Unusual dysmorphic features in five patients with Noonan's syndrome: a brief review

Noonan's syndrome is a relatively common, multiple congenital anomaly syndrome, genetically inherited as an autosomal dominant disorder with variable penetrance. It is defined by a characteristic phenotype, congenital heart disease, ocular defects and mild mental retardation. Molecular studies have confirmed that it is a heterogeneous disorder and there may be evidence for an autosomal recessive mode of inheritance.1 The gene responsible for Noonan' syndrome has been mapped to the long arm of chromosome 12.2,3 The human deltex gene (DLT x 1), mapping to chromosomal region 12q24 in the vicinity of the Noonan's syndrome critical region is being evaluated as a candidate gene for this disorder.4 Various types of musculoskeletal abnormalities have been reported, including short stature, craniofacial dysmorphism, short or webbed neck and fetal pads in fingers and toes.5 We report five cases with the unusual physical features of overriding toes and simian creases. Such abnormalities can be considered among the minor manifestations of the syndrome.     

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.     

Prader-Willi syndrome in siblings,due to unbalanced translocation between chromosomes 15 and 22.

In a family in which the father carried a balanced translocation between chromosomes 15 and 22 two of his children had Prader-Willi syndrome and an unbalanced chromosome complement, having lost the proximal bands from the long arm of chromosome 15. His four other surviving children were normal but carried a balanced translocation.     

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.     

Neural misdirection in congenital ocular fibrosis syndrome: implications and pathogenesis

A child with congenital ocular fibrosis syndrome and oculocutaneous albinism displayed two distinct neural misdirection syndromes: synergistic divergence and Marcus Gunn jaw winking. This and other reported cases of misdirected innervation in patients with congenital fibrosis syndrome suggest that normal neuronal connections fail to become established early in development and that lack of innervation may underlie the pathologic features of the disorder. The prevailing concept of congenital fibrosis syndrome as a primary myopathy should be reconsidered.     

The Rieger syndrome and a chromosome 13 deletion

The Rieger syndrome, characterized by a prominent Schwalbe line, iris strands to the cornea, iris hypoplasia, dental abnormalities, facial malformations, and umbilical defects, is inherited in an autosomal dominant pattern. We studied a boy with the ocular features of the Rieger syndrome, micrognathia, and redundancy of the periumbilical skin. Chromosome analysis revealed an interstitial deletion of the long arm of chromosome 13 involving the distal region of band q14 through band q31. As there was a previous report of the Rieger syndrome in a child with an interstitial deletion of chromosome 13 (q12,q22), we suggest that a gene for this disorder may be located in the segment q14 to q22.     

Prader-Willi syndrome and mosaic Turner's syndrome

We present a female with both Prader-Willi syndrome and Turner's syndrome, a combination not previously reported. We review her clinical presentation and discuss her growth pattern, mental development, and puberty, in relation to her mosaic Turner and Prader-Willi syndromes.     

Penoscrotal inversion, hypospadias, imperforate anus, facial anomalies, and developmental delay: definition of a new clinical syndrome

 We describe a 2-month-old boy with penoscro- tal inversion, hypospadias, imperforate anus, facial anomalies, developmental retardation, and a subtelomeric deletion of chromosome 13q. His phenotype with anogenital malformations and characteristic facies closely resembled two unrelated patients with minute deletions of chromosome 13q who we reported earlier. In addition, he had unilateral renal agenesis. We propose that these patients represent a clinically recognizable, novel chromosomal microdeletion syndrome. The findings indicate the presence of a major gene(s) on chromosome 13q33.2qter that regulate(s) the migration and development of ano-reno-genital cells and organs. We speculate that mutations of this developmental gene(s) may also result in more frequent congenital malformations (isolated hypospadias, uterus bicornis, unilateral renal agenesis). Additional studies are needed to further delineate the genetic defect. Accepted: 15 September 1999     

The trisomy (5)(q31-qter) syndrome: study of a family with a t(5:14) translocation.

We report a child with multiple malformations caused by trisomy for the distal part of the long arm of chromosome No 5. A neonatal diagnosis of Down''s syndrome had previously been made on the basis of clinical examination and the detection of an additional chromosome not unlike No 21. A subsequent clinical re-evaluation, with the cooperation of the parents who permitted further studies, led to the confirmation of the true diagnosis. The mother was the carrier of a balanced translocation between chromosome No 5 and No 14. The child had severe growth and psychomotor retardation and characteristic features: microcephaly, antimongoloid slant, epicanthus, low set ears, down-turned mouth, and long upper lip. She was hypertonic and a congenital heart disease (atrial septal defect) was present. We have compared this case with others known to be trisomic for segment 5q31-qter.     

IGF-related proteins at birth in a case of antenatally diagnosed Silver-Russell syndrome

We report here a case with severe intrauterine growth restriction from the first trimester and clinical features of Silver-Russell syndrome including microcephaly, low-set ear, atrial septum defect, ventricular septum defect, diaphragmatic relaxation, and rocker bottom feet. Silver-Russell syndrome is thought to result from deletion of the distal long arm of chromosome 15 on which the IGF-I receptor (IGF-IR) gene is located. We measured both the maternal and cord blood levels of GH, IGF-I, and IGF-binding protein and performed an immunohistochemical study of IGF-IR in the placenta to investigate whether these IGF-related proteins were affected in this patient. The hormonal level of these proteins did not significantly differ from normal neonates, and immunohistochemical analysis suggested IGF-IR protein levels in the placenta were comparable to normal term neonates. These results support the hypothesis that growth insufficiency could occur in patients with monosomy of the distal long arm of chromosome 15 and suggest a critical threshold for IGF-related fetal growth in early pregnancy.     

Patchy white matter hyperintensity in ring chromosome 18 syndrome

Ring chromosome 18 syndrome is a chromosomal abnormality in which partial deletions occur at both ends of chromosome 18, that is, distally on the short and long arms. Previously reported brain magnetic resonance imaging (MRI) abnormalities include diffuse hyperintensity in the white matter, which has been regarded as hypomyelination because the gene for myelin basic protein production is located on the long arm of chromosome 18. We report the case of a 14‐year‐old boy with ring chromosome 18 syndrome, whose MRI showed patchy asymmetrical T2 and fluid‐attenuated inversion‐recovery hyperintensities in the deep white matter as well as diffuse hypomyelination. These patchy lesions may indicate demyelination or gliosis rather than hypomyelination. This result differs from previous reports.     

Clinical features and molecular genetic analysis of a boy with Prader-Willi syndrome caused by an imprinting defect

Abstract Prader-Willi syndrome (PWS) is a neuroendocrine disorder caused by a non-functioning paternally derived gene(s) within the chromosome region 15q11-q13. Most cases result from microscopically visible deletions of paternal origin, or maternal uniparental disomy of chromosome 15. In both instances no recurrence has been reported. In rare cases, PWS is associated with lack of gene expression from the paternal allele due to an imprinting defect. We report the clinical features and the molecular genetic analysis of the first Danish child with PWS due to a defect of the putative imprinting centre (IC). When the imprinting mutation is inherited from a carrier father, the risk that future children will be affected is theoretically 50%. It is therefore important that these families are referred to a geneticist for counselling and further investigation. Prenatal diagnosis is currently only feasible when the mutation has been identified in the affected child.     

A FAMILIAL 3/18 RECIPROCAL TRANSLOCATION RESULTING IN CHROMOSOME DUPLICATION-DEFICIENCY (3?+– 18q -)

Following 3 abortions a mother with 3/18 reciprocal translocation gave birth to 2 sons with multiple congenital abnormalities. Chromosome analysis in one of them revealed trisomy for a segment of one arm of chromosome No. 3 and a deletion involving the long arm of No. 18. The clinical features resembled closely those reported in deletion of the long arm of chromosome No. 18. At the age of 12 months he had normal serum levels of IgM, IgG and IgA. Both parents and the child had blood group O. Serum from the child revealed an absence of anti-A isoagglutinins, and anti-B isoagglutinins could only be detected with special technique, wheras both parents had relatively high titres of both isoagglutinins. The gene loci of MNS, Rh, Duffy, Gm, Hp, and phosphoglucomutase can be excluded from the deleted part of chromosome No. 18.     

Ophthalmologic features of Prader-Willi syndrome

Forty-six patients with Prader-Willi syndrome were examined to determine the incidence and character of ocular abnormalities. All patients met clinical criteria for this syndrome including infantile hypotonia, hypogonadism, truncal obesity, intellectual impairment, dysmorphic facies, and short stature. Thirty-two patients had best corrected visual acuities between 6/6 and 6/9 in each eye. Seven patients (15%) had myopia greater than -3.75 diopters. Nineteen (41%) patients had astigmatism of 1.25 diopters or greater. Amblyopia of strabismic, anisometropic, or ametropic etiology was present in 11 (24%) of the patients. Strabismus was present in 25 (54%) patients: 22 (48%) patients had esotropia and three (7%) had exotropia. Nine patients either received or required strabismus surgery. Thirty-three percent of the patients examined for iris transillumination defects had this finding. This study represents the first large series of patients with Prader-Willi syndrome to undergo detailed ophthalmologic evaluation. Recognition of this syndrome is important because of the high incidence of potentially treatable ocular problems.     

四例Prader-Willi综合征患儿的分子遗传缺陷分析

目的 观察Pradet-Willi综合征(PWS)患者的分子遗传基础及临床筛查策略,为进一步的遗传咨询提供信息。方法 应用甲基化特异性PCR(MSPCR)及荧光原位杂交(FISH)技术对4例临床诊断PWS患者进行基因分析研究。结果 4例患者MSPCR结果均显示缺乏父源的相关片段,而仅为母源DNA,即第15号染色体母源单亲二体(matUPD15);FISH检测发现2例15q近端SNRPN基因片段的微小缺失。结论 父源15q11-13特异区带缺失及matUPD15亦与我国PWS患者致病的分子病理缺陷有关。临床开展相关的细胞分子遗传学实验诊断对PWS临床诊断及遗传咨询、产前诊断都具有积极的作用。     

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.     

Molecular analysis of patients with Wiedemann-Beckwith syndrome I. Gene dosage on the short arm of chromosome 11

Wiedemann-Beckwith syndrome (WBS) is characterised by a specific group of congenital malformations associated with an increased concurrent risk for development of a defined group of childhood neoplasms. The mode of inheritance is complex, but recently compiled family data suggest that it is an autosomal dominant trait of varying expression. It has previously been suggested that major rearrangements on the short arm of chromosome 11 may be involved in the aetiology of the disease, particularly in the region of the insulin like growth factor II (IGF-II) gene (11p15.5). This gene is thought to be parentally imprinted in the mouse and it has been suggested that in the human, duplication of the non-imprinted locus in WBS patient might lead to diploid expression of the gene and consequent general hyperplasia. This model predicts that there should be both frequent and parental origin specific duplication of the IGF-II gene in the patients. It was the aim of this study to examine the IGF-II locus and its surrounding chromosomal environment for such lesions in a large number of WBS patients. Using restriction fragment length polymorphism analysis for four linked markers on 11p and genomic clones internal to the IGF-II locus we could find no evidence of alteration or amplification of this area in any of the 11 patients investigated. In one patient who developed a Wilms tumour we could find no evidence for loss of any material on the short arm of chromosome 11 as reported previously. We conclude that amplification of genes on the short arm of chromosome 11 is not a frequent occurrence in WBS and certainly not a prerequisite, leaving open the possibility that mutations in unknown transacting factors might affect the expression of IGF-II in these patients in the absence of lesions in the gene itself.     

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.     

Contiguous Gene Syndromes as Multiple Anomalies Syndromes: Molecular Basis and Approach to Gene Cloning

Recent knowledge on molecular basis of several contiguous gene syndromes as multiple anomalies syndromes, such as Prader-Willi syndrome (PWS), Angelman syndrome (AS), Beckwith-Wiedemann syndrome (BWS), tricho-rhino-phalageal syndrome types I (TRPS I) and II (TRPS II or LGS), and complex glycerol kinase deficiency (CGKD), are reviewed. Based on the results of DNA deletion studies and on the evidence for the genomic imprinting mechanism of both PWS and AS, a model for the occurrence of the two syndromes is proposed. Also, a strategy of the microdissection/microcloning technique as a reverse genetics technique, i. e., direct cloning of chromosomal DNAs from a defined region of human chromosome, particularly for the cloning of the exostosis gene in TRPS, is presented.