Wolf-Hirschhorn syndrome-associated chromosome changes are not mediated by olfactory receptor gene clusters nor by inversion polymorphism on 4p16

Wolf-Hirschhorn syndrome: Prenatal diagnosis and molecular cytogenetic characterization of a de novo distal deletion of 4p (4p16.1 → pter) in a fetus with facial cleft and preaxial polydactyly

OBJECTIVE

We present prenatal diagnosis and molecular cytogenetic characterization of Wolf-Hirschhorn syndrome (WHS) in a fetus with facial cleft and preaxial polydactyly.

MATERIALS AND METHODS

A 37-year-old woman underwent amniocentesis at 18 weeks of gestation because of advanced maternal age, and the result showed an aberrant chromosome 4 or 46,XX,add(4) (p15.3). The woman consulted our clinics at 22 weeks of gestation and requested for repeat amniocentesis. Prenatal ultrasound revealed intrauterine growth restriction, facial cleft, vermian hypoplasia of cerebellum, micrognathia and absent stomach. Conventional cytogenetic analysis was performed on cultured amniocytes, parental bloods and cord blood. Array comparative genomic hybridization (aCGH) and quantitative fluorescent polymerase chain reaction (QF-PCR) were performed on the DNAs extracted from uncultured amniocytes and parental bloods. Fluorescence in situ hybridization (FISH) analysis was performed on cultured metaphase amniocytes.

RESULTS

aCGH analysis on uncultured amniocytes revealed arr 4p16.3p16.1 (74,447-8,732,731) × 1.0 [GRCh37 (hg19)] with an 8.66-Mb deletion of 4p16.3-p16.1 encompassing 70 [Online Mendelian Inheritance of in Man (OMIM)] genes including ZNF141, FGFRL1, TACC3, LETM1, NSD2 and NELFA. QF-PCR revealed a paternal origin of the distal 4p deletion. Conventional cytogenetic analysis revealed 46,XX,del(4) (p16.1)dn in the fetus. Metaphase FISH analysis confirmed a 4p16 deletion. The parental karyotypes were normal. The pregnancy was subsequently terminated, and a malformed fetus was delivered with typical WHS facial dysmorphism, bilateral cleft lip and palate, and preaxial polydactyly on the right hand.

CONCLUSION

aCGH, QF-PCR and FISH help to delineate the nature of a prenatally defected aberrant chromosome, and the acquired information is useful for genetic counseling.

Clinical and genetic characterization of ten Egyptian patients with Wolf-Hirschhorn syndrome and review of literature

Background

Wolf–Hirschhorn syndrome (WHS) (OMIM 194190) is a multiple congenital anomalies/intellectual disability syndrome. It is caused by partial loss of genetic material from the distal portion of the short arm of chromosome.

Methods

We studied the phenotype–genotype correlation.

Results

We present the clinical manifestations and cytogenetic results of 10 unrelated Egyptian patients with 4p deletions. Karyotyping, FISH and MLPA was performed for screening for microdeletion syndromes. Array CGH was done for two patients. All patients exhibited the cardinal clinical manifestation of WHS. FISH proved deletion of the specific WHS locus in all patients. MLPA detected microdeletion of the specific locus in two patients with normal karyotypes, while array CGH, performed for two patients, has delineated the extent of the deleted segments and the involved genes. LETM1, the main candidate gene for the seizure phenotype, was found deleted in the two patients tested by array CGH; nevertheless, one of them did not manifest seizures. The study emphasized the previous.

Conclusion

WHS is a contiguous gene syndrome resulting from hemizygosity of the terminal 2 Mb of 4p16.3 region. The Branchial fistula, detected in one of our patients is a new finding that, to our knowledge, was not reported.

Subtelomeric Copy Number Variations: The Importance of 4p/4q Deletions in Patients with Congenital Anomalies and Developmental Disability

The most prevalent structural variations in the human genome are copy number variations (CNVs), which appear predominantly in the subtelomeric regions. Variable sizes of 4p/4q CNVs have been associated with several different psychiatric findings and developmental disability (DD). We analyzed 105 patients with congenital anomalies (CA) and developmental and/or intellectual disabilities (DD/ID) using MLPA subtelomeric specific kits (P036 /P070) and 4 of them using microarrays. We found abnormal subtelomeric CNVs in 15 patients (14.3%), including 8 patients with subtelomeric deletions at 4p/4q (53.3%). Additional genomic changes were observed at 1p36, 2q37.3, 5p15.3, 5q35.3, 8p23.3, 13q11, 14q32.3, 15q11.2, and Xq28/Yq12. This indicates the prevalence of independent deletions at 4p/4q, involving PIGG, TRIML2, and FRG1. Furthermore, we identified 15 genes with changes in copy number that contribute to neurological development and/or function, among them CRMP1, SORCS2, SLC25A4, and HELT. Our results highlight the association of genes with changes in copy number at 4p and 4q subtelomeric regions and the DD phenotype. Cytogenomic characterization of additional cases with distal deletions should help clarifying the role of subtelomeric CNVs in neurological diseases.

Meiotic and pedigree segregation analyses in carriers of t(4;8)(p16;p23.1) differing in localization of breakpoint positions at 4p subband 4p16.3 and 4p16.1

PURPOSE

The purpose of this study was to compare meiotic segregation in sperm cells from two carriers with t(4;8)(p16;p23.1) reciprocal chromosome translocations (RCTs), differing in localization of the breakpoint positions at the 4p subband-namely, 4p16.3 (carrier 1) and 4p16.1 (carrier 2)-and to compare data of the pedigree analyses performed by direct method.

METHODS

Three-color fluorescent in situ hybridization (FISH) on sperm cells and FISH mapping for the evaluation of the breakpoint positions, data from pedigrees, and direct segregation analysis of the pedigrees were performed.

RESULTS

Similar proportions of normal/balanced and unbalanced sperm cells were found in both carriers. The most common was an alternate type of segregation (about 52 % and about 48 %, respectively). Unbalanced adjacent I and adjacent II karyotypes were found in similar proportions about 15 %. The direct segregation analysis (following Stengel-Rutkowski) of the pedigree of carriers of t(4;8)(p16.1;p23.1) was performed and results were compared with the data of the pedigree segregation analysis obtained earlier through the indirect method. The probability of live-born progeny with unbalanced karyotype for carriers of t(4;8)(p16.1;p23.1) was moderately high at 18.8 %-comparable to the value obtained using the indirect method for the same carriership, which was 12 %. This was, however, markedly lower than the value of 41.2 % obtained through the pedigree segregation indirect analysis estimated for carriers of t(4;8)(p16.3;p23.1), perhaps due to the unique composition of genes present within the 4p16.1-4p 16.3 region.

CONCLUSIONS

Revealed differences in pedigree segregation analysis did not correspond to the very similar profile of meiotic segregation patterns presented by carrier 1 and carrier 2. Most probably, such discordances may be due to differences in embryo survival rates arising from different genetic backgrounds.

Prenatal diagnosis of Wolf-Hirschhorn syndrome confirmed by comparative genomic hybridization array: report of two cases and review of the literature

Wolf-Hirschhorn syndrome (WHS) is a well known genetic condition caused by a partial deletion of the short arm of chromosome 4. The great variability in the extent of the 4p deletion and the possible contribution of additional genetic rearrangements lead to a wide spectrum of clinical manifestations. The majority of the reports of prenatally diagnosed WHS cases are associated with large 4p deletions identified by conventional chromosome analysis; however, the widespread clinical use of novel molecular techniques such as array comparative genomic hybridization (a-CGH) has increased the detection rate of submicroscopic chromosomal aberrations associated with WHS phenotype. We provide a report of two fetuses with WHS presenting with intrauterine growth restriction as an isolated finding or combined with oligohydramnios and abnormal Doppler waveform in umbilical artery and uterine arteries. Standard karyotyping demonstrated a deletion on chromosome 4 in both cases [del(4)(p15.33) and del(4)(p15.31), respectively] and further application of a-CGH confirmed the diagnosis and offered a precise characterization of the genetic defect. A detailed review of the currently available literature on the prenatal diagnostic approach of WHS in terms of fetal sonographic assessment and molecular cytogenetic investigation is also provided.

Epilepsy and chromosomal abnormalities

Background

Many chromosomal abnormalities are associated with Central Nervous System (CNS) malformations and other neurological alterations, among which seizures and epilepsy. Some of these show a peculiar epileptic and EEG pattern. We describe some epileptic syndromes frequently reported in chromosomal disorders.

Methods

Detailed clinical assessment, electrophysiological studies, survey of the literature.

Results

In some of these congenital syndromes the clinical presentation and EEG anomalies seems to be quite typical, in others the manifestations appear aspecific and no strictly linked with the chromosomal imbalance. The onset of seizures is often during the neonatal period of the infancy.

Conclusions

A better characterization of the electro clinical patterns associated with specific chromosomal aberrations could give us a valuable key in the identification of epilepsy susceptibility of some chromosomal loci, using the new advances in molecular cytogenetics techniques - such as fluorescent in situ hybridization (FISH), subtelomeric analysis and CGH (comparative genomic hybridization) microarray. However further studies are needed to understand the mechanism of epilepsy associated with chromosomal abnormalities.

Separation of the PROX1 gene from upstream conserved elements in a complex inversion/translocation patient with hypoplastic left heart

Hypoplastic left heart (HLH) occurs in at least 1 in 10 000 live births but may be more common in utero. Its causes are poorly understood but a number of affected cases are associated with chromosomal abnormalities. We set out to localize the breakpoints in a patient with sporadic HLH and a de novo translocation. Initial studies showed that the apparently simple 1q41;3q27.1 translocation was actually combined with a 4-Mb inversion, also de novo, of material within 1q41. We therefore localized all four breakpoints and found that no known transcription units were disrupted. However we present a case, based on functional considerations, synteny and position of highly conserved non-coding sequence elements, and the heterozygous Prox1(+/-) mouse phenotype (ventricular hypoplasia), for the involvement of dysregulation of the PROX1 gene in the aetiology of HLH in this case. Accordingly, we show that the spatial expression pattern of PROX1 in the developing human heart is consistent with a role in cardiac development. We suggest that dysregulation of PROX1 gene expression due to separation from its conserved upstream elements is likely to have caused the heart defects observed in this patient, and that PROX1 should be considered as a potential candidate gene for other cases of HLH. The relevance of another breakpoint separating the cardiac gene ESRRG from a conserved downstream element is also discussed.

On the nosology and pathogenesis of Wolf-Hirschhorn syndrome: genotype-phenotype correlation analysis of 80 patients and literature review

Based on genotype-phenotype correlation analysis of 80 Wolf-Hirschhorn syndrome (WHS) patients, as well as on review of relevant literature, we add further insights to the following aspects of WHS: (1) clinical delineation and phenotypic categories; (2) characterization of the basic genomic defect, mechanisms of origin and familiarity; (3) identification of prognostic factors for mental retardation; (4) chromosome mapping of the distinctive clinical signs, in an effort to identify pathogenic genes. Clinically, we consider that minimal diagnostic criteria for WHS, defining a "core" phenotype, are typical facial appearance, mental retardation, growth delay and seizures (or EEG anomalies). Three different categories of the WHS phenotype were defined, generally correlating with the extent of the 4p deletion. The first one comprises a small deletion not exceeding 3.5 Mb, that is usually associated with a mild phenotype, lacking major malformations. This category is likely under-diagnosed. The second and by far the more frequent category is identified by large deletions, averaging between 5 and 18 Mb, and causes the widely recognizable WHS phenotype. The third clinical category results from a very large deletion exceeding 22-25 Mb causing a severe phenotype, that can hardly be defined as typical WHS. Genetically, de novo chromosome abnormalities in WHS include pure deletions but also complex rearrangements, mainly unbalanced translocations. With the exception of t(4p;8p), WHS-associated chromosome abnormalities are neither mediated by segmental duplications, nor associated with a parental inversion polymorphism on 4p16.3. Factors involved in prediction of prognosis include the extent of the deletion, the occurrence of complex chromosome anomalies, and the severity of seizures. We found that the core phenotype maps within the terminal 1.9 Mb region of chromosome 4p. Therefore, WHSCR-2 should be considered the critical region for this condition. We also confirmed that the pathogenesis of WHS is multigenic. Specific and independent chromosome regions were characterized for growth delay and seizures, as well as for the additional clinical signs that characterize this condition. With the exception of parental balanced translocations, familial recurrence is uncommon.