Deletions of proximal 15q and non-classical Prader-Willi syndrome phenotypes

The Mandibular and Hyoid Arches-From Molecular Patterning to Shaping Bone and Cartilage

The mandibular and hyoid arches collectively make up the facial skeleton, also known as the viscerocranium. Although all three germ layers come together to assemble the pharyngeal arches, the majority of tissue within viscerocranial skeletal components differentiates from the neural crest. Since nearly one third of all birth defects in humans affect the craniofacial region, it is important to understand how signalling pathways and transcription factors govern the embryogenesis and skeletogenesis of the viscerocranium. This review focuses on mouse and zebrafish models of craniofacial development. We highlight gene regulatory networks directing the patterning and osteochondrogenesis of the mandibular and hyoid arches that are actually conserved among all gnathostomes. The first part of this review describes the anatomy and development of mandibular and hyoid arches in both species. The second part analyses cell signalling and transcription factors that ensure the specificity of individual structures along the anatomical axes. The third part discusses the genes and molecules that control the formation of bone and cartilage within mandibular and hyoid arches and how dysregulation of molecular signalling influences the development of skeletal components of the viscerocranium. In conclusion, we notice that mandibular malformations in humans and mice often co-occur with hyoid malformations and pinpoint the similar molecular machinery controlling the development of mandibular and hyoid arches.

Expanded Prader-Willi Syndrome due to an Unbalanced de novo Translocation t(14;15): Report and Review of the Literature

In the present study, we report a case of a female infant with a de novo unbalanced t(14;15) translocation resulting in a 14-Mb deletion of the 15q11.1q14 region. The deletion includes the 15q11.2q13 Prader-Willi syndrome (PWS) critical region, while no known deleted genes are found in the 14qter region. According to literature review, patients with similar or larger deletions in the 15q region exhibit an expanded phenotype of PWS with case-specific atypical features such as severe retardation, absence of speech, microcephaly, retrognathia, bifid uvula, ear malformations, and heart defects in addition to typical features of PWS. Our proband exhibited increased deep tendon reflexes, an atypical feature which is not reported in the reviewed literature. The severity of the phenotype is not directly associated with the size of the deletion; however, using a combination of methods, the identification of breakpoints and the deleted genes can be helpful for the prognostication in patients with atypical PWS deletions.

Atypical Prader-Willi and 15q13.3 Microdeletion Syndromes in a Patient with an Unbalanced Translocation

Prader-Willi syndrome (PWS) and recurrent 15q13.3 microdeletion syndrome can be caused by genomic rearrangements in the complex 15q11q13 chromosomal region. Here, we describe the first female child with PWS and 15q13.3 microdeletion syndrome resulting from an unusual 10.7-Mb deletion from 15pter to 15q13.3 due to an unbalanced de novo 15;19 translocation. The patient presents with hypotonia, microcephaly, developmental delay with lack of speech, intellectual disability, happy demeanor, clinodactyly of the 4th and 5th fingers, and dysmorphic facial features discordant for PWS and consistent with an atypical phenotype.

A case of an atypically large proximal 15q deletion as cause for Prader-Willi syndrome arising from a de novo unbalanced translocation

We describe an 11 month old female with Prader-Willi syndrome (PWS) resulting from an atypically large deletion of proximal 15q due to a de novo 3;15 unbalanced translocation. The 10.6 Mb deletion extends from the chromosome 15 short arm and is not situated in a region previously reported as a common distal breakpoint for unbalanced translocations. There was no deletion of the reciprocal chromosome 3q subtelomeric region detected by either chromosomal microarray or FISH. The patient has hypotonia, failure to thrive, and typical dysmorphic facial features for PWS. The patient also has profound global developmental delay consistent with an expanded, more severe, phenotype.

Expanded Prader-Willi syndrome due to chromosome 15q11.2-14 deletion: report and a review of literature

We report on a male infant with de novo unbalanced t(5;15) translocation resulting in a 17.23 Mb deletion within 15q11.2-q14 and a 25.12 kb deletion in 5pter. The 15q11.2-q14 deletion encompassed the 15q11.2-q13 Prader-Willi syndrome (PWS) critical region and the recently described 15q13.3 microdeletion syndrome region while the 5pter deletion contained no RefSeq genes. From our literature review, patients with similar deletions in chromosome 15q exhibit expanded phenotype of severe developmental delay, protracted feeding problem, absent speech, central visual impairment, congenital malformations and epilepsy in addition to those typical of PWS. The patient reported herein had previously unreported anomalies of mega cisterna magna, horseshoe kidney and the rare neonatal interstitial lung disease known as pulmonary interstitial glycogenosis. Precise breakpoint delineation by microarray is useful in patients with atypical PWS deletions to guide investigation and prognostication.

Review and update of SPRED1 mutations causing Legius syndrome

Legius syndrome presents as a mild neurofibromatosis type 1 (NF1) phenotype. Multiple café-au-lait spots and macrocephaly are present with or without axillary or inguinal freckling. Other typical NF1-associated features (Lisch nodules, bone abnormalities, neurofibromas, optic pathway gliomas, and malignant peripheral nerve sheath tumors) are systematically absent. Legius syndrome is caused by germline loss-of-function SPRED1 mutations, resulting in overactivation of the RAS-MAPK signal transduction cascade. The first families were identified in 2007. Here, we review all identified SPRED1 mutations and summarize molecular, clinical, and functional data. All mutations have been deposited in a database created using the Leiden Open Variation Database software and accessible at http://www.lovd.nl/SPRED1. At present, the database contains 89 different mutations identified in 146 unrelated probands, including 16 new variants described for the first time. The database contains a spectrum of mutations: 29 missense, 28 frameshift, 19 nonsense, eight copy number changes, two splicing, one silent, one in-frame deletion and a mutation affecting the initiation codon. Sixty-three mutations and deletions are definitely pathogenic or most likely pathogenic, eight SPRED1 mutations are probably benign rare variants, and 17 SPRED1 missense mutations are still unclassified and need further family and functional studies to help with the interpretation.

Identification of SPRED1 deletions using RT-PCR, multiplex ligation-dependent probe amplification and quantitative PCR

Legius syndrome, is a recently identified autosomal dominant disorder caused by loss of function mutations in the SPRED1 gene, with individuals mainly presenting with multiple café-au-lait macules (CALM), freckling and macrocephaly. So far, only SPRED1 point mutations have been identified as the cause of this syndrome. To determine if copy number changes (CNCs) are a cause of Legius syndrome, we have used a Multiplex Ligation-dependent Probe Amplification (MLPA) assay covering all SPRED1 exons in a cohort of 510 NF1-negative patients presenting with multiple CALMs with or without freckling, but no other NF1 diagnostic signs. Four different deletions were identified by MLPA and confirmed by quantitative PCR, reverse transcriptase PCR and/or array CGH: a deletion of exon 1 and the SPRED1 promoter region in a proband and two first-degree relatives; a deletion of the entire SPRED1 gene in a sporadic patient; a deletion of exon 2-6 in a proband and her father; and an ∼6.6 Mb deletion on chromosome 15 that spans SPRED1 in a sporadic patient. Deletions account for ∼10% of the 40 detected SPRED1 mutations in this cohort of 510 individuals. These results indicate the need for dosage analysis to complement sequencing-based SPRED1 mutation analyses.

Complex chromosome rearrangements related 15q14 microdeletion plays a relevant role in phenotype expression and delineates a novel recurrent syndrome

Complex chromosome rearrangements are constitutional structural rearrangements involving three or more chromosomes or having more than two breakpoints. These are rarely seen in the general population but their frequency should be much higher due to balanced states with no phenotypic presentation. These abnormalities preferentially occur de novo during spermatogenesis and are transmitted in families through oogenesis.Here, we report a de novo complex chromosome rearrangement that interests eight chromosomes in eighteen-year-old boy with an abnormal phenotype consisting in moderate developmental delay, cleft palate, and facial dysmorphisms.Standard G-banding revealed four apparently balanced translocations [corrected] involving the chromosomes 1;13, 3;19, 9;15 and 14;18 that appeared to be reciprocal. Array-based comparative genomic hybridization analysis showed no imbalances at all the breakpoints observed except for an interstitial microdeletion on chromosome 15. This deletion is 1.6 Mb in size and is located at chromosome band 15q14, distal to the Prader-Willi/Angelman region. Comparing the features of our patient with published reports of patients with 15q14 deletion this finding corresponds to the smallest genomic region of overlap. The deleted segment at 15q14 was investigated for gene content.

De novo interstitial duplication of the 15q11.2-q14 PWS/AS region of maternal origin: Clinical description, array CGH analysis, and review of the literature

The 15q11-q13 PWS/AS critical region involves genes that are characterized by genomic imprinting. Multiple repeat elements within the region mediate rearrangements, including interstitial duplications, interstitial triplications, and supernumerary isodicentric marker chromosomes, as well as the deletions that cause Prader-Willi syndrome (PWS) and Angelman syndrome (AS). Recently, duplications of maternal origin concerning the same critical region have been implicated in autism spectrum disorders (ASD). We present a 6-month-old girl carrying a de novo duplication of maternal origin of the 15q11.2-q14 PWS/AS region (17.73 Mb in size) [46,XX,dup(15)(q11.2-q14)] detected with a high-resolution microarray-based comparative genomic hybridization (array-CGH). The patient is characterized by severe hypotonia, obesity, microstomia, long eyelashes, hirsutism, microretrognathia, short nose, severe psychomotor retardation, and multiple episodes of drug-resistant epileptic seizures, while her brain magnetic resonance imaging (MRI) documented partial corpus callosum dysplasia. In our patient the duplicated region is quite large extending beyond the Prader-Willi-Angelman critical region (PWACR), containing a number of genes that have been shown to be involved in ASD, exhibiting a severe phenotype, beyond the typical PWS/AS clinical manifestations. Reporting of similar well-characterized clinical cases with clearly delineated breakpoints of the duplicated region will clarify the contribution of specific genes to the phenotype.

An interstitial 15q11-q14 deletion: expanded Prader-Willi syndrome phenotype

We present an infant girl with a de novo interstitial deletion of the chromosome 15q11-q14 region, larger than the typical deletion seen in Prader-Willi syndrome (PWS). She presented with features seen in PWS including hypotonia, a poor suck, feeding problems, and mild micrognathia. She also presented with features not typically seen in PWS such as preauricular ear tags, a high-arched palate, edematous feet, coarctation of the aorta, a PDA, and a bicuspid aortic valve. G-banded chromosome analysis showed a large de novo deletion of the proximal long arm of chromosome 15 confirmed using FISH probes (D15511 and GABRB3). Methylation testing was abnormal and consistent with the diagnosis of PWS. Because of the large appearing deletion by karyotype analysis, an array comparative genomic hybridization (aCGH) was performed. A 12.3 Mb deletion was found which involved the 15q11-q14 region containing approximately 60 protein coding genes. This rare deletion was approximately twice the size of the typical deletion seen in PWS and involved the proximal breakpoint BP1 and the distal breakpoint was located in the 15q14 band between previously recognized breakpoints BP5 and BP6. The deletion extended slightly distal to the AVEN gene including the neighboring CHRM5 gene. There is no evidence that the genes in the 15q14 band are imprinted; therefore, their potential contribution in this patient's expanded PWS phenotype must be a consequence of dosage sensitivity of the genes or due to altered expression of intact neighboring genes from a position effect.

Trisomy 9p and Prader-Willi syndromes in an infant resulting from a de-novo unbalanced t(9;15) translocation

Trisomy 9p is a well-described dysmorphic syndrome. The physical features include hypertelorism, down-slanting palpebral fissures, deep-set eyes, down-turned corners of the mouth, and mild skeletal anomalies including hypoplastic terminal phalanges. We report an infant born with some of the typical features of trisomy 9p syndrome, as well as additional features that include extreme joint hyperlaxity with subluxation of the knees and elbows, arachnodactyly, and total anomalous pulmonary venous return. The karyotype revealed an unbalanced chromosome complement. Specifically, a derivative chromosome from a de-novo unbalanced translocation of chromosomes 9 and 15 resulted in partial trisomy of 9pter to 9q13 and deletion of the long arm of chromosome 15 proximal to band q13. Fluorescence in-situ hybridization studies and methylation analysis by Southern blotting revealed deletion of the SNRPN locus on the paternally derived chromosome 15, consistent with Prader-Willi syndrome. This infant represents the first reported case of trisomy 9p syndrome with total anomalous pulmonary venous return and hypoplasia of the amygdala and hippocampus, with the additional finding of Prader-Willi syndrome resulting from a derivative chromosome arising from an unbalanced de-novo t(9;15) translocation.

Recurrent rearrangements in the proximal 15q11–q14 region: a new breakpoint cluster specific to unbalanced translocations

Unbalanced translocations, that involve the proximal chromosome 15 long arm and the telomeric region of a partner chromosome, result in a karyotype of 45 chromosomes with monosomy of the proximal 15q imprinted region. Here, we present our analysis of eight such unbalanced translocations that, depending on the parental origin of the rearranged chromosome, were associated with either Prader-Willi or Angelman syndrome. First, using FISH with specific BAC clones, we characterized the chromosome 15 breakpoint of each translocation and demonstrate that four of them are clustered in a small 460 kb interval located in the proximal 15q14 band. Second, analyzing the sequence of this region, we demonstrate the proximity of a low-copy repeat 15 (LCR15)-duplicon element that is known to facilitate recombination events at meiosis and to promote rearrangements. The presence, in this region, of both a cluster of translocation breakpoints and a LCR15-duplicon element defines a new breakpoint cluster (BP6), which, to our knowledge, is the most distal breakpoint cluster described in proximal 15q. Third, we demonstrate that the breakpoints for other rearrangements including large inv dup (15) chromosomes do not map to BP6, suggesting that it is specific to translocations. Finally, the translocation breakpoints located within BP6 result in very large proximal 15q deletions providing new informative genotype-phenotype correlations.

Characterization of a 5.3 Mb deletion in 15q14 by comparative genomic hybridization using a whole genome “tiling path” BAC array in a girl with heart defect, cleft palate, and developmental delay

High-resolution array CGH utilizing sets of overlapping BAC and PAC clones ("tiling path") covering the whole genome is a powerful novel tool for fast detection of submicroscopic chromosome deletions or duplications. We describe the successful application of a submegabase resolution whole genome "tiling path" BAC array to confirm and characterize a de novo interstitial deletion of chromosome 15. The deletion has a size of 5.3 Mb and is located within chromosome band 15q14, distal to the Prader-Willi/Angelman region. The affected girl had a heart defect, cleft palate, recurrent infections, and developmental delay. In contrast to GTG banding, array CGH determined the exact number of deleted genes and thus allowed the identification of candidate genes for cleft palate (GREM1, CX36, MEIS2), congenital heart defect (ACTC, GREM1, CX36, MEIS2), and mental retardation (ARHGAP11A, CHRNA7, CHRM5).

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 characterization of a unique de novo 15q deletion associated with Prader-Willi syndrome and central visual impairment

We report a 2-year-old boy with Prader-Willi Syndrome (PWS) caused by a deletion of the PWS critical region as a result of an unbalanced translocation t(3;15). Additional features, including central visual impairment, relative macrocephaly, retrognathia, preauricular tags, and bilateral club-feet, were noticed. The extension of the deletion was determined by fluorescence in situ hybridization (FISH) analysis using 11 region-specific YAC clones. Nine YACs were found to be deleted, allowing us to determine that the deletion is larger than in patients with typical PWS deletions. The karyotype of this patient can thus be designated: 45,XY,-15,der(3)t(3;15)(qter;q14).ish der(3)t(3;15)(qter;q14) (wcp3+,wcp15+,D15S10-,PML+,D15Z1-,D3S4560+,801_f_9x1, 815_e_6x2) de novo. Molecular analyses using seven polymorphic markers helped to narrow down the breakpoint between marker ACTC.PC3 and the distal end of the YAC 815_e_6. These results provide evidence that haploinsufficiency for genes in 15q13-q14, not affected in common PWS deletions, is associated with the additional features found in the patient, including a central visual impairment.

GABA-A receptor beta3 and alpha5 subunit gene cluster on chromosome 15q11-q13 and bipolar disorder: a genetic association study

There is accumulated evidence that the genes coding for the receptor of gamma aminobutyric acid (GABA), the most important inhibitory neurotransmitter in the CNS, may be involved in the pathogenesis of affective disorders. In a previous study, we have found a genetic association between the GABA-A receptor alpha5 subunit gene locus (GABRA5) on chromosome 15q11-of 13 and bipolar affective disorder. The aim of the present study was to examine the same subjects to see if there exists a genetic association between bipolar affective disorder and the GABA receptor beta3 subunit gene (GABRB3), which is located within 100 kb from GABRA5. The sample consisted of 48 bipolar patients compared to 44 controls (blood donors). All subjects were Greek, unrelated, and personally interviewed. Diagnosis was based on DSM-IV and ICD-10 criteria. The marker used was a dinucleotide (CA) repeat polymorphism with 12 alleles 179 to 201 bp long; genotyping was successful in all patients and 43 controls. The distribution of GABRB3 genotypes among the controls did not deviate significantly from the Hardy-Weinberg equilibrium. No differences in allelic frequencies between bipolar patients and controls were found for GABRB3, while this locus and GABRA5 did not seem to be in significant linkage disequilibrium. In conclusion, the GABRB3 CA-repeat polymorphism we investigated does not present the observed association between bipolar affective illness and GABRA5. This could be due to higher mutation rate in the GABRB3 CA-repeat polymorphism, but it might also signify that GABRA5 is the gene actually associated with the disease.

Cytogenetic and molecular cytogenetic studies of a case of interstitial deletion of proximal 15q

A 4-month-old child with multiple anomalies was determined to have an interstitial deletion of chromosome 15, i.e., del(15) (q12q14). The deletion appears not to be a typical deletion of 15q12 such as seen in Angelman and Prader-Willi syndromes, but appears to be more distal, involving either loss of all of 15q12 and part of 15q14, or part of 15q12 and most of 15q14. In either case, 15q13 is missing. Fluorescent in situ hybridization with probes for 15 centromere (D15Z), pericentromeric satellite sequences (D15Z1), and chromosome 15 painting probes shows the deleted chromosome to involve only 15 and no other acrocentric chromosome. Hybridization with probes for the AS and PWS loci (D15S11 and GABAB3, Oncor) show both sites to be intact in the deleted 15. The case is compared with two other reports with overlapping interstitial deletions of proximal 15q, neither of which shows typical features of Angelman or Prader-Willi syndromes.

A variety of genetic mechanisms are associated with the Prader-Willi syndrome

An extensive set of chromosome 15 DNA polymorphisms and densitometric analysis with four markers mapping to the Prader-Willi chromosome region (PWCR) of chromosome 15 have been used to characterize a cohort of 30 subjects with classical Prader-Willi syndrome (PWS). Molecular analysis enabled the classification of the PWS subjects into four groups: (A) 18 subjects (60%) had deletions of paternal 15q11-13 involving a common set of DNA markers. Two subjects had differently sized deletions, one larger and one smaller than the other cases. (B) Eight (27%) had maternal uniparental disomy for chromosome 15. (C) One (3%) had a marker chromosome carrying an extra copy of the PWCR. The marker chromosome was demonstrated to be of paternal origin and the two intact chromosomes were maternally derived. This case represents an apparent exception to the generally held view that PWS is associated with an absence of paternally inherited gene(s) located in the PWCR. (D) The remaining three cases (10%) had none of the above abnormalities. This last subgroup of patients has not previously been well characterized but could represent limited deletions not detectable with the markers used or abnormalities in the imprinting process. These cases represent potentially valuable resources to elucidate more precisely the fundamental disorders responsible for PWS.

Evaluation of potential models for imprinted and nonimprinted components of human chromosome 15q11-q13 syndromes by fine-structure homology mapping in the mouse

Prader-Willi and Angelman syndromes are complex neurobehavioral contiguous gene syndromes whose expression depends on the unmasking of genomic imprinting for different genetic loci in human chromosome 15q11-q13. The homologous chromosomal region in the mouse genome has been fine-mapped by using interspecific (Mus spretus) crosses and overlapping, radiation-induced deletions to evaluate potential animal models for both imprinted and nonimprinted components of these syndromes. Four evolutionarily conserved sequences from human 15q11-q13, including two cDNAs from fetal brain (DN10, D15S12h; DN34, D15S9h-1), a microdissected clone (MN7; D15F37S1h) expressed in mouse brain, and the gene for the beta 3 subunit of the gamma-aminobutyric acid type A receptor (Gabrb3), were mapped in mouse chromosome 7 by analysis of deletions at the pink-eyed dilution (p) locus. Three of these loci are deleted in pre- and postnatally lethal p-locus mutations, which extend up to 5.5 +/- 1.7 centimorgans (cM) proximal to p; D15S9h-1, which maps 1.1 +/- 0.8 cM distal to p and is the mouse homolog of the human gene D15S9 (which shows a DNA methylation imprint), is not deleted in any of the p-locus deletion series. A transcript from the Gabrb3 gene, but not the transcript detected by MN7 at the D15F37S1h locus, is expressed in mice homozygous for the p6H deletion, which have an abnormal neurological phenotype. Furthermore, the Gabrb3 transcript is expressed equally well from the maternal or paternal chromosome 7 and, therefore, its expression is not imprinted in mouse brain. Deletions at the mouse p locus should serve as intermediate genetic reagents and models with which to analyze the genetics and etiology of individual components of human 15q11-q13 disorders.

Differentiated recurrence risk estimations in the Prader-Willi syndrome

The Prader-Willi syndrome usually occurs sporadically. About 60% of the patients show a chromosomal deletion of proximal 15q. There are only a few reports on familial recurrence. Two previous estimates give either a low but recognizable recurrence risk of 1.6% or a risk of less than 0.1%. The inconsistency is obviously due to differences in the stringency of the diagnostic criteria used and to different modes of ascertainment of cases. This gave rise to a review of the literature, leading to the following suggestions: (1) A deletion at 15q has not been found in a familial case of PWS, except in those cases where del(15q) is due to familial structural chromosome rearrangements. Hence, with de novo deletion, the recurrence risk should be nearly zero. (2) In cases with familial translocation, risk estimates depend on the variable nature of the familial chromosome mutation. (3) If only one child is affected and has no deletion at 15q, this may be a sporadic or an isolated familial case. For this situation I estimated an overall recurrence risk of 0.4%. (4) If two or more sibs are affected, I consider a risk of 50% that the next sib may also be affected. This estimate reflects the observed segregation ratio and is in accordance with the proposed genomic imprinting model in the etiology of PWS. Prenatal cytogenetic diagnosis in a pregnancy at risk for PWS is hampered since del(15q) is almost exclusively found in sporadic cases. Hence, this method is limited to those very rare cases where del(15q) is due to familial structural chromosome rearrangements.(ABSTRACT TRUNCATED AT 250 WORDS)

Interstitial 15q deletion without a classic Prader-Willi phenotype

We report on a newborn boy with pronounced hypotonia, cryptorchidism, minor facial anomalies, congenital heart defect, neurologic anomaly, deafness, renal anomaly, and bifid uvula. The patient has a de novo proximal interstitial deletion of chromosome 15 reaching to band q14, larger than that usually seen in Prader-Willi and Angelman syndromes.

Diagnosis of Angelman syndrome in infants

The diagnosis of Angelman syndrome (AS) has seldom been made in infants because the previously described characteristic manifestations usually are not apparent until after age 2 years. We describe 4 AS patients, one of whom has oculocutaneous albinism, who were less than 2 years old when first evaluated. All 4 have deletions of the region q11.2-q13 of chromosome 15. In the 3 cases in which parents were available for study the deleted chromosome 15 was maternally derived, as determined by cytological markers. All of the patients presented with severe to profound global developmental delay and postnatal-onset microcephaly; they had seizures, hypotonia, hyperreflexia, and hyperkinesis. All were hypopigmented as compared to their relatives. Each had eye abnormalities; all had choroidal pigment hypoplasia. None were initially described as having an abnormal appearance. We believe that AS is far more common than previously thought and present these 4 children to emphasize the manifestations that may be helpful in making the diagnosis in the young patient. We also emphasize the hypopigmentation that patients with AS frequently have, including what we think is the first reported case of albinism and AS.

Rearrangement of chromosome 15 in the region q11.2----q12 in an individual with obesity syndrome and her normal mother

Rearrangement of the proximal long arm of chromosome 15 have been found in most patients with the Prader-Willi syndrome (PWS) and in some with Angelman syndrome. We present an individual with syndromic obesity and her normal mother, who both have an abnormal chromosome 15. The proposita is a 26-year-old women with marked obesity, acanthosis, nigricans, short fingers, and severe cone degeneration of the retina. She has high plasma insulin levels, hypothyroidism, and an empty sella on CT scan. High-resolution chromosome banding demonstrated an increase in band 15q12. Further analysis showed the same abnormal 15 in her normal mother but not in her normal sister. This case and recent reports in the literature indicate that duplication of chromosome 15q in the PWS region may be associated with a syndrome of obesity, acanthosis nigricans, empty sella, and rodcore dystrophy as well as with a normal phenotype. Whether normal individuals with such a duplication carry increased risk of having offspring with an obesity syndrome is yet to be determined.

Congenital cardiovascular malformations (CCVM) and structural chromosome abnormalities: a report of 9 cases and literature review

Nine cases of congenital cardiovascular malformations (CCVM) with associated unbalanced structural chromosomal abnormalities were ascertained in a population-based study of heart defects, constituting 0.4% of the 2,103 cases of CCVM in the Baltimore-Washington Infant Study (BWIS). This represents a four-fold increase over the general population rate. In an effort to determine possible phenotype/karyotype correlations, the literature was searched for cases with similar karyotypic abnormalities. This comparison of 223 literature cases of karyotypic abnormalities with nine similar cases ascertained by heart malformation has provided the opportunity to review cardiac defects reported in cases of structural abnormalities of chromosomes 1, 3, 7, 8, 9, 10, 11, 15, and 18. The most common cardiac malformation present in the chromosomal cases was ventricular septal defect (VSD) (39%); similarly VSD is the most common CCVM among children with heart defects, although it is the primary defect in only 20% of the BWIS cases. Among all heart defects in the BWIS, atrial septal defect (ASD) represents 5.5% of all cases, but in cases of 8p duplication, ASD is present in 41%. In addition, 40% of cases of 9p duplication had an ASD. Similarly, 35% of cases of 11q duplication had an ASD. While the suggestion of specific karyotype/phenotype association is premature, information on additional cases might clarify the possibility that genetic determinants related to septum formation may reside on chromosome 8, 9, and/or 11. The variety of chromosomal abnormalities in cases with ventricular septal defect indicates one type of genetic heterogeneity that may be involved in this very common heart defect.

Prenatal diagnosis of del(15)(q11q13)

A case of del(15)(q11q13) was detected in amniotic fluid cell cultures and confirmed by cordocentesis in a 27-year-old woman with a low maternal serum alpha-fetoprotein level. The fetus was shown to have a short femoral length on ultrasonography. This structural chromosome abnormality associated with the prenatal ultrasonographic findings and the morphological characteristics visualized after termination of pregnancy strongly suggest Prader-Willi syndrome.

The speech and language characteristics of children with Prader-Willi syndrome

Prader-Willi syndrome was initially identified in 1956. Since then, a majority of the literature pertaining to Prader-Willi has focused on the medical and genetic aspects of the syndrome. There has been limited information available regarding the speech and language abilities of children with Prader-Willi. This study investigated the communicative development of 18 children with the syndrome, ranging in age from 8:8 to 17:1. A number of evaluative procedures were used to evaluate the subjects' spontaneous speech, articulation, and receptive and expressive language abilities, as well as their voice, fluency, oral mechanisms, hearing, and their developmental histories. A variety of communicative deficiencies were found in the children's speech, language, voice, and fluency.

Prader-Willi syndrome: current understanding of cause and diagnosis

Prader-Willi syndrome (PWS) is characterized by hypotonia, obesity, hypogonadism, short stature, small hands and feet, mental deficiency, a characteristic face, and an interstitial deletion of the proximal long arm of chromosome 15 in about one-half of the patients. The incidence is estimated to be about 1 in 25,000, and PWS is the most common syndromal cause of human obesity. DNA abnormalities, usually deletions or duplications of chromosome 15, have been identified in individuals with PWS with or without recognizable chromosome 15 deletions. Paternal origin of the chromosome 15 deletion by cytogenetic and DNA studies has been found in nearly all PWS individuals studied. No cytogenetic evidence for chromosome breakage has been identified, although an environmental cause (e.g., paternal hydrocarbon-exposed occupations) of the chromosome 15 abnormality has been proposed. PWS patients with the chromosome 15 deletion are more prone to hypopigmentation compared with PWS individuals with normal chromosomes, but no other clinical differences are consistently identified between those with and without the chromosome deletion. Anthropometric, dermatoglyphic, and other clinical findings indicate homogeneity of PWS patients with the chromosome deletion and heterogeneity of the nondeletion patients. A review of our current understanding of the major clinical, cytogenetic, and DNA findings is presented, and clinical manifestations and cytogenetic abnormalities are summarized from the literature.

Proximal 15q variant as possible pitfall in the cytogenetic diagnosis of Prader-Willi syndrome

A patient with Prader-Willi syndrome showed an elongated proximal 15q, and thus was initially considered to be negative for a proximal 15q deletion. However, repeated high resolution chromosome study demonstrating the DNA-replication banding patterns revealed an obvious deletion/deficiency of the 15q12 equivalent band on that elongated chromosome 15. This deletion was further verified by comparison with the parental chromosomes 15 and the deleted chromosome 15 was of paternal origin. The elongation was due to a long variant of 15q11.2 band, which has previously been shown to be polymorphic/variable. This variable proximal 15q site could potentially mask a deletion if it is too long, or mimic a deletion if it is too short. The use of the DNA-replication banding technique instead of the more widely used trypsin banding technique could alleviate this possible pitfall.

Quantitative calibration and use of DNA probes for investigating chromosome abnormalities in the Prader-Willi syndrome

Ten genomic DNA probes, subcloned from inserts derived from a phage library constructed from the DNA of flow-sorted chromosomes, have now been mapped to locations within 15q11-15q13. By dosage blotting and densitometry, 5 of these probes map to the 15q11.2-15q12 segment missing in one 15 chromosome of a Prader-Willi syndrome (PWS) patient with a prominent cytological deletion. A sixth probe most likely maps to the same region. The other 4 probes map outside of this segment but within 15q11-15q13. Several of the 15q11.2-15q12 probes, and a cDNA probe homologous to one, have been used to test the DNA from 8 patients exhibiting a wide range of the clinical manifestations expected for PWS patients. DNA deletion was observed in all 3 patients with cytological 15q1 deletions as well as in a patient with an unbalanced (Y;15) translocation. DNA from 1 PWS patient with an unbalanced (5;15) translocation and an inverted duplication of the short arm and proximal long arm of 15 showed at least 1 and possibly 2 extra copies of each genomic probe tested. In the other 3 patients with no cytological deletions, no DNA deletions were found. Thus, the molecular probes described can be used in most PWS patients to analyze the region of proximal 15q implicated in this syndrome.

Restriction fragment length polymorphisms within proximal 15q and their use in molecular cytogenetics and the Prader-Willi syndrome

Restriction fragment length polymorphisms (RFLPs) are described in detail for 6 DNA probes (D15S9-13, D15S18) that localize to the proximal long arm of human chromosome 15 (15q11-15q13: this report and Tantravahi et al., Am. J. Med. Genet. 33:78-87. Multiple RFLPs are detected by the probe that identifies locus D15S13, and these RFLPs are shown by genomic mapping to result from a nearby insertion or deletion of 1.8 kilobases (kb) of DNA. This set of RFLPs detected by proximal 15q probes can be used for studies on the Prader-Willi syndrome (PWS) and on mentally retarded individuals with a supernumerary inv dup(15) chromosome. Five of the polymorphic loci (D15S9-13) map to the region implicated in the cause of the PWS (15q11.2-15q12). Each of 4 families tested with these probes, as well as an additional "PWS-like" patient, was informative by RFLP analysis. The two PWS deletions studied, which occurred de novo, were inherited from the chromosome 15 provided by the father. By contrast, the 2 inv dup(15) chromosomes analyzed were of maternal origin. The use of RFLPs can also simplify the molecular determination of copy number in chromosomal aneuploidy, as exemplified by analysis of individuals with the PWS and a deletion, patients with an inv dup(15), and one patient with a more complex rearrangement involving chromosome 15. Our studies demonstrate the application of DNA probes for both molecular cytogenetic studies on this chromosome region and the development of diagnostic molecular markers to aid early clinical diagnosis of the PWS.

Perinatal and first year follow-up of patients with Prader-Willi syndrome: normal size of hands and feet

Four patients with Prader-Willi syndrome, diagnosed in the neonatal period and followed during the first year of life, are reported. There were three males and one female. All four patients presented with hypotonia and distinct craniofacial dysmorphism. Prometaphase chromosome analysis showed interstitial deletion of 15q in all of them. The placentae and umbilical cords were examined in three of the patients and found normal. Electromyography done in the neonatal period suggested primary myopathy. Height, weight and head circumference were normal at birth in all patients. Hand and foot measurements showed normal size at birth and during the first year of life.

A survey of 22 individuals with Prader-Willi syndrome in New South Wales

Twenty-two individuals with Prader-Willi Syndrome in New South Wales were surveyed. The results show that males were diagnosed at a significantly earlier age than females and suggest a recent trend towards earlier diagnosis. The advantages of early diagnosis are discussed. In those in whom cytogenetic studies had been performed, 47% were found to have a deletion involving chromosome 15q11-13. Profound neonatal hypotonia had been present in all cases. Obesity became apparent between 1.5 and 10 years (mean = 3.8 years). Facial dysmorphism was reported in 83% and acromicria in 100%. Sixty-two per cent of subjects were regarded as less pigmented than first degree relatives. Cognitive assessments were performed on nine subjects. Two (22%) were functioning in the normal range of intelligence. Behaviour problems, both food-related and non-food-related, were present in the majority and placed considerable stress on the family caring for the individual with Prader-Willi Syndrome.

Similar molecular deletions on chromosome 15q11.2 are encountered in both the Prader-Willi and Angelman syndromes

Comparative molecular analysis of chromosome 15, sub-band q11.2 of patients with the Prader-Willi or Angelman syndromes demonstrates that they have a similar deletion. An hypothesis is presented that attempts to explain the tremendous degree of clinical heterogeneity in these diverse deletion-associated syndromes based on abnormal haplotypes present on the cytogenetically normal homolog. This hypothesis also addresses genetic similarities between patients who have deletion and those who have the inv dup(15) by postulating that these syndromes are caused by relative dosage ratios of normal versus abnormal alleles.

A genetic-diagnostic survey in an institutionalized population of 158 mentally retarded patients. The Viaene experience

In this report we summarize the results of a genetic-diagnostic survey of an institutionalized population of 158 severely mentally retarded patients. The etiological study was based on a clinical genetic approach with special attention to dysmorphology and neurological findings. In 72 patients a constitutional cause of their mental impairment was found: a chromosomal abnormality in 21, a Mendelian disorder in 36 (autosomal recessive disorder: 23; autosomal dominant: 12; and X-linked recessive: 1), a MCA/MR syndrome in 9, and a CNS malformation in 6 patients. In 33 patients, a pre- or perinatal cause was found, and 20 patients presented a pre- or perinatal infection of the CNS. Finally, no etiological diagnosis was detected in 28 patients; 6 of them presented a hitherto unclassifiable type of familial mental retardation.

Atypical Prader-Willi syndrome with severe developmental delay and emaciation

A young boy showed features of Prader-Willi syndrome including hypotonia, cryptorchidism, a mildly dysmorphic facial appearance, a high-arched palate and an open triangular-shaped mouth, but had additional symptoms such as simian creases and multiple joint ankylosis in early infancy. Deletion of the long arm of chromosome 15(q11.2 to q13) was recognized. A muscle biopsy specimen showed variation in fiber size with hypertrophic type 1 fibers, type 2 fiber smallness, type 2B fiber paucity and an increased number of type 2C fibers. At the age of 4 1/2 years, he still showed severe developmental delay with severe muscle hypotonia, weakness and emaciation.

Deletions of proximal 15q without Prader-Willi syndrome

Fifteen patients with deletion of proximal 15q without typical Prader-Willi syndrome (PWS) have been reported previously [Schwartz et al, 1985]. We report on 2 additional patients without typical PWS found to have deletions of 15q11-13 on chromosome analysis done for evaluation of developmental delay. Their manifestations include broad nasal bridge with telecanthus, full nasal tip with flare of nasal alae, long upper lip, posteriorly angulated ears, highly arched palate, hypotonia, seizures and marked developmental delay. It was suggested that there may be a specific phenotype associated with this deletion which differs from PWS. Whether this deletion differs from the deletion associated with PWS awaits delineation on a molecular level.

Unique mosaicism in Prader-Labhart-Willi syndrome--a contiguous gene or aneuploidy syndrome?

A 16-year-old boy with Prader-Labhart-Willi syndrome (PLWS) had hypotonia, feeding difficulties, failure to thrive, strabismus and bilateral inguinal hernias with cryptorchidism during infancy followed by hyperphagia, marked early-onset obesity with insulin-dependent diabetes mellitus and necrobiosis lipoidica diabeticorum, short stature, hypogonadotropic hypogonadism and some of the facial characteristics of the individuals with the PLWS. IQ is estimated around 90. Cytogenetic studies showed mosaicism: 45,X, t(Y;15) with partial deletion 15 (15pter----15q12); 46,X, t(Y;15), dic (15)(15pter----15q12::15q12----15pter) and 47, X, t(Y;15), dic(15), dic(15). The dic(15) was bisatellited, NOR-positive on both arms and represented inv dup(15). Thus, the 2 lines with the dic(15) showed partial trisomy 15 (15pter----15q12) and partial pentasomy 15 (15pter----15q12), respectively. The cell line ratios were different in lymphocyte and fibroblast cultures. The unique cytogenetic findings in this patient, the reports of a variety of chromosome 15 aberrations in PLWS, as well as aberrations of other chromosomes, suggest that the condition is a contiguous gene syndrome rather than an aneuploidy syndrome.

Atypical phenotype associated with deletion (15) (pter----q11::q13----qter)

We report on a 10-year-old boy with an interstitial deletion within the region of bands 15q11----q13. Authors have associated the manifestation of the Prader-Willi syndrome (PWS) with variable deletions involving the bands q11----q13. Our patient had atypical manifestations not usually associated with PWS, ie, normal stature, proportionally sized hands and feet, normal genitalia, and was nonambulatory and severely mentally retarded. This case emphasized the clinical diversity seen in proximal 15q deletions in the region considered to be correlated with the PWS.

Non-reciprocal translocation (5;15), isodicentric (15) and Prader-Willi syndrome

A non-reciprocal translocation (5;15) and an isodicentric (15) resulting in trisomy 15pter----15q1?3 and monosomy 5qter [46,XY,-5,-15,+der(5)t(5;15) (5pter----5q35::15q13----15qter),+idic(15) (pter----q1?3::q1?3----pter)] was found in a 28-year-old profoundly retarded male resident of a state institution. Early developmental history and childhood and adult physical findings resembled those of Prader-Willi syndrome (PWS) patients. The parents' unbanded chromosomes were normal. Blood groups of parents and propositus were uninformative with regard to identifying gene deletions or duplications.

Chromosome abnormalities in pupils attending ESN/M schools

One hundred and sixty six children attending educationally subnormal/mild (ESN/M) schools were karyotyped as part of a project investigating the aetiology of mild mental retardation. Nine had significant chromosome abnormalities. Five of six children identified during the survey had no dysmorphic features--47,XXY (two), 48,XXYY, 46,XX 15q-, and 46,XX,t(X;19). One dysmorphic boy had a balanced translocation--46,XY,t(3;15). Three were already known--47,XX+21 (two) and 46,XY, 14q+. We suggest that routine karyotyping of children with mild mental retardation be considered.