Drayer's syndrome of mental retardation, microcephaly, short stature and absent phalanges is caused by a recurrent deletion of chromosome 15(q26.2-->qter)

Evidence for NR2F2/COUP-TFII involvement in human testis development

NR2F2 encodes COUP-TFII, an orphan nuclear receptor required for the development of the steroidogenic lineages of the murine fetal testes and ovaries. Pathogenic variants in human NR2F2 are associated with testis formation in 46,XX individuals, however, the function of COUP-TFII in the human testis is unknown. We report a de novo heterozygous variant in NR2F2 (c.737G > A, p.Arg246His) in a 46,XY under-masculinized boy with primary hypogonadism. The variant, located within the ligand-binding domain, is predicted to be highly damaging. In vitro studies indicated that the mutation does not impact the stability or subcellular localization of the protein. NR5A1, a related nuclear receptor that is a key factor in gonad formation and function, is known to physically interact with COUP-TFII to regulate gene expression. The mutant protein did not affect the physical interaction with NR5A1. However, in-vitro assays demonstrated that the mutant protein significantly loses the inhibitory effect on NR5A1-mediated activation of both the LHB and INSL3 promoters. The data support a role for COUP-TFII in human testis formation. Although mutually antagonistic sets of genes are known to regulate testis and ovarian pathways, we extend the list of genes, that together with NR5A1 and WT1, are associated with both 46,XX and 46,XY DSD.

Heterozygous rare variants in NR2F2 cause a recognizable multiple congenital anomaly syndrome with developmental delays

Nuclear receptor subfamily 2 group F member 2 (NR2F2 or COUP-TF2) encodes a transcription factor which is expressed at high levels during mammalian development. Rare heterozygous Mendelian variants in NR2F2 were initially identified in individuals with congenital heart disease (CHD), then subsequently in cohorts of congenital diaphragmatic hernia (CDH) and 46,XX ovotesticular disorders/differences of sexual development (DSD); however, the phenotypic spectrum associated with pathogenic variants in NR2F2 remains poorly characterized. Currently, less than 40 individuals with heterozygous pathogenic variants in NR2F2 have been reported. Here, we review the clinical and molecular details of 17 previously unreported individuals with rare heterozygous NR2F2 variants, the majority of which were de novo. Clinical features were variable, including intrauterine growth restriction (IUGR), CHD, CDH, genital anomalies, DSD, developmental delays, hypotonia, feeding difficulties, failure to thrive, congenital and acquired microcephaly, dysmorphic facial features, renal failure, hearing loss, strabismus, asplenia, and vascular malformations, thus expanding the phenotypic spectrum associated with NR2F2 variants. The variants seen were predicted loss of function, including a nonsense variant inherited from a mildly affected mosaic mother, missense and a large deletion including the NR2F2 gene. Our study presents evidence for rare, heterozygous NR2F2 variants causing a highly variable syndrome of congenital anomalies, commonly associated with heart defects, developmental delays/intellectual disability, dysmorphic features, feeding difficulties, hypotonia, and genital anomalies. Based on the new and previous cases, we provide clinical recommendations for evaluating individuals diagnosed with an NR2F2-associated disorder.

15q26 deletion in a patient with congenital heart defect, growth restriction and intellectual disability: case report and literature review

Background

15q26 deletion is a relatively rare chromosomal disorder, and it is described only in few cases. Patients with this aberration show many signs and symptoms, particularly pre- and postnatal growth restriction, developmental delay, microcephaly, intellectual disability and various congenital malformations.

Case presentation

We report on a girl, 4 years old, of consanguineous parents, with a 15q26 deletion. Clinical manifestations included failure to thrive, developmental delay, microcephaly, dysmorphic facies with broad forehead, hypertelorism, narrowed eyelid slits and protruding columella. The patient also showed skeletal abnormalities, especially clinodactyly of the 5th finger, varus equine right foot and left club foot. Additionally, she had teething delay and divergent strabismus. Heart ultrasound displayed two atrial septal defects with left-to-right shunt, enlarging the right cavities. Routine cytogenetic analysis revealed a shortened 15q chromosome. Subsequent array analysis disclosed a terminal 9.15 Mb deletion at subband 15q26.1-q26.3. Four candidate genes associated with 15q26 deletion phenotype were within the deleted region, i.e. IGF1R, NR2F2, CHD2 and MEF2A.

Conclusion

We report on an additional case of 15q26 monosomy, characterized by array-CGH. Molecular cytogenetic analysis allowed us to identify the exact size of the deletion, and four candidate genes for genotype-phenotype correlation. 15q26 monosomy should be considered when growth retardation is associated with hearing anomalies and congenital heart defect, especially atrioventricular septal defects (AVSDs) and/or aortic arch anomaly (AAA).

Spread of X-chromosome inactivation into autosomal regions in patients with unbalanced X-autosome translocations and its phenotypic effects

Patients with unbalanced X-autosome translocations are rare and usually present a skewed X-chromosome inactivation (XCI) pattern, with the derivative chromosome being preferentially inactivated, and with a possible spread of XCI into the autosomal regions attached to it, which can inactivate autosomal genes and affect the patients' phenotype. We describe three patients carrying different unbalanced X-autosome translocations, confirmed by G-banding karyotype and array techniques. We analyzed their XCI pattern and inactivation spread into autosomal regions, through HUMARA, ZDHHC15 gene assay and the novel 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay, and identified an extremely skewed XCI pattern toward the derivative chromosomes for all the patients, and a variable pattern of late-replication on the autosomal regions of the derivative chromosomes. All patients showed phenotypical overlap with patients presenting deletions of the autosomal late-replicating regions, suggesting that the inactivation of autosomal segments may be responsible for their phenotype. Our data highlight the importance of the XCI spread into autosomal regions for establishing the clinical picture in patients carrying unbalanced X-autosome translocations, and the incorporation of EdU as a novel and precise tool to evaluate the inactivation status in such patients.

CHD2-Related CNS Pathologies

Epileptic encephalopathies (EE) are severe epilepsy syndromes characterized by multiple seizure types, developmental delay and even regression. This class of disorders are increasingly being identified as resulting from de novo genetic mutations including many identified mutations in the family of chromodomain helicase DNA binding (CHD) proteins. In particular, several de novo pathogenic mutations have been identified in the gene encoding chromodomain helicase DNA binding protein 2 (CHD2), a member of the sucrose nonfermenting (SNF-2) protein family of epigenetic regulators. These mutations in the CHD2 gene are causative of early onset epileptic encephalopathy, abnormal brain function, and intellectual disability. Our understanding of the mechanisms by which modification or loss of CHD2 cause this condition remains poorly understood. Here, we review what is known and still to be elucidated as regards the structure and function of CHD2 and how its dysregulation leads to a highly variable range of phenotypic presentations.

Case of 15q26-qter deletion associated with a Prader-Willi phenotype

Prader-Willi syndrome (PWS) is one of the common neurogenetic disorders associated with intellectual disability. PWS involves a complex inheritance pattern and is caused by an absence of gene expression on the paternally inherited 15q11.2-q13 region, either due to deletion, maternal uniparental disomy or imprinting defect. The syndrome is characterized principally by severe neonatal hypotonia, a weak suck in infancy that is later followed by hyperphagia and obesity, developmental delay, intellectual disability and short stature. In the case of the chromosome 15q26-qter deletion syndrome or Drayer's syndrome, very few reports have been published. Its characteristics include intrauterine growth restriction, postnatal growth failure, varying degrees of intellectual disability, developmental delay, typical facial appearance and diaphragmatic hernia. The present paper describes a female patient in whom clinical findings were suggestive of PWS and deletion in the 15q26-qter region. Both karyotyping and methylation-specific polymerase chain reaction were shown to be normal. Nevertheless, fluorescence in situ hybridization showed a 15qter deletion that was later mapped by single nucleotide polymorphism (SNP)-array. The deleted genomic region involves the insulin-like growth factor-1 receptor (IGF1R) gene, which is related to short stature, developmental delay and intellectual disability. This case had various clinical characteristics in common with the cases of 15q26-qter deletionand characteristics compatible with PWS.

Three Offspring with Cri-du-Chat Syndrome from Phenotypically Normal Parents

Cri-du-chat syndrome is characterized by facial dysmorphism, intellectual disability, and multiple congenital anomalies. Most cases occur de novo. Here, we report 3 siblings with cri-du-chat syndrome born to healthy parents. The proband was admitted to our clinic at the age of 6.5 years due to severe intellectual disability, facial dysmorphism, and heart defect. His karyotype showed a deletion of chromosome 5p. Microarray analysis revealed a 29-Mb deletion in chromosome 5p and a 4.7-Mb duplication in chromosome 19q. FISH analysis indicated an unbalanced translocation between 5p13.3 and 19q13.4. During follow-up, the second and the third child of the family were born with the same chromosome abnormality. Parental peripheral blood and skin fibroblast karyotypes as well as the FISH results using chromosome 5p- and 19q-specific subtelomeric probes were normal. FISH analysis of the father's sperm detected a 5p deletion in 12.8% of 200 cells, and microarray analysis confirmed the same unbalanced chromosome abnormality in a mosaic pattern. Uncultured peripheral blood and buccal smear of the father were also studied by FISH to exclude low-level mosaicism and in vitro culture effect. This is the first study that provides molecular evidence of paternal gonadal mosaicism of an unbalanced translocation detected in 3 siblings with cri-du-chat syndrome.

COUP-TF Genes, Human Diseases, and the Development of the Central Nervous System in Murine Models

COUP-TFI and -TFII are members of the steroid/thyroid nuclear receptor superfamily. Recent clinical studies reveal that COUP-TFI gene mutations are associated with Bosch-Boonstra-Schaaf optic atrophy syndrome displaying symptoms of optic atrophy, intellectual disability, hypotonia, seizure, autism spectrum disorders, oromotor dysfunction, thin corpus callosum, or hearing defects, and COUP-TFII gene mutations lead to congenital heart defects and/or congenital diaphragmatic hernia with developmental delay and mental defects. In this review, we first describe the functions of COUP-TF genes in the morphogenesis of mouse forebrain including cerebral cortex, hippocampus, amygdala complex, hypothalamus, and cortical interneuron. Then, we address their roles in the development of cerebellum, glial cells, neural crest cells, and adult neuronal stem cells. Clearly, the investigations on the functions of COUP-TF genes in the developing mouse central nervous system will benefit not only the understanding of neurodevelopment, but also the etiology of human mental diseases.

Somatic/gonadal mosaicism for structural autosomal rearrangements: female predominance among carriers of gonadal mosaicism for unbalanced rearrangements

Background

Mosaicism for chromosomal structural rearrangements (Rea) is rare and the timing and mechanisms of mosaic Rea formation, maintenance, and clinical manifestation are poorly understood. To date, there are no published data on the cytogenetic profile of mosaic Reas. The question as to whether the proportion of abnormal cells in the carrier’s cultured blood is clinically significant remains unanswered. A previous study showed a strong female preponderance among carriers of mosaicism for Rea with pericentromeric breaks, indicating female-specific instability in early embryos. However, there is no corresponding study on male to female sex ratio (SR) among carriers of somatic and/or gonadal mosaicism for non-centromeric Rea. Population rates of mosaic Rea carriers calculated from consecutive series of patients referred for various reasons and from prenatal samples have not been established. Therefore the objectives of the present study were several-fold: (1) a study on profiles of Rea involved, (2) comparative analysis of the proportion of cells with unbalanced Rea in blood cultures from asymptomatic and affected carriers, (3) comparative analysis of SR in carriers of mosaicism for balanced and unbalanced Rea, and (4) determination of the population frequency of mosaicism for autosomal Rea.

Results

One hundred and three cases of mosaicism for autosomal non-centromeric Rea (N/Rea; normal line/structural rearrangement) in which the sex of the carrier had been specified were identified in the literature. Among balanced Rea, there was a prevalence of reciprocal translocations (89 %) over inversions (11 %). Among unbalanced Rea, deletions were the most frequent (40 %), followed by duplications (25 %) and rings (16 %). Derivatives and other chromosome abnormalities were less frequent (9 and 10 %). Eight of eleven (73 %) affected carriers of unbalanced Rea displayed a high proportion (>50 %) of abnormal cells compared to 4/37 (11 %) in asymptomatic carriers, p < 0.0001. Among carriers of mosaicism for balanced Rea there was a slight male predominance, 24 M/22 F, unlike the strong female predominance among carriers of mosaicism for unbalanced Rea, 11 M/46 F, p < 0.0001. Among ten carriers of unbalanced Rea with reproductive failure, only one was a male with infertility, and one was a partner of a woman experiencing recurrent spontaneous abortion. Population rates of mosaics for reciprocal translocaton (N/rcp), inversion (N/inv), and unbalanced Rea (N/unbal Rea) calculated from published data on consecutive series of patients with reproductive failures were 0.02 ‰, 0.005 ‰, and 0.002 ‰, correspondingly. Among 30,376 infertile patients three carriers of mosaicism for balanced Rea were identified (two cases of N/rcp and one case of N/inv), whereas among 26,384 patients with habitual abortion seven carriers were detected (five N/rcp and two N/inv). Among all 56,760 tested patients with reproductive failures only one was found to be a carrier of mosaicism for an unbalanced Rea (N/del, mosaicism for deletion).

Conclusions

A high proportion of Rea cells (>50 %) detected in cultured T-lymphocytes is associated with clinical manifestation of chromosomal imbalance. A strong female prevalence among carriers of mosaicism for unbalanced Rea suggests male-specific selection against abnormal cells rather than impairment of male gametogenesis, as the latter suggests a better prognosis for male fetuses. These findings should be taken into consideration when genetic counseling of patients referred after a diagnosis of mosaicism for an unbalanced rearrangement in a fetus.

Chromosomal Imbalances in Patients with Congenital Cardiac Defects: A Meta-analysis Reveals Novel Potential Critical Regions Involved in Heart Development

OBJECTIVE

Congenital cardiac defects represent the most common group of birth defects, affecting an estimated six per 1000 births. Genetic characterization of patients and families with cardiac defects has identified a number of genes required for heart development. Yet, despite the rapid pace of these advances, mutations affecting known genes still account for only a small fraction of congenital heart defects suggesting that many more genes and developmental mechanisms remain to be identified.

DESIGN

In this study, we reviewed 1694 described cases of patients with cardiac defects who were determined to have a significant chromosomal imbalance (a deletion or duplication). The cases were collected from publicly available databases (DECIPHER, ISCA, and CHDWiki) and from recent publications. An additional 68 nonredundant cases were included from the University of Michigan. Cases with multiple chromosomal or whole chromosome defects (trisomy 13, 18, 21) were excluded, and cases with overlapping deletions and/or insertions were grouped to identify regions potentially involved in heart development.

RESULTS

Seventy-nine chromosomal regions were identified in which 5 or more patients had overlapping imbalances. Regions of overlap were used to determine minimal critical domains most likely to contain genes or regulatory elements involved in heart development. This approach was used to refine the critical regions responsible for cardiac defects associated with chromosomal imbalances involving 1q24.2, 2q31.1, 15q26.3, and 22q11.2.

CONCLUSIONS

The pattern of chromosomal imbalances in patients with congenital cardiac defects suggests that many loci may be involved in normal heart development, some with very strong and direct effects and others with less direct effects. Chromosomal duplication/deletion mapping will provide an important roadmap for genome-wide sequencing and genetic mapping strategies to identify novel genes critical for heart development.

Identification of dosage-sensitive genes in fetuses referred with severe isolated congenital diaphragmatic hernia

OBJECTIVE

Congenital diaphragmatic hernia (CDH) is a fetal abnormality affecting diaphragm and lung development with a high mortality rate despite advances in fetal and neonatal therapy. CDH may occur either as an isolated defect or in syndromic form for which the prognosis is worse. Although conventional karyotyping and, more recently, chromosomal microarrays support a substantial role for genetic factors, causal genes responsible for isolated CDH remain elusive. We propose that chromosomal microarray analysis will identify copy number variations (CNVs) associated with isolated CDH.

METHODS

We perform a prospective genome-wide screen for CNVs using chromosomal microarrays on 75 fetuses referred with apparently isolated CDH, six of which were later reclassified as non-isolated CDH.

RESULTS

The results pinpoint haploinsufficiency of NR2F2 as a cause of CDH and cardiovascular malformations. In addition, the 15q25.2 and 16p11.2 recurrent microdeletions are associated with isolated CDH. By using gene prioritisation and network analysis, we provide strong evidence for several novel dosage-sensitive candidate genes associated with CDH.

CONCLUSIONS

Chromosomal microarray analysis detects submicroscopic CNVs associated with isolated CDH or CDH with cardiovascular malformations.

Variable behavioural phenotypes of patients with monosomies of 15q26 and a review of 16 cases

Patients with trisomy or tetrasomy of distal 15q show a recognizable overgrowth syndrome, whereas patients with a monosomy of 15q26 share some degree of pre- and postnatal growth retardation, but differ with respect to facial and skeletal dysmorphisms, congenital heart disease and intellectual development. By reviewing 16 cases with losses of 15q26 we found that the size of the deletion was also not a predictor of the breadth of the phenotypic spectrum, the severity of disease or prognosis of the patient. Although monosomies of 15q26 do not represent a classical contiguous gene syndrome, a few candidate genes for selected features such as proportional growth retardation and cardiac abnormalities have been identified. In 11 out of 16 patients with monosomy of distal 15q variable neurobehavioral phenotypes, including learning difficulties, seizures, attention-deficit-hyperactivity disorder, hearing loss and autism, have been found. We discuss clinical ramifications for cases with a loss of 15q26 detected by prenatal array-CGH.

A rare non-Robertsonian translocation involving chromosomes 15 and 21

CONTEXT

Robertsonian translocations (RT) are among the most common balanced structural rearrangements in humans and comprise complete chromatin fusion of the long arm of two acrocentric chromosomes. Nevertheless, non-Robertsonian translocation involving these chromosomes is a rare event.

CASE REPORT

We report a de novo unbalanced translocation involving chromosomes 15 and 21. The newborn was the daughter of a 29-year-old mother and a 42-year-old father. The couple was non-consanguineous. Clinical findings led to the diagnosis of Down syndrome (DS) with severe congenital heart defects (persistent arterial duct, and complete atrioventricular septal defect), as well as low birth length and weight (< 5th and < 10th percentile, respectively, based on specific measurement curves for DS). Conventional cytogenetic analysis revealed the karyotype 46,XX,der(15)(15pter → 15q26.2::21q11.2 → 21 qter). The translocation was confirmed by means of fluorescence in situ hybridization. The parents had normal karyotypes.

CONCLUSIONS

Differently from RT, in our case a rare event occurred involving the distal segment of 15q and the proximal segment of 21q. Only two reports of this translocation, involving chromosomes 15 and 21 but different breakpoints, have been described so far. The association between 21q duplication and 15q deletion makes it difficult to separate the effect of each chromosome, but might also be responsible for increasing the growth retardation, as detected in our case. Cytogenetic analysis on DS patients is mandatory not only to confirm the diagnosis, but also to assess the risk of recurrence at genetic counseling, as well as to evaluate the contribution of other chromosome aberrations in the final phenotype.

Twenty-year cytogenetic and molecular follow-up of a patient with ring chromosome 15: a case report

Introduction

Ring chromosome 15 is a rare disorder, with only a few over 40 cases reported in the literature. There are only two previous reports of cases where patients with ring chromosome 15 have been followed-up.

Case presentation

We report here on the 20-year clinical and cytogenetic follow-up of a patient with a ring chromosome 15. Our patient, a Caucasoid Asian woman, presented with short stature, microcephaly, minor dysmorphic features, hyperextensible knees, generalized hirsutism, café-au-lait and small hypochromic spots spread over her face and the front of her chest and abdomen, dorsolumbar scoliosis and mild intellectual disability. She was followed-up from the age of eight to 28 years. When she was 27 years old, she was reported by her mother to present with compulsive overeating and an aggressive mood when challenged. Karyotyping revealed that the majority of her cells harbored one normal chromosome and one ring chromosome. Silver staining revealed the presence of the nucleolar organizer region in the ring chromosome. Ring loss and/or secondary aberrations exhibited a slight increase over time, from 4.67% in 1989 to 7.67% in 2009, with the presence of two monocentric rings, cells with interlocked rings, a dicentric ring, and broken or open rings. A genome-wide array technique detected a 5.5Mb deletion in 15q26.2.

Conclusions

We observed that some phenotypic alterations in our patient can be associated with gene loss and haploinsufficiency. Other features may be related to different factors, including ring instability and epigenetic factors.

Nail and phalangeal agenesis in a patient with 4pter and 9pter duplication

We report on an 8-month-old girl with intra-uterine growth retardation, microcephaly, incomplete cleft lip, axial hypotonia, failure to thrive, and brachydactyly type B (phalangeal agenesis and absence of nails). She carried a supernumerary marker chromosome derived from chromosomes 4 and 9, leading to 4pter-q12 and 9pter-p21.2 duplication. The marker was derived from the 3:1 segregation of a maternal balanced translocation 46,XX, t(4;9)(q12;p21.2). The proposita is the first reported individual with distal phalangeal agenesis and anonychia, and trisomy 4p and partial trisomy 9p due to 3:1 segregation of a maternal reciprocal translocation.

IGF1R mutations as cause of SGA

Until 2003 monogenetic aberrations that lead to a child that is born too small for gestational age (SGA) were poorly defined. With the first report of mutations within the insulin-like growth factor type 1 receptor (IGF1R) gene in two non-syndromic patients born SGA, who failed to thrive despite normal or even elevated IGF1 serum concentrations the concept of IGF1 resistance has been established. The identification of additional individuals bearing IGF1R mutations along with comparative, genetic, structural and biochemical studies has provided evidence for the pathogenic impact of the IGF1R mutations on human longitudinal growth. However, the variability in the occurrence of additional clinical manifestations, such as developmental delay, might indicate that the pleiotropic functions of the IGF-IGF1R system are partially redundant. It is apparent that we have just begun to unravel the multifaceted IGF1R actions at the interface of growth control, maintenance of metabolic homeostasis and neurodevelopment and neural protection.

Identification of chromosome 15q26 terminal deletion with telomere sequences and its bearing on genotype-phenotype analysis

We report a de novo heterozygous 5,013,940 bp terminal deletion of chromosome 15q26 in a 13 9/12 -year-old Japanese girl with short stature (-3.9 SD), mild mental retardation, and ventricular septal defect (VSD). This terminal deletion involved IGF1R but not NR2F2, and was associated with an addition of telomere repeat sequences (TTAGGG) at the end of the truncated chromosome. The results provide further support for the notion that terminal deletions are healed by de novo addition of telomere sequences essential for chromosome stability and DNA replication. Furthermore, while growth failure and mental retardation are primarily explained by loss of IGF1R, the occurrence of VSD might suggest the existence of a cardiac anomaly gene, other than the candidate cardiac anomaly gene NR2F2, in the deleted region.

Loss of CHSY1, a secreted FRINGE enzyme, causes syndromic brachydactyly in humans via increased NOTCH signaling

We delineated a syndromic recessive preaxial brachydactyly with partial duplication of proximal phalanges to 16.8 Mb over 4 chromosomes. High-throughput sequencing of all 177 candidate genes detected a truncating frameshift mutation in the gene CHSY1 encoding a chondroitin synthase with a Fringe domain. CHSY1 was secreted from patients' fibroblasts and was required for synthesis of chondroitin sulfate moieties. Noticeably, its absence triggered massive production of JAG1 and subsequent NOTCH activation, which could only be reversed with a wild-type but not a Fringe catalytically dead CHSY1 construct. In vitro, depletion of CHSY1 by RNAi knockdown resulted in enhanced osteogenesis in fetal osteoblasts and remarkable upregulation of JAG2 in glioblastoma cells. In vivo, chsy1 knockdown in zebrafish embryos partially phenocopied the human disorder; it increased NOTCH output and impaired skeletal, pectoral-fin, and retinal development. We conclude that CHSY1 is a secreted FRINGE enzyme required for adjustment of NOTCH signaling throughout human and fish embryogenesis and particularly during limb patterning.

Recurrent 70.8 Mb 4q22.2q32.3 duplication due to ovarian germinal mosaicism

A mosaicism is defined by the presence of two or more populations of cells with different genotypes in one individual. Chromosomal germinal mosaicism occurs in germ cells before the onset of meiosis. Previously, few studies have described germinal mosaicism. In this study, we report on two siblings who carried identical pure and direct interstitial 4q22.2q32.3 duplication. Procedure investigations included complete clinical description, conventional cytogenetic analysis, fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH) array experiments and microsatellite study searching for parental origin of the duplication. Microarray CGH and further FISH experiments with BAC clones showed the same 70.8 Mb direct duplication, dup(4)(q22.2q32.3). Molecular studies of the 4q duplication were consistent with maternal origin associated with mitotic or meiotic rearrangements. This structural chromosomal aberration was associated in both cases with increased nuchal translucency, growth retardation and dysmorphy. Cardiopathy and lung malformations were only evident in the first case. These clinical manifestations are similar to those previously reported in previous studies involving pure 4q trisomy of the same region, except for thumb and renal abnormalities that were not obvious in the presented cases. The amplified region included genes involved in neurological development (NEUROG2, MAB21L2, PCDH10/18 and GRIA2). The recurrent 4q duplication in these siblings is consistent with a maternal ovarian germinal mosaicism. This is the first description of germinal mosaicism for a large chromosomal duplication and highlights that genetic counselling for apparently de novo chromosome aberration should be undertaken with care.