Paternal origin of the chromosomal deletion resulting in Wolf-Hirschhorn syndrome

Investigation of parent-of-origin effect in comitant strabismus using MOD score analysis

PURPOSE

Comitant strabismus is a common pediatric ophthalmic disorder with both genetic and non-genetic factors contributing to its etiology. The aim of the current study is to investigate the phenomenon of a parent-of-origin effect, genomic imprinting, as a possible mode of inheritance in comitant strabismus.

METHODS

We performed parametric genome-wide MOD score (model-maximized LOD score) linkage analysis, incorporating imprinting effects, for 382 microsatellite markers in a sample of 258 individuals (117 males and 141 females) from 55 Japanese families with comitant strabismus. We included individuals as affected patients if they presented with comitant esotropia or exotropia based on ophthalmic examination, history taking, or analysis of medical records.

RESULTS

Significant or suggestive linkage to comitant strabismus with evidence of maternal or paternal imprinting was detected at D4S1575 (4q28.3), D7S486 (7q31.2), D11S1320 (11q24.2), D12S324 (12q24.32), and D19S420 (19q13.11). Using the MOD score approach, we found new evidence of linkage to comitant strabismus at three loci on chromosomes 6q26 (MOD(imp)=MOD(reg)=3.75), 12q24.32 (MOD(imp)=3.36), and 19q13.11 (MOD(imp)=3.79).

CONCLUSIONS

The results suggest that the parent-of-origin effect may play a role in the etiology of comitant strabismus.

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

The basic genomic defect in Wolf-Hirschhorn syndrome (WHS), including isolated 4p deletions and various unbalanced de novo 4p;autosomal translocations and above all t(4p;8p), is heterogeneous. Olfactory receptor gene clusters (ORs) on 4p were demonstrated to mediate a group of WHS-associated t(4p;8p)dn translocations. The breakpoint of a 4-Mb isolated deletion was also recently reported to fall within the most distal OR. However, it is still unknown whether ORs mediate all 4p-autosomal translocations, or whether they are involved in the origin of isolated 4p deletions. Another unanswered question is whether a parental inversion polymorphism on 4p16 can act as predisposing factor in the origin of WHS-associated rearrangements. We investigated the involvement of the ORs in the origin of 73 WHS-associated rearrangements. No hotspots for rearrangements were detected. Breakpoints on 4p occurred within the proximal or the distal olfactory receptor gene cluster in 8 of 73 rearrangements (11%). These were five t(4p;8p) translocations, one t(4p;7p) translocation and two isolated terminal deletions. ORs were not involved in one additional t(4p;8p) translocation, in a total of nine different 4p;autosomal translocations and in the majority of isolated deletions. The presence of a parental inversion polymorphism on 4p was investigated in 30 families in which the 4p rearrangements, all de novo, were tested for parental origin (7 were maternal and 23 paternal). It was detected only in the mothers of 3 t(4p;8p) cases. We conclude that WHS-associated chromosome changes are not usually mediated by low copy repeats. The 4p16.3 inversion polymorphism is not a risk factor for their origin.

Wolf-Hirschhorn Syndrome: Report of two Cases in Bosnia and Herzegovina

Wolf-Hirschhorn syndrome (WHS) is a rare developmental disorder caused by a partial deletion of the short arm of chromosome 4 (4p-). The main phenotypic characteristics of WHS are: intrauterine growth retardation, mental retardation, typical facial dysmorphism, microcephaly and midline fusion defects (cleft lip or palate, cardiac septal defects). Other abnormalities, such as agenesis of the corpus callosum, dysplastic kidneys, iris coloboma and skeletal abnormalities have occasionally been described.

We describe two female newborn babies with a 4p deletion, who have a majority of the main phenotypic features of WHS. Prenatal diagnosis of the syndrome is very important, because dysmorphologic features are associated with profound mental retardation. Postnatal recognition of the syndrome requires genetic counseling of the parents and supportive multidisciplinary treatment.

Multiple mechanisms are implicated in the generation of 5q35 microdeletions in Sotos syndrome

BACKGROUND

Sotos syndrome is characterised by learning difficulties, overgrowth, and a typical facial appearance. Microdeletions at 5q35.3, encompassing NSD1, are responsible for approximately 10% of non-Japanese cases of Sotos. In contrast, a recurrent approximately 2 Mb microdeletion has been reported as responsible for approximately 50% of Japanese cases of Sotos.

METHODS

We screened 471 cases for NSD1 mutations and deletions and identified 23 with 5q35 microdeletions. We investigated the deletion size, parent of origin, and mechanism of generation in these and a further 10 cases identified from published reports. We used "in silico" analyses to investigate whether repetitive elements that could generate microdeletions flank NSD1.

RESULTS

Three repetitive elements flanking NSD1, designated REPcen, REPmid, and REPtel, were identified. Up to 18 cases may have the same sized deletion, but at least eight unique deletion sizes were identified, ranging from 0.4 to 5 Mb. In most instances, the microdeletion arose through interchromosomal rearrangements of the paternally inherited chromosome.

CONCLUSIONS

Frequency, size, and mechanism of generation of 5q35 microdeletions differ between Japanese and non-Japanese cases of Sotos. Our microdeletions were identified from a large case series with a broad range of phenotypes, suggesting that sample selection variability is unlikely as a sole explanation for these differences and that variation in genomic architecture might be a contributory factor. Non-allelic homologous recombination between REPcen and REPtel may have generated up to 18 microdeletion cases in our series. However, at least 15 cannot be mediated by these repeats, including at least seven deletions of different sizes, implicating multiple mechanisms in the generation of 5q35 microdeletions.

Parental and chromosomal origin of unbalanced de novo structural chromosome abnormalities in man

We report the parental origin, and where possible the chromosomal origin of 115 de novo unbalanced structural chromosome abnormalities detectable by light microscopy. These consisted of 39 terminal deletions, 35 interstitial deletions, 8 rings, 12 duplications and 21 unbalanced translocations. In all categories the majority of abnormalities were of paternal origin, although the proportions varied from a high of 84% in the interstitial deletions and rings to a low of 58% in the duplications. Among the interstitial deletions and duplications, there were approximately equal numbers of intra- and interchromosomal abnormalities, while the majority of unbalanced translocations were isodisomic for the duplicated chromosome. The examination of the parental ages in the four main classes of abnormality showed terminal deletions of maternal origin to be associated with a significantly reduced maternal age. Thus, there is a clear propensity for structural chromosome abnormalities to occur in male germ cells, although the chromosomal origin seems similar irrespective of the parental origin.

Molecular screening for microdeletions at 9p22-p24 and 11q23-q24 in a large cohort of patients with trigonocephaly

Trigonocephaly is a rare form of craniosynostosis characterized by the premature closure of the metopic suture. To contribute to a better understanding of the genetic basis of metopic synostosis and in an attempt to restrict the candidate regions related to metopic suture fusion, we studied 76 unrelated patients with syndromic and non-syndromic trigonocephaly. We found a larger proportion of syndromic cases in our population and the ratio of affected male to female was 1.8 : 1 and 5 : 1 in the non-syndromic and syndromic groups, respectively. A microdeletion screening at 9p22-p24 and 11q23-q24 was carried out for all patients and deletions in seven of them were detected, corresponding to 19.4% of all syndromic cases. Deletions were not found in non-syndromic patients. We suggest that a molecular screening for microdeletions at 9p22-p24 and 11q23-q24 should be offered to all syndromic cases with an apparently normal karyotype because it can potentially elucidate the cause of trigonocephaly in this subset of patients. We also suggest that genes on the X-chromosome play a major role in syndromic trigonocephaly.

Prenatal diagnosis of monosomy 4p14→pter and trisomy 11q25→qter: clinical presentations and outcomes

We present the case of a pregnant woman with low free beta-HCG in maternal serum Down syndrome screening that led to prenatal diagnosis of a fetus with 46,XY,der(4)t(4;11)(p14; q25). This chromosomal aneuploidy resulted from unbalanced segregation of a paternal balanced translocation, t(4;11)(p14;q25). Prenatal ultrasound revealed intrauterine growth restriction, cleft lip and palate, a thick nuchal fold, a single umbilical artery, and pyelectasis. Array-based comparative genomic hybridization and short tandem repeat markers further located the exact breakpoint of translocation. The woman had her pregnancy terminated at 23 weeks of gestational age. The proband had general appearance of Wolf-Hirschhorn syndrome and some unique findings, including single umbilical artery, severe immunoglobulin deficiency, scalp defect, and underlying bony defect. Our case underscores the importance of fetal karyotyping when low maternal serum free beta-HCG is found. It also adds information on the fetal presentations of monosomy 4p14-->pter and trisomy 11q25-->qter.

Population data suggest that deletions of 1p36 are a relatively common chromosome abnormality

Monosomy 1p36 is a relatively common chromosome deletion. Deletion of this chromosome band can be difficult to visualize using routine cytogenetic banding techniques. The use of fluorescence in situ hybridization (FISH) with telomere region-specific probes has aided in the diagnosis of patients. In this study we ascertained 62 patients with deletions of 1p36 from 61 families and collected information regarding previous chromosome analyses, mode of ascertainment, clinical indication, age at diagnosis, and parental ages. The majority of deletions occur on the maternally derived chromosome. We identified terminal deletions, interstitial deletions, derivative chromosomes, and complex rearrangements. We correlated the type of rearrangement with the parental origins. Almost 50% of the patients had at least one chromosome analysis interpreted as normal. Retrospectively, 98% of deletions could be identified by routine chromosome analysis with careful attention to chromosome 1p36. Clinical indications were variable, with developmental delay/mental retardation being the most common. Increased maternal serum alpha fetoprotein (MSAFP) was detected in four of the five prenatally diagnosed cases. Maternal age at the time of birth of the affected child was significantly lower than the general United States population mean. We suggest a multistep approach for the diagnosis and clinical evaluation in cases of monosomy 1p36.

Are children of older fathers at risk for genetic disorders?

Genetic risks related to paternal age should be of interest to clinical andrologists counselling older men who wish to father a child. Theoretically, the number of (pre-meiotic) mitotic cell divisions during spermatogenesis and their remarkable increase with ageing compared with oogenesis would be in favour of genetic risks for the offspring of older men. But for numerical and structural chromosomal anomalies, such an influence of paternal age has not been found. However, in several autosomal dominant disorders affecting three specific genes (fibroblast growth factor receptor 2 and 3, RET proto-oncogene) the risk for a child to be affected increases with paternal age at time of birth. For other autosomal dominant -X chromosomal dominant or recessive disorders, the available data are sufficient to support the concept of a positive relationship between paternal age and de novo gene mutations. Studies analysing gene sequences of affected children and their parents would allow further evaluation of this topic. The impact of paternal age on disorders with a complex genetic background, however, is a matter of debate. A significant effect of paternal age could not be shown for nonfamilial Alzheimer's disease, congenital heart defects, nonfamilial schizophrenia, acute lymphoblastic leukaemia or prostate cancer.

Molecular characterisation of the 22q13 deletion syndrome supports the role of haploinsufficiency of SHANK3/PROSAP2 in the major neurological symptoms

METHODS

The 22q13 deletion syndrome (MIM 606232) is characterised by moderate to profound mental retardation, delay/absence of expressive speech, hypotonia, normal to accelerated growth, and mild dysmorphic features. We have determined the deletion size and parent of origin in 56 patients with this syndrome.

RESULTS

Similar to other terminal deletion syndromes, there was an overabundance of paternal deletions. The deletions vary widely in size, from 130 kb to over 9 Mb; however all 45 cases that could be specifically tested for the terminal region at the site of SHANK3 were deleted for this gene. The molecular structure of SHANK3 was further characterised. Comparison of clinical features to deletion size showed few correlations. Some measures of developmental assessment did correlate to deletion size; however, all patients showed some degree of mental retardation and severe delay or absence of expressive speech, regardless of deletion size.

CONCLUSION

Our analysis therefore supports haploinsufficiency of the gene SHANK3, which codes for a structural protein of the postsynaptic density, as a major causative factor in the neurological symptoms of 22q13 deletion syndrome.

Preferential paternal origin of microdeletions caused by prezygotic chromosome or chromatid rearrangements in Sotos syndrome

Sotos syndrome (SoS) is characterized by pre- and postnatal overgrowth with advanced bone age; a dysmorphic face with macrocephaly and pointed chin; large hands and feet; mental retardation; and possible susceptibility to tumors. It has been shown that the major cause of SoS is haploinsufficiency of the NSD1 gene at 5q35, because the majority of patients had either a common microdeletion including NSD1 or a truncated type of point mutation in NSD1. In the present study, we traced the parental origin of the microdeletions in 26 patients with SoS by the use of 16 microsatellite markers at or flanking the commonly deleted region. Deletions in 18 of the 20 informative cases occurred in the paternally derived chromosome 5, whereas those in the maternally derived chromosome were found in only two cases. Haplotyping analysis of the marker loci revealed that the paternal deletion in five of seven informative cases and the maternal deletion in one case arose through an intrachromosomal rearrangement, and two other cases of the paternal deletion involved an interchromosomal event, suggesting that the common microdeletion observed in SoS did not occur through a uniform mechanism but preferentially arose prezygotically.

Prenatal diagnosis of Wolf-Hirschhorn syndrome (4p-) in association with congenital hypospadias and foot deformity

BACKGROUND: Wolf-Hirschhorn syndrome is caused by distal deletion of the short arm of chromosome 4 (4p-). We report a case in which intrauterine growth restriction, hypospadias and foot deformity were detected by prenatal ultrasound examination at 29 weeks of gestation. CASE PRESENTATION: A 31-year-old gravida 2 partus 1 woman was referred at 29 weeks' gestation with suspicion of intrauterine growth restriction. Sonographic examination revealed deformity of the right lower limb and undescended testes with an irregular distal penis. A cordocentesis was performed and chromosome analysis revealed a 46,XY,del(4)(p14) karyotype. CONCLUSION: The prenatal detection of intrauterine growth restriction, hypospadias and foot deformity should lead doctors to suspect the presence of Wolf-Hirschhorn syndrome.

Preferential loss of the paternal alleles in the 18q- syndrome

Individuals with the 18q- syndrome have variable deletions from the long arm of chromosome 18. They also exhibit a highly variable phenotype. To correlate genotype with phenotype accurately, extensive molecular and phenotypic analyses are needed on each affected individual. As a part of this analysis, we have determined the parental origin of the deleted chromosome in 34 individuals with the 18q- syndrome. We have found that 85% of the de novo deletions are paternal in origin. The percentage of fathers of individuals with paternally derived deletions who were > 30 years old was (not significantly) greater than that of the general population. The mothers of individuals with maternally derived deletions were near an average age for childbearing compared to the general population. Individuals with maternally derived terminal deletions had breakpoints as varied as those with paternally derived deletions. These results are consistent with the hypothesis that the reduced incidence of maternally derived deletions is not due to reduced viability, since individuals with large maternally derived deletions of chromosome 18q were found. We hypothesize that the prevalence of paternally derived deletions is due to an increased frequency of chromosome breakage in male germ cells. These results are consistent with results observed in other segmental aneusomies in which there is a high incidence of paternally derived deletions.

Allelic loss of the short arm of chromosome 4 in neuroblastoma suggests a novel tumour suppressor gene locus

Neuroblastoma is a childhood neural crest tumour, genetically characterized by frequent deletions of the short arm of chromosome 1 and amplification of N-myc. Here we report the first evidence for a neuroblastoma tumour suppressor locus on 4pter. Cytogenetically we demonstrated rearrangements of 4p in 7 out of 26 evaluable tumours (27%). Subsequent analysis of loss of heterozygosity (LOH) by Southern blotting revealed allelic loss of 4p in 16/82 (19.5%) informative neuroblastomas. Taken together cytogenetic and Southern blot analyses showed loss of 4p in 20/86 neuroblastomas analysed (23%). The common deleted region was bordered by the probe D4S123 and encompassed the distal 34 cM of 4p. We found no evidence for genomic imprinting of the 4p locus as the 4p alleles lost in the tumours were of random maternal and paternal origin. LOH4p was found at all disease stages and in every age group. Furthermore LOH4p was present both in cases with and without LOH1p and amplification of N-myc.

Parental origin of De Novo chromosome 9 deletions in del(9p) syndrome

Parental origin of de novo deletions in the short arm of chromosome 9 in patients with a clinical diagnosis of del(9p) syndrome was assessed in 13 patients using polymerase chain reaction (PCR) analysis of highly polymorphic dinucleotide repeat microsatellite markers located in the putative deleted region. The deletion was found to be of paternal origin in 9 cases and of maternal origin in the remaining 4 cases, suggesting that the molecular event resulting in the deletion occurs in both male and female gametogenesis and that genomic imprinting does not appear to play a role in the pathogenesis of del(9p) syndrome.

A patient with Wolf-Hirschhorn syndrome originating from translocation t(4;8) (p16.3;q24.3)pat

We present here a 7 year old girl with the clinical signs of Wolf-Hirschhorn syndrome (WHS). Only on high resolution banding was a deletion of 4p16.3 suspected in both the proband and the father. Further studies using simultaneous R banding and FISH, with cosmid probe pc847.351 containing the mildly repetitive fragment 847-EC, confirmed the diagnosis and showed a paternal balanced translocation t(4;8)(p16.3;q24.3).

FISH detection of Wolf-Hirschhorn syndrome: exclusion of D4F26 as critical site

Wolf-Hirschhorn syndrome (WHS) is due to a deletion in the terminal band of 4p16.3. Among loci that have been involved in deletions are D4S98, D4S95, D4S125, D4F26, as shown by PCR typing, Southern blot hybridization, and/or fluorescent in situ hybridization (FISH). Currently, FISH detection of WHS is predicted upon the deletion of the D4F26 locus with failure to hybridize to pC847.351, a commercially available cosmid probe. A WHS patient is shown to have an interstitial deletion, by hemizygosity at D4S98 and D4S95 but not at D4F26. This suggests that the tip of 4p, specifically D4F26, is not a critical deletion site for WHS.

Molecular characterisation of chromosome 4p deletions resulting in Wolf-Hirschhorn syndrome

We present three patients with Wolf-Hirschhorn syndrome with small cytogenetic deletions of 4p16. One case is a de novo translocation and two cases represent de novo deletions. Using molecular techniques we determined the extent of these deletions and attempted to ascertain parental origin. Case 1 had a deletion of 4p16.3 with a breakpoint proximal to D4S10, case 2 had a larger deletion including D4S62 in 4p16.2, and case 3 had the largest deletion which included D4S240, but not the Raf2 locus in 4p16.1. The parental origin of the deletion in case 3 was paternal; the other two cases were indeterminable. Our results show that these three deletions include the currently proposed Wolf-Hirschhorn syndrome critical region within the most distal 2 Mb of 4p16.3 and offer supportive evidence for continuous terminal deletions.

Parental origin of chromosome 4p deletion in Wolf-Hirschhorn syndrome

We report on molecular studies in 7 patients with Wolf-Hirschhorn syndrome (WHC) not showing an obvious chromosome 4p deletion. Analysis of a set of polymorphic probes mapping in the 4p16.3 region showed the absence of paternal haplotypes in 5 cases, and maternal haplotypes in 2. These observations corroborate evidence for preferential paternal origin of the de novo 4p chromosome deletion. The overall results of molecular studies suggest that the preponderance of paternally derived WHC could be due, rather than to imprinting of this region, to an excess of structural rearrangements in the male meiosis, related to differences between the mechanisms of sperm and egg production.

Two sibs with different phenotypes due to adjacent-1 segregation of a subtle translocation t(4;5)(p16.3;p15.3)mat

High-resolution chromosome banding and in situ hybridization with combined cosmid and alphoid sequence probes were used to delineate a very small reciprocal translocation in a mother and her two children. The first child has a 46,XX,der(4)t(4;5)(p16.3;p15.3)mat and thus has a deletion of 4p16.3-->pter and a duplication of 5p15.3-->pter (most likely 5p15.31-->pter). Clinical findings include marked growth retardation, developmental delay, seizure disorder, microcephaly, unruly hair, broad nasal tip, downturned mouth, narrow palate, 11 pairs of ribs, mild right club foot, and a deep sacral dimple. Thus, this child has only a few non-specific manifestations of Wolf-Hirschhorn syndrome. The second child has a 46,XY,der(5)t(4;5)(p16.3;p15.3)mat; thus a deletion of 5p15.3-->pter and a duplication of 4p16.3-->pter. He has failure to thrive, developmental delay, microcephaly, sparse hair, horizontal nystagmus, short upturned nose with flared nostrils, thin lips with overhanging upper lip, long fingers and toes, and hypertonicity. Findings in the second patient are not suggestive of cri du chat syndrome (del 5p). The mother is phenotypically normal. This translocation will be useful in mapping genes and markers on the 4p and 5p chromosomal regions.

Characterization of a duplication in the terminal band of 4p by molecular cytogenetics

An infant with multiple anomalies including small head, large apparently low-set ears, beaked nose, micrognathia, choanal stenosis, proptosis, atrial-septal defect, and left inguinal hernia was found, on chromosome analysis, to have a longer than normal terminal band 4p16 by G and R-banding. In situ hybridization of biotin-labeled DNA probes C39, BJ14, BJ54, BJ19, BJ7, and BJ11 showed them to be duplicated. Probes I14, A157.1, and the telomeric sequence, (TTAGGG)n, which hybridized to the more distal part of 4p16.3, were not duplicated. These results confirm the impression by G and R-banding of a duplication within band 4p16, a region extending from approximately 2.1 Mb from the telomere, proximally, to the junction of 4p16.1 and 4p15.3. This is the smallest confirmed duplication of distal 4p reported to date, with many of the classical findings of dup(4p) syndrome.

The Wolf-Hirschhorn syndrome in fetuses

Wolf-Hirschhorn syndrome (WHS) with partial deletion of the short arm of chromosome 4 has been exceptionally diagnosed in fetuses. We report prenatal diagnosis of five cases of monosomy 4p. The fetuses were karyotyped for severe intrauterine growth retardation (IUGR) diagnosed on routine ultrasound (US). In addition, cleft-lip and palate and diaphragmatic hernia respectively were found in two cases. The quantity of amniotic fluid was normal in all cases. At autopsy, the fetuses showed the typical craniofacial dysmorphy but without microcephaly. Major renal hypoplasia was the only constant visceral anomaly. Midline fusion defects were observed in all the fetuses, ranging from minor abnormalities such as scalp defect, hypertelorism, pulmonary isomerism, common mesentery, hypospadias and sacral dimple, to cleft palate, corpus callosum agenesis, ventricular septal defect, and diaphragmatic hernia. On post-mortem X-rays, a delayed bone age was always observed. All the placentae were hypotrophic, and two exhibited vascular lesions, although there was no maternal hypertension. Chromosomal studies showed that the breakpoints were within the 4p16 band in three cases, the 4p15 band in one case, and the 4p14 band in one case. The deletion was de novo in four cases, and resulted from a paternal translocation in one case. This study emphasizes the importance of karyotyping all fetuses with IUGR, especially when the quantity of amniotic fluid is normal, and suggests the possibility of recognizing on US the particular phenotype of WHS in utero.

Molecular detection of a 4p deletion using PCR-based polymorphisms: a technique for the rapid detection of the Wolf-Hirschhorn syndrome

Wolf-Hirschhorn syndrome (WHS) results from a deletion of part of chromosome 4p. The region of 4p consistently deleted in WHS is near the tip of 4p. Two loci in this region D4S95 and D4S125 are associated with highly informative VNTR polymorphisms and were recently converted to allow PCR-based screening. PCR analysis was used successfully to identify a small de novo deletion of 4p in a patient suspected of having WHS. This procedure allows a rapid and accurate confirmation of 4p deletions in cases where cytogenetics alone cannot provide a clear answer.

Clinical, cytogenetic and molecular investigations in three patients with Wolf-Hirschhorn syndrome

Clinical, cytogenetic and molecular studies were performed in three patients with Wolf-Hirschhorn syndrome (WHS). In all cases the altered chromosome 4 appeared to be the result of a de novo deletion. Cytogenetic investigations located the breakpoint at 4p15.3 and 4p13. With cytogenetic methods it was not possible to decide whether these deletions were terminal or interstitial. DNA methods also failed to define a distal breakpoint within the 4p16.3 region which might have indicated an interstitial deletion. According to the literature, the paternal chromosome 4 is preferentially deleted in most patients with WHS. DNA analysis with polymorphic markers out of the 4p16.3 region revealed that in two of the cases reported here the deleted segment was of paternal and in one case of maternal origin.

A complex rearrangement associated with sex reversal and the Wolf-Hirschhorn syndrome: a cytogenetic and molecular study

We report a male infant referred with multiple congenital abnormalities consistent with the Wolf-Hirschhorn syndrome. Cytogenetic analysis showed a chromosome complement of 46,XX with a deletion of 4p15.2----4pter and its replacement by material of unknown origin. The patient was positive for a number of Yp probes including SRY, the testis determining factor, and in situ hybridisation localised the Yp material to the tip of the short arm of one X chromosome. Using pDP230, a probe for the pseudoautosomal region, and M27 beta, which recognises a locus in proximal Xp, the material translocated on to 4p was identified as originating from the short arm of the paternal X chromosome. The most reasonable explanation for this complex rearrangement is two separate exchange events involving both chromatids of Xp during paternal meiosis. An aberrant X-Y interchange gave rise to the sex reversal and an X;4 translocation resulted in additional, apparently active Xp material and a deletion of 4p which produced the Wolf-Hirschhorn phenotype.

Paternal origin of the de novo deleted chromosome 4 in Wolf-Hirschhorn syndrome

The parental origin of the de novo deleted chromosome 4 was studied in five cases of Wolf-Hirschhorn syndrome using polymorphic probes mapping in the 4p16.3 region. In all the patients the deleted chromosome was found to be of paternal origin and these results, together with similar ones obtained by another group, make the preferential paternal origin of the de novo chromosome 4 deletion highly significant.