Molecular confirmation of Wolf-Hirschhorn syndrome with a subtle translocation of chromosome 4.

Wolf-Hirschhorn syndrome is a clinically recognizable, multiple congenital anomaly syndrome usually associated with terminal deletion of the short arm of chromosome 4. A girl with clinical features of Wolf-Hirschhorn syndrome did not show an obvious deletion of chromosome 4, and a molecular defect was suspected. RFLPs of genomic DNA from the proband and her parents were studied using DNA probes from the distal region of chromosome 4p. Fluorescence in situ hybridization using a cosmid p847.351 containing the fragment 847 E-C was performed to investigate the possibility of a subtle translocation. Cytogenetic analyses done on the child and on both parents did not conclusively reveal abnormalities of chromosome 4. Molecular studies using two probes mapped to distal 4p showed the absence of the maternal haplotype in the child. These findings are thus consistent with a molecular deletion of 4p and confirm the diagnosis of Wolf-Hirschhorn syndrome. Cytogenetic experiments involving fluorescence in situ hybridization showed that the mother carried a subtle translocation between chromosomes 4 and 19, 46,XX,t(4,19)(p16.3; p13.3), which resulted in an unbalanced form in the child. Chorionic villus sampling for prenatal diagnosis in a subsequent pregnancy showed the fetus to be unaffected. This provides the first evidence, in chromosome 4p, of a molecular deletion due to a subtle, inherited translocation leading to the Wolf-Hirschhorn phenotype. Such subtle translocations may become an important mechanism for some recurrent genetic defects.     

A molecular deletion of distal chromosome 4p in two families with a satellited chromosome 4 lacking the Wolf-Hirschhorn syndrome phenotype.

We report two families with a satellited chromosome 4 short arm (4ps). Satellites and stalks normally occur on the short arms of acrocentric chromosomes; however, the literature cites several reports of satellited nonacrocentric chromosomes, which presumably result from a translocation with an acrocentric chromosome. This is the first report of 4ps chromosomes. Our families are remarkable in that both unaffected and affected individuals carry the 4ps chromosome. The phenotypes observed in affected individuals, although dissimilar, were sufficient to encourage a search for a deletion of chromosome 4p. By Southern blot analysis and fluorescence in situ hybridization, a deletion of material mapping approximately 150 kb from chromosome 4pter was discovered. This deletion is notable because it does not result in the Wolf-Hirschhorn syndrome and can result in an apparently normal phenotype. We speculate that homology between subterminal repeat sequences on 4p and sequences on the acrocentric short arms may explain the origin of the rearrangement and that position effect may play a role in the expression of the abnormal phenotype.     

Molecular definition of the smallest region of deletion overlap in the Wolf-Hirschhorn syndrome.

Wolf-Hirschhorn syndrome (WHS), associated with a deletion of chromosome 4p, is characterized by mental and growth retardation and typical facial dysmorphism. A girl with clinical features of WHS was found to carry a subtle deletion of chromosome 4p. Initially suggested by high-resolution chromosome analysis, her deletion was confirmed by fluorescence in situ hybridization (FISH) with cosmid probes, E13 and Y2, of D4S113. To delineate this 4p deletion, we performed a series of FISH and pulsed-field gel electrophoresis analyses by using probes from 4p16.3. A deletion of approximately 2.5 Mb with the breakpoint at approximately 80 kb distal to D4S43 was defined in this patient and appears to be the smallest WHS deletion so far identified. To further refine the WHS critical region, we have studied three unrelated patients with presumptive 4p deletions, two resulting from unbalanced segregations of parental chromosomal translocations and one resulting from an apparently de novo unbalanced translocation. Larger deletions were identified in two patients with WHS. One patient who did not clinically present with WHS had a smaller deletion that thus eliminates the distal 100-300 kb from the telomere as being part of the WHS region. This study has localized the WHS region to approximately 2 Mb between D4S43 and D4S142.     

Discrepancies in cytogenetic results between different tissues in two fetuses with Wolf- Hirschhorn syndrome

Discrepant unbalanced structural chromosome aberrations between placental and fetal tissue, both involving the short arm of chromosome 4, were found in two human fetuses affected with Wolf-Hirschhorn syndrome. In the first instance, placental chromosome examination revealed a del(4) (p14), whereas fetal fibroblast chromosomes showed an unbalanced der(4)t(4;13)(p14;q11) translocation. In the second instance, placental karyotyping revealed a 4p+ chromosome, while amniocytes showed a submicroscopic deletion at 4p16.3. Since confirmation of structural aberrations from placental tissue is mostly not sought if the phenotype of the fetus is abnor- mal, discrepancies between karyotypes obtained from placental tissue and amniocytes or fetal tissues might be more frequent than the rare reports published so far would suggest. It is unclear whether the simple deletion or the more complex rearrangement is the primary aberration from which the other derived. Structural chromosome aberrations often have a much more complex mechanism of formation than the end product would suggest, and secondary rearrangements of a given aberration in the zygote are more frequent than expected.     

Cytogenetic genotype-phenotype studies: improving genotyping, phenotyping and data storage

High-resolution molecular cytogenetic techniques such as genomic array CGH and MLPA detect submicroscopic chromosome aberrations in patients with unexplained mental retardation. These techniques rapidly change the practice of cytogenetic testing. Additionally, these techniques may improve genotype-phenotype studies of patients with microscopically visible chromosome aberrations, such as Wolf-Hirschhorn syndrome, 18q deletion syndrome and 1p36 deletion syndrome. In order to make the most of high-resolution karyotyping, a similar accuracy of phenotyping is needed to allow researchers and clinicians to make optimal use of the recent advances. International agreements on phenotype nomenclature and the use of computerized 3D face surface models are examples of such improvements in the practice of phenotyping patients with chromosomal anomalies. The combination of high-resolution cytogenetic techniques, a comprehensive, systematic system for phenotyping and optimal data storage will facilitate advances in genotype-phenotype studies and a further deconstruction of chromosomal syndromes. As a result, critical regions or single genes can be determined to be responsible for specific features and malformations.     

Wolf-Hirschhorn syndrome: A case demonstrated by a cytogenetic study

We present a case with a 4p terminal deletion, evidenced in GTG-banded chromosome study. Phenotypic signs described in the classical Wolf-Hirschhorn syndrome were found on clinical examination of our patient.     

Cytogenetic findings in a prospective series of patients with DiGeorge anomaly.

High-resolution cytogenetics analysis of peripheral blood lymphocytes was done prospectively on 27 of 28 patients with features of DiGeorge anomaly. Twenty-two patients (81%) had normal chromosome studies with no detectable deletion in chromosome 22. Five patients (18%) had demonstrable chromosome abnormalities. Three patients had monosomy 22q11, one due to a 4q;22q translocation, one due to a 20q;22q translocation, and one due to an interstitial deletion of 22q11. One patient had monosomy 10p13, and one patient had monosomy 18q21.33, although the latter had subsequent resolution of T-cell defects. These findings are consistent with the heterogeneity of DiGeorge anomaly but confirm the association with monosomy 22q11 in some cases. However, monosomy 10p13 may also lead to this phenotype. Because of these associated chromosome findings, cytogenetic analyses should be done on patients with suspected DiGeorge anomaly. This is particularly important since many of the abnormalities involving chromosome 22 are translocations that can be familial with a higher recurrence risk. Since only one subtle, interstitial deletion of chromosome 22 was observed, it is not clear whether high-resolution cytogenetic analysis is cost beneficial for all such patients.     

Interstitial deletion of the short arm of chromosome 4. A phenotype distinct from the Wolf-Hirschhorn syndrome

In this paper we report a 3-month-old male newborn with marked hypotonia and an interstitial deletion of the short arm of chromosome 4 but with preservation of the 4p16 band (karyotype 46,XY,del(4)(pter----p15.3::p14----cen----qter). In contrast to patients with a pure 4p16 deletion this patient presented dysmorphic stigmata which were much more discrete than those found in the typical Wolf-Hirschhorn syndrome.     

Detection of deletions and cryptic translocations in Miller-Dieker syndrome by in situ hybridization.

Fluorescence in situ hybridization (FISH) using two cosmid probes (41A and P13) from the Miller-Dieker syndrome (MDS) critical region in 17p13.3 was performed in a blinded comparison of three MDS patients with submicroscopic deletions and in four normal relatives used as controls. The controls showed both chromosome 17 homologues labeled in 85%-95% of cells, while each patient showed only one homologue labeled in 75%-80% of cells. Two MDS patients with cryptic translocations were also studied. In one case, a patient and her mother had the same der(17) (p+), but the reciprocal product of the translocation could not be identified in the mother by G-banding (i.e., it was a "half-cryptic" translocation). FISH revealed a 3q;17p translocation. The other case involved a patient with apparently normal karyotype. Because a large molecular deletion was found, a translocation involving two G-negative telomeres (i.e., a "full-cryptic" translocation) was postulated. FISH studies on her father and normal brother showed an 8q;17p translocation. These studies demonstrate that in situ hybridization is an efficient method for deletion detection in Miller-Dieker syndrome. More important, parental studies by FISH on patients demonstrating molecular deletions and a normal karyotype may identify cryptic translocation events, which cannot be detected by other molecular genetic strategies. Similar in situ strategies for deletion detection can be developed for other microdeletion syndromes, such as Prader-Willi/Angelman syndrome or DiGeorge syndrome.     

Localization of the D5 dopamine receptor gene to human chromosome 4p15.1-p15.3, centromeric to the Huntington's disease locus.

Genes encoding G-protein-coupled receptors, including dopamine, serotonin, muscarinic cholinergic, and adrenergic receptors, play an important role in neurotransmission and may be involved in the pathophysiology of diseases such as Alzheimer's disease, Parkinson's disease, or Huntington's disease (HD). We mapped the gene encoding the D5 dopamine receptor (DRD5) to human chromosome 4p, an area implicated in HD and the Wolf-Hirschhorn syndrome, using gene-specific amplification with the polymerase chain reaction on a panel of somatic cell hybrids carrying different human chromosomes. Further localization of the DRD5 gene was carried out through the isolation and analysis of yeast artificial chromosomes, fluorescence in situ suppression hybridization to human metaphase chromosomes, and analysis of a panel of somatic cell hybrids subdividing human chromosome 4 into nine regions. The human DRD5 gene is located at 4p15.1-p15.33, centromeric to the location of the Huntington's disease locus although not in the obligate area containing the HD gene. The localization of the DRD5 gene to 4p15.1-p15.33 suggests the possibility that cis-position effects could be responsible for the altered D1-type dopamine receptor number observed in HD tissues or that the DRD5 gene could be a candidate for some of the abnormalities associated with the Wolf-Hirschhorn syndrome.     

Familial DiGeorge syndrome and associated partial monosomy of chromosome 22

Summary Partial monosomy of 22q due to an unbalanced 4;22 translocation was seen in a 2-month-old male with Type I truncus arterious, dysmorphic features, and T-cell abnormalities. The family history revealed a previous sib with Type I truncus arteriosus, thymic aplasia, and parathyroid hypoplasia noted on postmortem examination, consistent with DiGeorge syndrome. Evaluation of the asymptomatic mother of these two patients revealed partial T-cell deficiency and the same unbalanced translocation with deletion of proximal 22qll. These findings provide further evidence that some cases of complete or partial DiGeorge syndrome are associated with monosomy of the proximal long arm of chromosome 22, and they may explain many, if not all, familial cases of the syndrome.Supported in part by National Foundation-March of Dimes Grant No. 2-161/C-331. Funds from the Texas Department of Health through PL94-278 National Genetic Diseases Act, from the Robert J. Kleberg, Jr. Center for Human Genetics, and USPHS Grant No. RR-05425.     

Molecular, cytogenetic, and clinical investigations of Prader-Willi syndrome patients.

Thirty-seven patients presenting features of the Prader-Willi syndrome (PWS) have been examined using cytogenetic and molecular techniques. Clinical evaluation showed that 29 of these patients fulfilled diagnostic criteria for PWS. A deletion of the 15q11.2-q12 region could be identified molecularly in 21 of these cases, including several cases where the cytogenetics results were inconclusive. One clinically typical patient is deleted at only two of five loci normally included in a PWS deletion. A patient carrying a de novo 13;X translocation was not deleted for the molecular markers tested but was clinically considered to be "atypical" PWS. In addition, five cases of maternal heterodisomy and two of isodisomy for 15q11-q13 were observed. All of the eight patients who did not fulfill clinical diagnosis of PWS showed normal maternal and paternal inheritance of chromosome 15 markers; however, one of these carried a ring-15 chromosome. A comparison of clinical features between deletion patients and disomy patients shows no significant differences between the two groups. The parental ages at birth of disomic patients were significantly higher than those for deletion patients. As all typical PWS cases showed either a deletion or disomy of 15q11.2-q12, molecular examination should provide a reliable diagnostic tool. As the disomy patients do not show either any additional or more severe features than typical deletion patients do, it is likely that there is only one imprinted region on chromosome 15 (within 15q11.2-q12).     

The etiology of Wolf-Hirschhorn syndrome

Wolf-Hirschhorn syndrome (WHS) is defined by a collection of core characteristics, which include mental retardation, epilepsy, growth delay and cranio-facial dysgenesis. The disorder is caused by sub-telomeric deletions in the short arm of chromosome 4. The severity of the core characteristics is highly variable, and additional problems, including midline fusion defects, occur at lower frequency. Only one gene, WHSC1, is deleted in every case. However, recent evidence, from patient studies and mouse models, indicates that deletion of WHSC1 alone is insufficient for full-blown WHS. Instead a model is emerging in which deletion of WHSC1 is essential for pathogenesis, but deletion of linked genes contributes to both the severity of the core characteristics and the presence of the additional syndromic problems. In this article, we outline the progress being made in patient studies and in the development of mouse models, and relate the implications of this work for a broad group of sub-telomeric deletion syndromes.     

Familial cryptic translocation resulting in Angelman syndrome:implications for imprinting or location of the Angelman gene?

Angelman syndrome (AS) is associated with a loss of maternal genetic information, which typically occurs as a result of a deletion at 15q11-q13 or paternal uniparental disomy of chromosome 15. We report a patient with AS as a result of an unbalanced cryptic translocation whose breakpoint, at 15q11.2, falls within this region. The proband was diagnosed clinically as having Angelman syndrome, but without a detectable cytogenetic deletion, by using high-resolution G-banding. FISH detected a deletion of D15S11 (IR4-3R), with an intact GABRB3 locus. Subsequent studies of the proband's mother and sister detected a cryptic reciprocal translocation between chromosomes 14 and 15 with the breakpoint being between SNRPN and D15S10 (3- 21). The proband was found to have inherited an unbalanced form, being monosomic from 15pter through SNRPN and trisomic for 14pter to 14q11.2. DNA methylation studies showed that the proband had a paternal-only DNA methylation pattern at SNRPN, D15S63 (PW71), and ZNF127. The mother and unaffected sister, both having the balanced translocation, demonstrated normal DNA methylation patterns at all three loci. These data suggest that the gene for AS most likely lies proximal to D15S10, in contrast to the previously published position, although a less likely possibility is that the maternally inherited imprinting center acts in trans in the unaffected balanced translocation carrier sister.     

Microarray-based comparative genomic hybridization analysis of Wolf-Hirschhorn syndrome in a fetus with deletion of 4p15.3 to 4pter

BACKGROUND: Wolf-Hirschhorn syndrome (WHS), caused by the deletion of a segment in chromosome 4, is characterized by mental and developmental defects. Clinical manifestations of WHS include intrauterine growth restriction, failure to thrive in the neonatal period that is present simultaneously with hypotonia, typical "Greek helmet" facial appearance, cleft lip and palate, mental deficiency, and seizures. CASE: We present a case of WHS with prenatal conventional cytogenetics of 46,XY,der(4)t(4;13)(p15.3;p11.2)pat. High-resolution mapping using microarray-based comparative genomic hybridization (array-CGH), including Affymetrix 10K arrays and cDNA microarrays, confirmed the loss of genes in the deleted region. CONCLUSIONS: The correlation between these candidate genes and the phenotypes of WHS may expand our understanding of the defective development caused by 4p deletion.     

No significant effect of monosomy for distal 21q22.3 on the Down syndrome phenotype in “Mirror” duplications of chromosome 21

Three Down syndrome patients for whom karyotypic analysis showed a "mirror" (reverse tandem) duplication of chromosome 21 were studied by phenotypic, cytogenetic, and molecular methods. On high-resolution R-banding analysis performed in two cases, the size of the fusion 21q22.3 band was apparently less than twice the size of the normal 21q22.3, suggesting a partial deletion of distal 21q. The evaluation of eight chromosome 21 single-copy sequences of the 21q22 region--namely, SOD1, D21S15, D21S42, CRYA1, PFKL, CD18, COL6A1, and S100B--by a slot blot method showed in all three cases a partial deletion of 21q22.3 and partial monosomy. The translocation breakpoints were different in each patient, and in two cases the rearranged chromosome was found to be asymmetrical. The molecular definition of the monosomy 21 in each patient was, respectively, COL6A1-S100B, CD18-S100B, and PFKL-S100B. DNA polymorphism analysis indicated in all cases a homozygosity of the duplicated material. The duplicated region was maternal in two patients and paternal in one patient. These data suggest that the reverse tandem chromosomes did not result from a telomeric fusion between chromosomes 21 but from a translocation between sister chromatids. The phenotypes of these patients did not differ significantly from that of individuals with full trisomy 21, except in one case with large ears with an unfolded helix. The fact that monosomy of distal 21q22.3 in these patients resulted in a phenotype very similar to Down syndrome suggests that the duplication of the genes located in this part of chromosome 21 is not necessary for the pathogenesis of the Down syndrome features observed in these patients, including most of the facial and hand features, muscular hypotonia, cardiopathy of the Fallot tetralogy type, and part of the mental retardation.     

Subregional assignment of the linked marker G8 (D4S10) for Huntington disease to chromosome 4p16.1-16.3.

The linked DNA marker for Huntington disease has recently been mapped to the short arm of chromosome 4 by somatic cell hybridization studies. Southern blot analysis of DNA from patients with Wolf-Hirschhorn syndrome (WHS) has suggested that the linked marker maps within the terminal 4p16 band. We have now accomplished subregional assignment of G8 (D4S10) to 4p16.1-16.3 using in situ hybridization techniques on two patients with nonoverlapping interstitial deletions of 4p. The mapping of G8 (D4S10) to a region deleted in patients with WHS will allow the application of new strategies for detecting DNA sequences closer to the locus for Huntington disease.     

Chromosome 15 abnormalities and the Prader-Willi syndrome: a follow-up report of 40 cases.

High-resolution chromosome analysis and multiple banding techniques were performed on blood samples from 40 patients with Prader-Willi syndrome (PWS) as a follow-up to our recent report in which we found interstitial deletions of 15q in four of five patients with this syndrome. Of the 40 new patients, 19 had interstitial del(15q), one had an apparently balanced 15;15 translocation, and one was mos46,XX/47,XX+idic(15) (pter leads to q11::q11 leads to pter). These data confirm our previous report and demonstrate that half of all patients with the clinical diagnosis of PWS have chromosome abnormalities involving chromosome 15 detectable by high-resolution methods. Although the majority of these involve a specific deletion of bands 15q11-q12, other alterations of chromosome 15 may be present.     

A neocentromere derived from a supernumerary marker deleted from the long arm of chromosome 6

Parental chromosome studies were referred to us after initial finding of a balanced translocation involving chromosomes 4 and 15 in their phenotypically abnormal male child (cytogenetic analysis was done at another laboratory). In addition to the same 4;15 translocation, the father also had an interstitial deletion of the long arm of one chromosome 6 and a marker chromosome. In this article, we report a neocentromere on this marker, which was determined to be composed of chromosome 6 material by FISH. The child's karyotype was re-interpreted to be unbalanced due to the presence of the abnormal chromosome 6, but without the marker. The clinical phenotype associated with the interstitial deletion of chromosome 6 is also reported.