Subtelomeric monosomy 11q and trisomy 16q in siblings and an unrelated child: molecular characterization of two der(11)t(11;16)

We report here three children with a der(11)t(11;16), two sibs (patients 1 and 2) having inherited a recombinant chromosome from a maternal t(11;16)(q24.3;q23.2) and a third unrelated child with a de novo der(11)t(11;16)(q25;q22.1), leading to partial monosomy 11q and trisomy 16q. Fluorescent in situ hybridization (FISH) using bacterial artificial chromosome (BAC) clones and array‐CGH were performed to determine the breakpoints involved in the familial and the de novo rearrangements. The partial 11 monosomy extended from 11q24.3 to 11qter and measured 6.17–6.21 Mb in Patients 1 and 2 while the size of the partial 11q25‐>qter monosomy was estimated at 1.97–2.11 Mb for Patient 3. The partial 16 trisomy extended from 16q23.2 to 16qter and measured 8.93–8.95 Mb in Patients 1 and 2 while the size of the partial 16q22.1‐>qter trisomy was 20.82 Mb for Patient 3. Intraventricular hemorrhage and transitional thrombocytopenia were found in both sibs but not in the third patient. The FLI1 gene, which is the most relevant gene for thrombocytopenia in Jacobsen syndrome, was neither deleted in family A nor in Patient 3. We suggest that a positional effect could affect the FLI1 expression for these two sibs. Deafness of our three patients confirmed the association of this anomaly to 11q monosomy and tended to confirm the hypothetic role of DFNB20 in Jacobsen syndrome hearing loss. Both sibs shared most of the features commonly observed in Jacobsen syndrome, but not the third patient. This confirmed that terminal 11q trisomy spanning 1 to 1.97–2.11 Mb is not associated with a typical Jacobsen syndrome. © 2011 Wiley‐Liss, Inc.     

Clinical and molecular cytogenetic studies in ring chromosome 5: report of a child with congenital abnormalities

We report here a child with a ring chromosome 5 (r(5)) associated with facial dysmorphology and multiple congenital abnormalities. Fluorescent in situ hybridization (FISH) using bacterial artificial chromosome (BAC) clones was performed to determine the breakpoints involved in the r(5). The 5p deletion extended from 5p13.2-3 to 5pter and measured 34.61 Mb (range: 33.7-35.52 Mb) while the 5q deletion extended from 5q35.3 to 5qter and measured 2.44 Mb (range: 2.31-2.57 Mb). The patient presented signs such as microcephaly, hypertelorism, micrognathia and epicanthal folds, partially recalling those of a deletion of the short arm of chromosome 5 and the "cri-du-chat" syndrome. The most striking phenotypic features were the congenital heart abnormalities which have been frequently reported in deletions of the distal part of the long arm of chromosome 5 and in rings leading to a 5q35-5qter deletion. However, the NKX2-5 gene, which has been related to congenital heart defects, was not deleted in our patient, nor presumably to some other patients with 5q35.3-5qter deletion. We propose that VEGFR3, deleted in our patient, could be a candidate gene for the congenital heart abnormalities observed.     

Molecular characterization of a patient with central nervous system dysmyelination and cryptic unbalanced translocation between chromosomes 4q and 18q

We report on a 12-year-old boy who presented with delayed development and CNS dysmyelination. Genetic studies showed a normal 46,XY karyotype by routine cytogenetic analysis, and 46,XY.ish del(18)(q23)(D18Z1+, MBP-) by FISH using a locus-specific probe for the MBP gene (18q23). Though the patient appeared to have normal chromosome 18s by repeated high resolution banding analysis, his clinical features were suggestive of a deletion of 18q. These included hearing loss secondary to stenosis of the external auditory canals, abnormal facial features, and foot deformities. FISH studies with genomic probes from 18q22.3 to 18qter confirmed a cryptic deletion which encompassed the MBP gene. In an attempt to further characterize the deletion, whole genome screening was conducted using array based comparative genomic hybridization (array CGH) analysis. The array CGH data not only confirmed a cryptic deletion in the 18q22.3 to 18qter region of approximately 7 Mb, it also showed a previously undetected 3.7 Mb gain of 4q material. FISH studies demonstrated that the gained 4q material was translocated distal to the 18qter deletion breakpoint. The 18q deletion contains, in addition to MBP, other known genes including CYB5, ZNF236, GALR1, and NFATC1, while the gained 4q material includes the genes FACL1 and 2, KLKB1, F11 and MTNR1A. The use of these combined methodologies has resulted in the first reported case in which array CGH has been used to characterize a congenital chromosomal abnormality, highlighting the need for innovative molecular cytogenetic techniques in the diagnosis of patients with idiopathic neurological abnormalities.     

11q24-q25缺失2例临床表型及文献复习

目的应用全基因组微阵列芯片平台,对临床发现的多发性畸形患儿进行全基因组拷贝数变异（CNVs）的检测,并寻找基因型与临床表型的关系。方法采用cytogenetic whole genome芯片筛查全基因组CNVs,针对发现的CNVs进行分析,参照国际基因组CNVs多态性数据库除外正常人群多态性CNVs。结合本研究2例与已报道的Jacobsen综合征（JBS）患儿的临床表型进行比较。结果 2例患儿SNP芯片分析为11q24-q25缺失（7.5和5.6Mb）,均为末端的非单纯性缺失,例1存在12号染色体短臂的较大片段重复（11.5Mb）,例2存在11号染色体短臂的大片段重复（32.5Mb）。2例共同缺失的部分均为JBS的关键区段,但临床表型与已报道的JBS患儿有所区别。2例均表现为头面部畸形、心血管系统异常和头颅影像学异常,均未发现血液系统异常。例1还表现为隐睾,例2表现为脾肿大。结论对临床上难以诊断的多发性畸形可采用全基因组CNVs检测,以帮助明确诊断,对于丰富这一区段临床表型信息具有重要意义,尤其针对罕见疾病,更多的相似报道的后续出现,才能使建立表型-基因型关联性成为可能。     

Pure subtelomeric microduplications as a cause of mental retardation

Submicroscopic subtelomeric aberrations are a common cause of mental retardation (MR). New molecular techniques allow the identification of subtelomeric microduplications, but their frequency and significance are largely unknown. We determined the frequency of subtelomeric, pure microduplications in a cohort of 624 patients with MR and/or multiple congenital anomalies using multiplex ligation dependent probe amplification (MLPA) and delineated the identified microduplications using array based comparative genomic hybridization (array CGH). In 11 patients, MLPA revealed a subtelomeric duplication without a concurrent deletion. Additional fluorescence in situ hybridization studies and parental analyses showed that three had occurred de novo: one duplication 5q34qter (12.7 Mb), one duplication 9q34.13qter (7.2 Mb) and one duplication 9p24.2pter (4.1 Mb). Five microduplications (9p, 11q, 12q, 15q and 16p) appeared to be inherited from an unaffected parent, while in three cases (9p, 12p and 17p) the parents were not available for testing. Based on our findings and data from the literature, the three de novo duplications were the only ones likely to be disease-causing, leading to a frequency of pathogenic subtelomeric, pure microduplications of 0.5%. Our study shows that subtelomeric microduplications are an infrequent cause of MR and that additional clinical and family studies are required to assess their clinical significance.     

Familial 4.8 MB deletion on 18q23 associated with growth hormone insufficiency and phenotypic variability

The deletion of the long arm of chromosome 18 causes a contiguous gene deletion syndrome with a highly variable phenotype, usually related to the extent of the deleted region. The most commonly reported clinical features include: decreased growth, microcephaly, facial abnormalities, hypotonia, developmental delay, intellectual disability, congenital aural atresia with hearing impairment and limb anomalies. Here we report on a familial terminal deletion of 18q23 region transmitted from a mother to two daughters, resulting in a remarkable phenotypic variability. The deletion was first detected by conventional cytogenetic analysis in one daughter and subsequently characterized using fluorescence in situ hybridization (FISH) and array-CGH. FISH analysis using subtelomeric 18p and 18q probes confirmed the 18qter deletion in the three patients, and FISH with a whole chromosome painting probe specific for chromosome 18 excluded rearrangements with other chromosomes. Array-CGH analysis allowed us to precisely define the extent of the deletion, which spans 4.8?Mb from 71,236,891 to 76,093,303 genomic positions and includes GALR1 and MBP genes, among others. High-resolution analysis of the deletion, besides a detailed clinical assessment, has provided important data for phenotype-genotype correlation and genetic counseling in this family. Furthermore, this study adds valuable information for phenotype-genotype correlation in 18q- syndrome and might facilitate future search for candidate genes involved in each phenotypic trait.     

Association of Jacobsen syndrome and bipolar affective disorder in a patient with a de novo 11q terminal deletion

We report on a young woman with Jacobsen syndrome (JBS) who was admitted to our psychiatric department because of a bipolar affective disorder (BPAD). Chromosome analysis was performed due to the fact that she had mental retardation, short stature, and subtle facial anomalies. A deletion of the distal long arm of chromosome 11 was found. A detailed mapping of the deletion breakpoint by quantitative real time PCR revealed a true terminal 11q deletion of approximately 8 Mb corresponding to the karyotype 46,XX,del(11)(q24.2). Polymorphic DNA marker analysis showed that the deletion is located on the paternal chromosome. Additionally, laboratory investigations revealed a low platelet count and magnetic resonance imaging of the brain showed white matter T2 hyperintensities in frontotemporal regions, which are unlikely to result from a demyelinating process as indicated by localized proton magnetic resonance spectroscopy. To our knowledge, this is the first report describing a BPAD in a case with JBS.     

Detection and delineation of an unusual 17p11.2 deletion by array-CGH and refinement of the Smith-Magenis syndrome minimum deletion to approximately 650 kb

Smith-Magenis syndrome (SMS) is a multiple congenital anomaly/mental retardation syndrome and it is characterized by an interstitial deletion of chromosome 17p11.2. SMS patients have a distinct phenotype which is believed to be caused by haploinsufficiency of one or more genes in the associated deleted region. Five non-deletion patients with classical phenotypic features of SMS have been reported with mutations in the retinoic acid induced 1 (RAI1) gene, located within the SMS critical interval. Happloinsufficiency of the RAI1 gene is likely to be the responsible gene for the majority of the SMS features, but other deleted genes in the SMS region may modify the overall phenotype in the patients with 17p11.2 deletions. SMS is usually diagnosed in the clinical genetic setting by FISH analysis using commercially available probes. We detected a submicroscopic deletion in 17p11.2 using array-CGH with a resolution of approximately 1 Mb in a patient with the SMS phenotype, who was not deleted for the commercially available SMS microdeletion FISH probe. Delineation of the deletion was performed using a 32K tiling BAC-array, containing 32,500 BAC clones. The deletion in this patient was size mapped to 2.7 Mb and covered the RAI1 gene. This case enabled the refinement of the SMS minimum deletion to approximately 650 kb containing eight putative genes and one predicted gene. In addition, it demonstrates the importance to investigate deletion of RAI1 in SMS patients.     

No evidence for submicroscopic 22qter deletions in patients with features suggestive for Angelman syndrome

Patients with monosomy 22q13.3 --> qter have, in addition to (usually severe) developmental delay, hypotonia, severe expressive language delay leading to absence of speech, pervasive developmental abnormalities, and subtle facial anomalies. Thus far, it has been one of the more common submicroscopic telomere deletions seen in patients with mental retardation. Due to the phenotypic overlap between monosomy 22q13.3 and Angelman syndrome (AS), 44 patients with AS features but without one of the characteristic molecular 15q abnormalities were tested for 22qter deletions. In the study group, 31/44 (70%) were heterozygous for locus D22S163 with probe cMS607 (distance 0.125 Mb from telomere). The remaining 13/44 (30%) patients were heterozygous for one or more of four microsatellite markers centromeric from D22S163 in the 22qter region (distances 1.5-4.3 Mb from telomere). Based on the present study, there is no evidence that patients with an "Angelman-like" phenotype are more likely to have a 22qter deletion than other individuals with mental retardation.     

Molecular characterization of an 11q interstitial deletion in a patient with the clinical features of Jacobsen syndrome

The 11q terminal deletion disorder or Jacobsen syndrome is a contiguous gene disorder. It is characterized by psychomotor retardation, cardiac defects, blood dyscrasias (Paris-Trousseau syndrome) and craniofacial anomalies. We report on a female patient with an approximately 10 Mb interstitial deletion with many of the features of Jacobsen syndrome: A congenital heart defect, dysmorphic features, developmental delay, and Paris-Trousseau syndrome. The karyotype of the patient is 46,XX,del(11)(q24.1q24.3). The interstitial deletion was confirmed using FISH probes for distal 11q, and the breakpoints were characterized by microarray analysis. This is the first molecularly characterized interstitial deletion in a patient with the clinical features of Jacobsen syndrome. The deletion includes FLI-1, but not JAM-3, which will help to determine the critical genes involved in this syndrome.     

Cryptic t(1;12)(q44;p13.3) translocation in a previously described syndrome with polymicrogyria,segregating as an apparently X-linked trait

We report on the multistep progression to the correct genetic diagnosis in an apparently new syndrome of mental retardation and multiple congenital anomalies, including hypogenitalism and polymicrogyria. We had previously reported it as an X-linked condition affecting four members (three males and one female) of a family [Zollino et al., 1992: Am J Med Genet 43:452-457]. Two of the four patients, both males, presented with a brain abnormality that was initially described as pachygyria, while the remaining two (one male and one female) did not. Our present study includes a clinical follow-up on the patients, neuroradiological reexamination of one patient, X linkage studies and X inactivation analyses, and finally molecular cytogenetics, which allowed us to establish definitely the genetic causes of the condition. After the detection of a subtle t(1;12)(q44;p13.3) balanced translocation in healthy carriers, two unbalanced segregation products were observed in different patients, resulting in 1q44qter monosomy and 12p13.3pter trisomy in patients with polymicrogyria and severe psychomotor delay, 12p13.3pter monosomy and 1q44qter trisomy in the other two patients without polymicrogyria, with less severe mental retardation and less distinctive physical anomalies. Thus, this condition is no longer to be considered X-linked, but the result of cryptic autosomal imbalance. Furthermore, this study identified an approximately 14 Mb interval in 1q44qter pathogenetically related to polymicrogyria.     

A 6.9 Mb 1qter deletion/4.4 Mb 18pter duplication in a boy with extreme microcephaly with simplified gyral pattern, vermis hypoplasia and corpus callosum agenesis

We here report a boy presenting with developmental delay, growth retardation, facial dysmorphisms, vermis hypoplasia, micropolygyria and corpus callosum agenesis. Conventional and high resolution cytogenetic analyses were normal but high resolution oligonucleotide array-CGH, performed at the age of 4 years, allowed the characterisation of a de novo 6.9 Mb 1qter deletion/4.4 Mb 18pter duplication. Numerous 1qter deletions have already been described associated with brain malformations. Among 1q44 deleted genes, AKT3 is the strongest candidate gene for vermis hypoplasia and corpus callosum agenesis.     

11q24.2q24.3 microdeletion in two families presenting features of Jacobsen syndrome,without intellectual disability: Role of FLI1, ETS1, and SENCR long noncoding RNA

This report presents two families with interstitial 11q24.2q24.3 deletion, associated with malformations, hematologic features, and typical facial dysmorphism, observed in Jacobsen syndrome (JS), except for intellectual disability (ID). The smallest 700 Kb deletion contains only two genes: FLI1 and ETS1, and a long noncoding RNA, SENCR, narrowing the minimal critical region for some features of JS. Consistent with recent literature, it adds supplemental data to confirm the crucial role of FLI1 and ETS1 in JS, namely FLI1 in thrombocytopenia and ETS1 in cardiopathy and immune deficiency. It also supports that combined ETS1 and FLI1 haploinsufficiency explains dysmorphic features, notably ears, and nose anomalies. Moreover, it raises the possibility that SENCR, a long noncoding RNA, could be responsible for limb defects, because of its early role in endothelial cell commitment and function. Considering ID and autism spectrum disorder, which are some of the main features of JS, a participation of ETS1, FLI1, or SENCR cannot be excluded. But, considering the normal neurodevelopment of our patients, their role would be either minor or with an important variability in penetrance. Furthermore, according to literature, ARHGAP32 and KIRREL3 seem to be the strongest candidate genes in the 11q24 region for other Jacobsen patients.     

A common molecular basis for rearrangement disorders on chromosome 22q11.

The chromosome 22q11 region is susceptible to rearrangements that are associated with congenital anomaly disorders and malignant tumors. Three congenital anomaly disorders, cat-eye syndrome, der() syndrome and velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS) are associated with tetrasomy, trisomy or monosomy, respectively, for part of chromosome 22q11. VCFS/DGS is the most common syndrome associated with 22q11 rearrangements. In order to determine whether there are particular regions on 22q11 that are prone to rearrangements, the deletion end-points in a large number of VCFS/DGS patients were defined by haplotype analysis. Most VCFS/DGS patients have a similar 3 Mb deletion, some have a nested distal deletion breakpoint resulting in a 1.5 Mb deletion and a few rare patients have unique deletions or translocations. The high prevalence of the disorder in the population and the fact that most cases occur sporadically suggest that sequences at or near the breakpoints confer susceptibility to chromosome rearrangements. To investigate this hypothesis, we developed hamster-human somatic hybrid cell lines from VCFS/DGS patients with all three classes of deletions and we now show that the breakpoints occur within similar low copy repeats, termed LCR22s. To support this idea further, we identified a family that carries an interstitial duplication of the same 3 Mb region that is deleted in VCFS/DGS patients. We present models to explain how the LCR22s can mediate different homologous recombination events, thereby generating a number of rearrangements that are associated with congenital anomaly disorders. We identified five additional copies of the LCR22 on 22q11 that may mediate other rearrangements leading to disease.     

Detection and delineation of an unusual 17p11.2 deletion by array-CGH and refinement of the Smith–Magenis syndrome minimum deletion to 650 kb

Smith–Magenis syndrome (SMS) is a multiple congenital anomaly/mental retardation syndrome and it is characterized by an interstitial deletion of chromosome 17p11.2. SMS patients have a distinct phenotype which is believed to be caused by haploinsufficiency of one or more genes in the associated deleted region. Five non-deletion patients with classical phenotypic features of SMS have been reported with mutations in the retinoic acid induced 1 (RAI1) gene, located within the SMS critical interval. Happloinsufficiency of the RAI1 gene is likely to be the responsible gene for the majority of the SMS features, but other deleted genes in the SMS region may modify the overall phenotype in the patients with 17p11.2 deletions. SMS is usually diagnosed in the clinical genetic setting by FISH analysis using commercially available probes. We detected a submicroscopic deletion in 17p11.2 using array-CGH with a resolution of approximately 1 Mb in a patient with the SMS phenotype, who was not deleted for the commercially available SMS microdeletion FISH probe. Delineation of the deletion was performed using a 32K tiling BAC-array, containing 32,500 BAC clones. The deletion in this patient was size mapped to 2.7 Mb and covered the RAI1 gene. This case enabled the refinement of the SMS minimum deletion to 650 kb containing eight putative genes and one predicted gene. In addition, it demonstrates the importance to investigate deletion of RAI1 in SMS patients.     

Chromosome 2p15p16.1 microdeletion syndrome: 2.5 Mb deletion in a patient with renal anomalies, intractable seizures and a choledochal cyst

Chromosome 2p15p16.1 microdeletion is an emerging syndrome recently described in patients with dysmorphic facial features, congenital microcephaly, mild to moderate developmental delay and neurodevelopmental abnormalities. Using clinical ultra-high resolution Affymetrix SNP 6.0 array we identified a de novo interstitial deletion on the short arm of chromosome 2, spanning approximately 2.5 Mb in the cytogenetic band position 2p15p16.1, in a female infant with characteristic features of 2p15p16.1 deletion syndrome including severe developmental delay, congenital microcephaly, intractable epilepsy, and renal anomalies, as well as a congenital choledochal cyst which has not been previously reported in other patients with this cytogenetic defect. We further redefined the previously reported critical region, supporting the presence of a newly recognized microdeletion syndrome involving haploinsufficiency of one or more genes deleted within at least a 1.1 Mb segment of the 2p15p16.1 region.     

DNA analysis of AHI1, NPHP1 and CYCLIN D1 in Joubert syndrome patients from the Netherlands

Joubert syndrome (JBS) is a clinically variable and genetically heterogeneous developmental brain disorder with autosomal recessive inheritance. Five genes, AHI1, NPHP1, CEP290, MKS3, and RPGRIP1L, and two additional loci on chromosome 9 and 11 have been identified so far. The relative contributions of AHI1 mutations and NPHP1 deletions have not yet been determined in a population-based JBS patient cohort. We therefore undertook a nationwide survey of JBS in the Netherlands and performed DNA analysis of the AHI1 and NPHP1 genes, as well as a new candidate gene CYCLIN D1. We obtained clinical data and DNA samples of 25 Dutch JBS patients. DNA analysis of AHI1 revealed pathogenic homozygous or compound heterozygous AHI1 mutations in four patients (16%). Based on the birth prevalence of about 1 in 100,000 for JBS in the Netherlands, we estimated a carrier frequency of AHI1 mutations of approximately 1 in 400. In another two patients, the AHI1 mutation Arg830Trp was identified (homozygously and heterozygously), a possible low penetrance allele. No deletions of NPHP1 or CYCLIN D1 mutations were detected in these 25 patients. In the four patients with AHI1 mutations, retinal disease (Leber congenital amaurosis or retinal dystrophy) was present in two, whereas none had renal disease. Pooling our data and data from the literature, retinal disease seems to occur in 75% of AHI1-associated JBS patients. Renal disease is present in 10% at most. We conclude that AHI1 mutations are an important cause of JBS in Dutch patients, and should always be looked for in patients suspected of JBS, especially when retinal dystrophy is present. Patients with AHI1 mutations should be regularly checked for retinal and renal disease up until adolescence.     

Array-CGH analysis and clinical description of 2q37.3 de novo subtelomeric deletion

We report on a 13-year-old girl with normal karyotype and a de novo cryptic terminal deletion of chromosome 2q, detected by subtelomeric FISH analysis. Further investigation with array-CGH analysis using the 1Mb resolution Spectral Chip 2600 (Spectral Genomics) confirmed the deletion and also showed a deletion of four additional clones. No other abnormalities were detected by array-CGH. FISH studies using 8 BAC-probes were performed for fine mapping of the deletion and confirmed the array results. FISH analysis showed that the deletion breakpoint lies between clones RP11-84G18 and RP11-83N2 (physical distance between clones 0.36Mb) and extends to the telomere. The size of the deletion was estimated to be about 6.4-6.7Mb. Clinical findings include: developmental delay, severe behavioural disturbances, growth-pubertal retardation, congenital conductive mild hearing loss, growth hormone deficiency, compensate hypothyroidism, dysmorphic facial features, excessive joint hypermobility, brachymetaphalangy, abnormal dermatoglyphics and a history of neonatal laryngomalacia, hypotonia and umbilical hernia. The phenotype of our patient is in keeping with those of the literature, with the exception of cardiovascular, urogenital, neurological anomalies and eczema, which were not observed. The report of the clinical and molecular presentation of similar cases will allow accurate phenotype-genotype correlation and proper genetic counseling of the family.     

Detection of an unexpected subtelomeric 15q26.2 --> qter deletion in a little girl: clinical and cytogenetic studies

Unlike the small proximal 15q deletions causing Prader-Willi and/or Angelman syndrome, distal deletions of the terminal long arm of chromosome 15 have rarely been described. To the best of our knowledge, only four patients with a pure terminal 15q deletion have been documented in the literature. We report here on an unexpected abnormal hybridization pattern for the 15q specific subtelomeric control probe (clone 154P1) of the commercial SNRPN probe in a girl referred for suspicion of Angelman syndrome. Investigation by fluorescent in situ hybridization (FISH) using bacterial artificial chromosome (BAC) clones defined a partial monosomy 15q26.2 --> 15qter for a minimal critical region of approximately 5.7 Mb, which is the most distal de novo 15qter deletion reported to date. All the de novo 15qter deletion cases, including ours, presented with pre- and post-natal growth retardation related to the loss of one copy of the IGF1R gene. Based on the comparaison with the previous published cases and owing to the clinical phenotype of our patient, we define a new subtelomeric 15qter syndrome which would be characterized by intrauterine growth retardation and global post-natal growth failure, variable mental retardation, facial anomalies including relative micrognathia and triangular facies and minor malformations of the extremities including proximally placed thumbs, cubitus valgus, and brachydactyly with tappering of the digits.     

A double cryptic chromosome imbalance is an important factor to explain phenotypic variability in Wolf-Hirschhorn syndrome

A total of five Wolf-Hirschhorn syndrome (WHS) patient with a 4p16.3 de novo microdeletion was referred because of genotype-phenotype inconsistencies, first explained as phenotypic variability of the WHS. The actual deletion size was found to be about 12 Mb in three patients, 5 Mb in another one and 20 Mb in the last one, leading us to hypothesize the presence of an extrachromosome segment on the deleted 4p. A der(4)(4qter --> p16.1::8p23 --> pter) chromosome, resulting from an unbalanced de novo translocation was, in fact, detected in four patients and a der(4)(4qter --> q32::4p15.3 --> qter) in the last. Unbalanced t(4;8) translocations were maternal in origin, the rec(4p;4q) was paternal. With the purpose of verifying frequency and specificity of this phenomenon, we investigated yet another group of 20 WHS patients with de novo large deletions (n = 13) or microdeletions (n = 7) and with apparently straightforward genotype-phenotype correlations. The rearrangement was paternal in origin, and occurred as a single anomaly in 19 out of 20 patients. In the remaining patient, the deleted chromosome 4 was maternally derived and consisted of a der(4)(4qter --> 4p16.3::8p23 --> 8pter). In conclusions, we observed that 20% (5/25) of de novo WHS-associated rearrangements were maternal in origin and 80% (20/25) were paternal. All the maternally derived rearrangements were de novo unbalanced t(4;8) translocations and showed specific clinical phenotypes. Paternally derived rearrangements were usually isolated deletions. It can be inferred that a double, cryptic chromosome imbalance is an important factor for phenotypic variability in WHS. It acts either by masking the actual deletion size or by doubling a quantitative change of the genome.