA2、UBE3A、GABRB3基因）、4p16.3区域缺失综合征（Wolf Hirschhorn综合征,MSX1、WHSC1、LETM1基因）、17q21.31区域缺失综合征（MAP3K14、MAPT基因）。②35例MCA中,aCGH检测阳性11例（31.4%）,共诊断9种;MLPA探针组合检测阳性6例（17.1%）,共诊断4种;MLPA组合探针检测阳性的6例微缺失和重复与11例aCGH检测阳性一致,6例MLPA探针组合检测阳性的变异位点均位于设计的MLPA探针组合中,122例临床MCA中,MLPA探针组合检测阳性21例（17.2%）,诊断6种。③在157例MCA患儿中,应用MLPA探针组合共诊断阳性病例27例,共检出7种（53.8%）,分别为21-三体综合征8例,18-三体综合征1例,5p15区域缺失综合征3例,22q11区域重复综合征1例、缺失综合征9例,5q35区域缺失综合征1例,15q11-q13区域缺失综合征3例,7q11.23区域微缺失综合征1例。结论 自行设计合成的MLPA探针组合对非典型临床表型的MCA病例有较好的诊断价值。     

Behavior in Prader-Willi syndrome: relationship to genetic subtypes and age

Background:  Some behavioral features of Prader-Willi syndrome (PWS) are associated with the major genetic subtypes of this disorder. While most agree that those with maternal uniparental disomy (UPD) have a distinctive cognitive and psychiatric profile, findings are more controversial regarding possible differences among persons who vary in paternal deletion size.
Methods:  Caregivers of 88 persons with PWS aged 5 to 51 years ( M  =   22 years) were administered measures of problem behavior, compulsivity, hyperphagia, and adaptive skills. The sample was well characterized as having relatively large, Type I ( n  =   26) or smaller, Type II ( n  =   29) deletions, or UPD ( n  =   33).
Results:  No significant behavioral differences were found between the Type I versus Type II deletion groups. Within each genetic subtype, however, differences emerged in how advancing age related to behavior. Although age did not emerge as a significant correlate of behavior in the Type II or UPD groups, in the Type I group age was consistently associated with lower problem behaviors, adaptive skills, and externalizing symptoms.
Conclusion:  Although differences between deletion subtypes were not found, significant within-subtype differences emerged in relationships between age and behavior. Negative associations between age and behavior in the Type I group only may relate to non-imprinted genes that are deleted in Type I but not Type II cases, including CYFIP1. Altered expression of CYFIP1 is seen in other developmental disabilities, including 15q disorders, and haploinsufficiency of CYFIP1 in Type I PWS cases may be associated with age-related phenotypic effects. Findings underscore the importance of a life-span perspective in phenotypic research.     

4例女性Prader-Willi综合征患儿的内分泌代谢特点

4例Prader-Willi综合征(PWS)患儿均为女性,确诊年龄6~12岁,均有肥胖,特殊面容,发育迟缓、智力障碍等临床表现,遗传学检测提示其中2例为15q11.2-q13区域父源性缺失,1例为15q11.2-q13区域母源性同源二倍体,1例15q11.2-q13区域未发现异常。4例患者存在不同程度的内分泌代谢紊乱:2例身材矮小,其中1例第二性征延迟,另1例合并2型糖尿病;1例表现为胰岛素抵抗,无乳腺发育;1例患儿的身高处于P_3~P_(10),性早熟。PWS患者存在多种内分泌功能紊乱,长期内分泌专科随访及管理十分重要。     

Diagnosis of the Prader-Willi syndrome by proving the absence of the unmethylated PW71 DNA fragment

The Prader-Willi syndrome (PWS) is a genetic disorder which is difficult to diagnose from clinical symptoms in newborns and young children. However, it is known that in PWS a fragment within the q11-13 region of the paternally derived chromosome 15 is deleted. Recently it has been observed that the D15S63 (PW71) locus in chromosome 15q11-13 is methylated on the maternally derived chromosome, but unmethylated on the paternally derived chromosome. Based on this observation a rapid diagnostic test (the PW71 methylation test) using methylation-sensitive restriction enzymes has been developed for patients presumed to have PWS. We have studied 56 patients; 30 patients with classical features of PWS and 26 patients with only psychomotor retardation and obesity, referred to us from different parts of Sweden. Twenty-nine of the 30 classical PWS patients were found to have an absence of the unmethylated paternally derived PW71(D15S63) locus in chromosome 15q11-13. None of the patients with only obesity and psychomotor retardation had this "absence" pattern on chromosome 15q11-13. Using the PW71 methylation test on patients with PWS, a concordance of 96% was found. The PW71 methylation test is presently the method of choice for rapid diagnostic testing of patients suspected of having PWS.     

Interstitial 6q deletion with a Prader-Willi-like phenotype: a new case and review of the literature.

We report on an additional fourth case of Prader-Willi (PW)-like phenotype and an interstitial deletion of 6q. Despite sharing clinical characteristics, patients with a PW-like phenotype and a deletion of 6q, have features which distinguish them from Prader-Willi syndrome (PWS) patients. This case emphasizes the need to examine patients with suspected PWS, but who are negative for recognizable deletions of 15q11-q13 or uniparental maternal disomy of chromosome 15, for a deletion of 6q.     

Hypotonic infants and the Prader-Willi Syndrome

OBJECTIVE: To describe 6 patients with less than 3 years of age that were diagnosed with Prader-Willi syndrome (PWS) due to hypotonia, poor sucking, slight facial anomalies and minor abnormalities of hands and feet. PWS is a neurobehavioural disorder characterized by two distinct phases; in the first, the neonate presents variable degree of hypotonia, feeding problems with none or poor sucking; hypogonadism, characteristic facial features with almond shaped eyes, narrow bifrontal diameter and down-turned corners of the mouth. Neuropsichymotor development is delayed. Hypotonia is non progressive and tends to improve between 8 and 11 months of age. The second phase then starts and is characterized by increasing hyperphagia and obesity, among other features. Unfortunately, most PWS patients are diagnosed only after obesity is installed. METHODS: Methylation, microsatellites analysis and karyotypic studies by traditional and in situ hybridization techniques were done. RESULTS: A deletion of chromosome segment 15q11q13 was disclosed in 4 and maternal disomy in two patients. CONCLUSION: The diagnosis of PWS is generally established after the onset of obesity. So, we suggest that the genetic analysis must be carried out in children with severe hypotonia of unknown cause, poor sucking and some facial features of PWS (small hands and feet, hypogonadism, hypopigmentation, almond eyes and narrow bifrontal diameter). This can allow the early diagnosis and avoid invasive exams necessary for neuromuscular disorder diagnosis like muscle biopsy and electroneuromiography, wich frequently are associated with inconclusives results.     

Treatment of precocious puberty in a female with Prader-Willi syndrome

Prader-Willi syndrome (PWS) is characterized by neonatal hypotonia, hyperphagia, childhood obesity at an early age, short stature, varying degrees of mental deficiency, and hypogonadism. In PWS, puberty is usually delayed and fails to complete, with most females never having regular menstrual cycles. We report a female patient with uniparental disomy, who experienced precocious puberty with menarche at age 8 years. The patient was treated with luteinizing hormone releasing hormone (LHRH) analog, which suppressed pubertal development. From our search of the literature this is the first application of LHRH analog to a female PWS patient for precocious puberty. Use of LHRH analog along with recombinant human growth hormone (rhGH) permitted stature closer to target height. The clinical course of this patient with PWS underscores the need for individualized treatment.     

Neonatal presentation of Prader Willi sindrome. Personal records

Prader Willi Syndrome (PWS) is characterized by typical appearance, obesity, short stature, hypothalamic hypogonadism, cryptorchidism, hypotonia, behavioural abnormalities and mental retardation. It is considered as a continuous genes syndrome with different genotypes: microdeletion of the region 15q11-q13 with paternal imprinting; maternal uniparental disomy (UPD) of chromosome 15; chromosomal rearrangement. Clinical manifestations evolve with age from newborn (hypotonia, poor sucking, hypoplastic external genitalia) to childhood (delay in psychomotor development, hyperphagia, obesity, acromicria and craniofacial dysmorphisms). We present five newborns who received an early diagnosis, based on clinical presentation. The early treatment and follow-up can in fact improve the natural evolution of the syndrome in order to prevent respiratory tract diseases and obesity, and to improve growth.     

Glucose homeostasis in Prader-Willi syndrome and potential implications of growth hormone therapy

Diabetes mellitus is becoming a more frequently recognized complication of Prader-Willi syndrome. It has been reported that as many as 7-20% of individuals with Prader-Willi syndrome may develop this complication. Diabetes mellitus adds to the complexity of an already complex treatment program, causes many serious complications that greatly affect the quality of life of these individuals, and can lead to serious morbidity and mortality. Recent studies suggest that growth hormone (GH) might offer significant advantages to individuals with Prader-Willi syndrome. However, as a known diabetogenic agent, GH might also increase the propensity to develop diabetes mellitus. For this reason, the characteristics of the diabetes mellitus that develops in individuals with Prader-Willi syndrome must be studied and fully understood. The initial assumption has been that the diabetes mellitus associated with this syndrome is identical to that seen in obese individuals without Prader-Willi syndrome, in whom genetic factors and obesity lead to insulin resistance. Severe insulin resistance in turn leads to pancreatic failure and hence the symptom complex of type 2 diabetes mellitus. To determine if this same pattern is present in patients with Prader-Willi syndrome, we evaluated both obese children and adults with the syndrome. These patients were compared with obese individuals without Prader-Willi syndrome matched for age, gender and weight and who had not yet developed diabetes but had equally longstanding obesity. We compared the glucose and insulin responses of these two groups, using both oral and intravenous glucose challenges. The results demonstrated that individuals with Prader-Willi syndrome do not show the predicted insulin resistance that is seen in obese children without the syndrome. In fact, the individuals with Prader-Willi syndrome showed normal or increased insulin sensitivity. These data do not support the hypothesis that the high incidence of diabetes mellitus in patients with Prader-Willi syndrome is simply the result of obesity and therefore suggest a different aetiology.     

Autistic spectrum disorder and the fragile X premutation

Fragile X syndrome (FXS) is the most common inherited cause of mental retardation. It is also one of the most common identifiable causes of Autism Spectrum Disorder (ASD). Carriers of FXS are often considered to be cognitively and behaviorally unaffected. However, we report here on six individuals in the premutation range who also have ASD. A comparison is made with five subjects in the premutation range who did not receive a diagnosis of ASD. The six individuals with ASD had a range of cognitive ability levels from no impairment to moderate retardation. Discussion includes the impact of molecular variables including lowered FMR1 protein and elevated FMR1 mRNA in addition to environmental factors leading to the complex neurodevelopmental disorder of ASD.     

Unique maternal deletion of 15q in a patient with some symptoms of Prader-Willi syndrome

BACKGROUND: Human chromosome 15q11-q13 is a critical region for Prader-Willi syndrome (PWS) and Angelman syndrome (AS) and most of the genes are under the condition of imprinting mechanism. PWS results from the loss of expression of paternally expressed genes and AS of maternally expressed genes. In this study molecular studies about a patient with congenital anomalies and mental retardation are analyzed. METHODS: Highly polymorphic microsatellite markers were analyzed by PCR. These markers exist within 15q11-q13 and distal to 15q13. RESULTS: Only the maternal D15S986 locus within 15q11-q13 was deleted and other markers were biallelic. CONCLUSIONS: The result of maternal small region deletion in this patient is different from the typical PWS with paternal chromosome deletion and it suggests that nearby the deleted region there exists a gene (genes) which is not imprinted but needs biallelic expression.     

新生儿Prader-Willi综合征13例临床表型分析

目的 分析Prader-Willi综合征（PWS）新生儿期的临床表现,为临床早期筛选及进一步行分子诊断提供帮助。方法 回顾性分析2009年8月至2011年8月在北京军区总医院附属八一儿童医院依据MS-PCR和MS-MLPA方法确诊为PWS患儿的诊断、分型和临床表型资料,分析中国PWS新生儿期典型特征。结果 13例PWS进入分析,男9例,女4例,确诊年龄4～28 d。足月儿10例,早产儿2例,过期产儿1例。孕母高龄9例（69.2%）,羊水污染8例（61.5%）,羊水过多3例（23.1%）,胎膜早破5例（38.5%）,异常胎位4例（30.8%）,宫内窘迫9例（69.2%）。 9例为父源性15q11.2-q13区域缺失致病,4例为母源性同源二倍体。4例母源性同源二倍体患儿均可见中枢性肌张力低下和皮肤色素减退,吸吮缓慢2例(50.0%)、哭声微弱3例(75.0%)、男性隐睾1例(25.0%)、女性小阴唇3例(75.0%);均未见特殊面容和唾液黏稠,均不需特殊喂养。9例父源性15q11.2-q13区域缺失患儿均可见中枢性肌张力低下、皮肤色素减退和哭声微弱,吸吮缓慢2例(22.2%)、需特殊喂养7例(77.8%)、特殊面容5例(55.6%)、男性隐睾7例(77.8%)、阴茎短小4例（44.4%）、女性小阴唇1例(11.1%)、唾液黏稠5例(55.6%)。结论 母源性同源二倍体患儿的特殊面容和男性生殖器发育不全的发生率低于父源性15q11.2-q13区域缺失患儿。新生儿期皮肤色素减退及中枢性肌张力低下是中国PWS新生儿普遍存在的特征,可作为进一步行PWS分子诊断的初步筛选指标。     

Genetic abnormalities in Prader-Willi syndrome and lessons from mouse models

Prader-Willi syndrome is a multigenic disorder with developmental and neurobehavioural abnormalities. There are multiple genetic causes, although all ultimately involve the loss of paternally derived gene expression of chromosome region 15q11-q13. Multiple imprinted genes expressed only from the paternal allele have been identified in the specific region of human chromosome 15q associated with Prader-Willi syndrome and in the syntenic mouse chromosome 7C region, including a novel polycistronic gene (SNURF-SNRPN) that encodes two independent proteins. The latter genetic locus may play a key role in Prader-Willi syndrome and the evolution of imprinting in this domain, because it is uniquely involved with mutations in the imprinting process and balanced translocations in this syndrome. Indeed, based on the co-localization of SNURF and SNRPN within the imprinting control region critical to Prader-Willi syndrome, evolutionary arguments would suggest that this genetic locus is a prime candidate for mutations producing the failure-to-thrive phenotype of neonates with this syndrome and of corresponding mouse models. Hence, the SNURF-SNRPN gene may encode a paternally derived postnatal growth factor.     

Genetic abnormalities in Prader-Willi syndrome and lessons from mouse models

Prader-Willi syndrome is a multigenic disorder with developmental and neurobehavioural abnormalities. There are multiple genetic causes, although all ultimately involve the loss of paternally derived gene expression of chromosome region 15q11-q13. Multiple imprinted genes expressed only from the paternal allele have been identified in the specific region of human chromosome 15q associated with Prader-Willi syndrome and in the syntenic mouse chromosome 7C region, including a novel polycistronic gene ( SNURF-SNRPN ) that encodes two independent proteins. The latter genetic locus may play a key role in Prader-Willi syndrome and the evolution of imprinting in this domain, because it is uniquely involved with mutations in the imprinting process and balanced translocations in this syndrome. Indeed, based on the co-localization of SNURF and SNRPN within the imprinting control region critical to Prader-Willi syndrome, evolutionary arguments would suggest that this genetic locus is a prime candidate for mutations producing the failure-to-thrive phenotype of neonates with this syndrome and of corresponding mouse models. Hence the SNURF-SNRPN gene may encode a paternally derived postnatal growth factor.     

Prader-Willi syndrome: an update and review for the primary pediatrician

Prader-Willi syndrome, the first known human genomic imprinting disorder, is one of the most common micro-deletion syndromes. Prader-Willi syndrome is caused by the absence of certain paternally inherited genes on the long arm of chromosome 15, resulting in a complete absence of the active copy of the genetic information in this region. It is most commonly known for its food-related characteristics of hyperphagia, food-seeking behavior, and consequent obesity. Primary care physicians play an important role in the care of children with Prader-Willi syndrome, from recognizing the presenting signs and symptoms at its various stages to understanding their unique medical, developmental, behavioral, and dietary issues. They can also serve as a valuable source of support and advocacy for the family. This article reviews the current state of knowledge about Prader-Willi syndrome and discusses up-to-date understanding of the management of this condition.