Terminal deletion 6p23: a case report

Assessment of candidate genes and genetic heterogeneity in human non syndromic orofacial clefts specifically non syndromic cleft lip with or without palate

Non syndromic orofacial clefts specifically non-syndromic cleft lip/palate are one of the most common craniofacial malformation among birth defects in human having multifactorial etiology with an incidence of 1:700/1000. On the basis of association with other congenital malformations or their presence as isolated anomaly, OFC can be classified as syndromic (30%) and nonsyndromic (70%) respectively. The major cause of disease demonstrates complex interplay between genetic and environmental factors. The pathogenic mechanism of underlying factors have been provided by different genetic studies on large-scale with significant recent advances in genotyping technologies usually based on linkage or genome wide association studies (GWAS). On the basis of recent studies, new tools to identify causative genes involved in NSCL/P reported approximately more than 30 genetic risk loci that are responsible for pathogenesis of facial deformation. Despite these findings, it is still uncertain that how much of variance in NSCL/P predisposing factors can be explain by identified risk loci, as they all together accounts for only 20%-25% of NSCL/P heritability. So there is need of further findings about the problem of rare low frequency coding variants and other missing responsive factors or genetic modifiers. This review will described those potential genes and loci reported in different studies whose involvement in pathogenesis of nonsyndromic OFC has wide scientific evidence.

6p25 interstitial deletion in two dizygotic twins with gyral pattern anomaly and speech and language disorder

Submicroscopic 6p25 deletion is now recognized as a clinically identifiable syndrome, characterized by intellectual disability, language impairment, hearing deficit, craniofacial, ophthalmologic, cardiac, and varying central nervous system anomalies. We report on two dyzogotic twins with a maternal segregating hemizygous interstitial deletion on chromosome 6p25.1, spanning 0.9 kb; the smallest ever reported. Both had dysmorphic features (prominence of the metopic suture, synophrys, hypertelorism, down-slanting palpebral fissures, tented mouth), and a distinct brain MRI, showing a focal significant increase of the right peri-frontal subarachnoid space, with shallow sulci and a mild anomaly of the gyral pattern. Such brain anomaly has never been reported in association with del 6p25. Both propositi had a borderline-mild intellectual disability, speech and language difficulties, and behavior abnormalities. Their mother, formally tested, had a borderline cognitive impairment. Although none of the genes mapping to the deleted region are apparently related to the phenotype, LYRM4 resulted down-regulated in the cerebellar cortex of schizophrenia patients compared with controls, and Lyrm4 was down-regulated in the prefrontal cortex of mice with microdeletions in the locus syntenic to human 22q11.2 patients affected by schizophrenia. These data are in agreement with the emerging concept that similar CNVs are pathogenic in patients affected by distinct neurological diseases, and that these loci are more general risk factors for different disorders. The resemblance of our patients to those with the more extensive 6p25.1p25.3 terminal deletion suggests that the gene/s responsible for the physical phenotype should reside in the 6p25.1 genomic region.

Chromosome 6p25 deletion syndrome: report of a case with optic disc coloboma and review of published ophthalmic findings

PURPOSE

The 6p25 deletion syndrome is a rare disorder characterized by Dandy-Walker malformation, congenital heart defects, developmental delay, dysmorphic facial features, and malformations of the anterior segment of the eye with a risk for glaucoma. Here we report a child harboring a cryptic de novo 6p25 deletion, bilateral optic disc coloboma and characteristic anterior segment anomalies. We review reported ophthalmic findings in patients with this syndrome.

MATERIALS AND METHODS

Retrospective case review of a 4-day-old male with Dandy-Walker malformation and cardiac defects who was referred with a suspected diagnosis of iris coloboma.

RESULTS

The ophthalmic examination showed bilateral corectopia associated with posterior embryotoxon. Fundus examination revealed bilateral optic disc excavation, which was diagnosed as colobomatous because of its configuration and stability over time. Because of the association of posterior embryotoxon with Dandy-Walker malformation, a terminal 6p deletion syndrome was clinically suspected. Array comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH) studies revealed a 3.2 Mb deletion at 6p25.2p25.3 including the FOXC1 gene. Neither unaffected parent carried this deletion.

CONCLUSIONS

Optic disc colobomas may be found in patients carrying a 6p25 deletion. This has the potential to confound assessment of affected children for glaucoma and intracranial hypertension.

Deletions in chromosome 6p22.3-p24.3, including ATXN1, are associated with developmental delay and autism spectrum disorders

Interstitial deletions of the short arm of chromosome 6 are rare and have been associated with developmental delay, hypotonia, congenital anomalies, and dysmorphic features. We used array comparative genomic hybridization in a South Carolina Autism Project (SCAP) cohort of 97 subjects with autism spectrum disorders (ASDs) and identified an ~ 5.4 Mb deletion on chromosome 6p22.3-p23 in a 15-year-old patient with intellectual disability and ASDs. Subsequent database queries revealed five additional individuals with overlapping submicroscopic deletions and presenting with developmental and speech delay, seizures, behavioral abnormalities, heart defects, and dysmorphic features. The deletion found in the SCAP patient harbors ATXN1, DTNBP1, JARID2, and NHLRC1 that we propose may be responsible for ASDs and developmental delay.

Human genetic factors in nonsyndromic cleft lip and palate: an update

Nonsyndromic cleft lip and/or palate (or orofacial cleft, OFC) is a malformation characterized by an incomplete separation between nasal and oral cavities without any associated anomalies. The last point defines the distinction between syndromic and nonsyndromic OFC. Nonsyndromic OFC is one of the most common malformations among live births and is composed of two separate entities: cleft lip with or without cleft palate (CL+/-P) and cleft palate isolated (CPI). Because of the complex etiology of nonsyndromic OFC, which is due to the differences between CL+/-P and CPI, and the heterogeneity of each group, caused by the number of genes involved, the type of inheritance, and the interaction with environmental factors, we reviewed those genes and available loci in the literature whose involvement in the onset of nonsyndromic OFC has more sound scientific evidence. Genetic studies on human populations have demonstrated that CL+/-P and CPI have distinct genetic backgrounds and, therefore, environmental factors probably disclose only these malformations. In CL+/-P several loci, OFC from 1 to 10 have been identified. The first locus, OFC1, has been mapped to chromosome 6p24. Other CL+/-P loci have been mapped to 2p13 (OFC2), 19q13.2 (OFC3) and 4q (OFC4). OFC5-8 are identified by mutations in the MSX1, IRF6, PVRL1, and TP73L gene, respectively. OFC9 maps to 13q33.1-q34, whereas OFC10 is associated with haploinsufficiency of the SUMO1 gene. In addition, MTHFR, TGF-beta3, and RARalpha play a role in cleft onset. In CPI one gene has been identified (TBX22) at present, but others are probably involved. Greater efforts are necessary in order to have a complete picture of the main factors involved in lip and palate formation. These elements will permit us to better understand and better treat patients affected by OFC.

Case of chromosome 6p25 terminal deletion associated with Axenfeld-Rieger syndrome and persistent hyperplastic primary vitreous

Axenfeld-Rieger syndrome is inherited in an autosomal dominant pattern and is characterized by anomalies of the anterior segment of the eye and systemic signs including craniofacial dysmorphic features and cardiac defects. The disorder is genetically heterogeneous and one causative gene, FOXC1, is located on chromosome 6p25. Persistent hyperplastic primary vitreous (PHPV) is a congenital ocular disorder in which there is a failure of the normal regression of the primary vitreous and a proliferation of fibrous tissue from the remnants of the primary vitreous. Deletions of chromosome 6p25 have been reported in a small number of patients with Axenfeld-Rieger syndrome; however, no case of chromosome 6p25 deletion has been reported with PHPV. We report a newborn girl who had both Axenfeld-Rieger syndrome and the combined type of PHPV, in whom the G-banding and spectral karyotyping revealed a 6p monosomy of terminal deletion with a breakpoint at chromosome 6p25.1. The karyotype was 46,XX,del(6)(p25.1). We conclude that PHPV in the context of Axenfeld-Rieger syndrome can be caused by 6p25 terminal deletion.

Mild developmental delay in terminal chromosome 6p deletion

Deletions involving the short arm of chromosome 6 are relatively rare. Although features of this condition are variable, common findings include developmental delay, ocular abnormalities, hearing loss, and cardiac defects. In an effort to define further the clinical variability of this condition, we report a 6-year-old female with a de novo terminal deletion of chromosome 6 at band 6p24, with mild gross motor delays and normal cognition.

Phenotypic and molecular assessment of seven patients with 6p25 deletion syndrome: relevance to ocular dysgenesis and hearing impairment

Background

Thirty-nine patients have been described with deletions involving chromosome 6p25. However, relatively few of these deletions have had molecular characterization. Common phenotypes of 6p25 deletion syndrome patients include hydrocephalus, hearing loss, and ocular, craniofacial, skeletal, cardiac, and renal malformations. Molecular characterization of deletions can identify genes that are responsible for these phenotypes.

Methods

We report the clinical phenotype of seven patients with terminal deletions of chromosome 6p25 and compare them to previously reported patients. Molecular characterization of the deletions was performed using polymorphic marker analysis to determine the extents of the deletions in these seven 6p25 deletion syndrome patients.

Results

Our results, and previous data, show that ocular dysgenesis and hearing impairment are the two most highly penetrant phenotypes of the 6p25 deletion syndrome. While deletion of the forkhead box C1 gene (FOXC1) probably underlies the ocular dysgenesis, no gene in this region is known to be involved in hearing impairment.

Conclusions

Ocular dysgenesis and hearing impairment are the two most common phenotypes of 6p25 deletion syndrome. We conclude that a locus for dominant hearing loss is present at 6p25 and that this locus is restricted to a region distal to D6S1617. Molecular characterization of more 6p25 deletion patients will aid in refinement of this locus and the identification of a gene involved in dominant hearing loss.

Bilateral dentigerous cyst associated with polymorphism in chromosome 1qh+

Non-syndromal bilateral dentigerous cysts are rare. It is conceivable that they are either under-recognized or under-reported. In this article we report the unusual occurrence of non-syndromic bilateral dentigerous cysts associated with mandibular third molars with polymorphism in chromosome 1qh+. It is suggested that in non syndromal cases of bilateral dentigerous cysts karyotyping should be done to confirm the association with chromosomal 1 anomaly.

Prenatal diagnosis of deletion of chromosome 6p presenting with hydrops fetalis

OBJECTIVE

To report the first known case of 6p deletion presenting in utero with hydrops fetalis and multiple anomalies in the second trimester of pregnancy.

METHODS

A thirty-year-old woman (gravida 3 para 1 abortion 1) was referred to our hospital at 18 weeks of gestation because of suspicion of fetal anomaly on routine ultrasound examination. A detailed anomaly scan revealed a single viable fetus with marked skin edema, marked ascites, pleural effusion, hydronephrosis of left kidney, absence of right kidney, cardiac anomaly and oligohydramnios. The fetal face was not visible due to the fetal position. Fetal karyotyping revealed 46,XX,del(6)(p21.3). The couple opted to terminate the pregnancy.

RESULTS

A hydropic female fetus was aborted and the autopsy revealed hydrops fetalis with bilateral cleft lips, hydronephrosis of left kidney, absence of right kidney, spleen, and thymus gland, truncus arteriosus, and single umbilical artery. Cord blood and tissue culture confirmed that the fetus had deletion of chromosome 6p.

CONCLUSION

Deletion of short arm of chromosome 6 can result in hydrops fetalis in early pregnancy.

Genetics of cleft lip and palate revisited

Cleft lip with or without cleft palate (CL/CP) is one of the most common structural birth defects with treatment including multiple surgeries speech therapy, and dental and orthodontic treatments over the first 18 years of life. Providing care for these patients and families includes educating patients and parents about the genetics of CL/CP, as well as meeting the immediate medical needs. Attempts at identifying susceptibility loci via family and case-control studies have proved inconsistent. It is likely that initial predictions of the complex interactions involved in facial development were underestimated. The candidate gene list for CL/P is getting longer and the need for an impartial systematic screening technique, to implicate or refute the inclusion of particular loci, is apparent. So we are faced with the question "Can this complex trait be too complex?" The aim of this review is to make the dentist aware of the differences between syndromic and non-syndromic cleft as well as understanding the etiological variation in cleft lip with and without cleft palate. This will aid the dentist in diagnosis and give proper genetic counseling to parents and patients of cleft lip and palate.

Severe musculoskeletal phenotype associated with an unbalanced t(6;10) translocation: clarification of the locus for this phenotype on distal 6p

Larsen syndrome is a congenital condition consisting of multiple large joint dislocations associated with a distinctive facial appearance and frequently other abnormalities. The syndrome is probably genetically heterogeneous, with both dominant and recessive inheritance reported. Previously two cases have been reported where a Larsen-like syndrome was associated with unbalanced chromosomal translocations resulting in partial trisomy 1q and monosomy distal 6p. We now report a child with an unbalanced translocation resulting in a distal 6p deletion and partial trisomy 10q, who has Larsen-like features and has also severe developmental delay. A G-banded preparation revealed a karyotype 46,XX,der(6),t(6:10)(p25;q25.2) and the breakpoint at 6p25 was confirmed by FISH using YAC probes (between 6p25 at D6s477/F13A1 and 6p24 at 6WI13606). Our case provides further evidence for a Larsen-like locus at distal 6p and reduces the potential critical region.

Recent developments in orofacial cleft genetics

Nonsyndromic cleft of the lip and/or palate (CLP or orofacial cleft) derives from an embryopathy with consequent failure of the nasal process and/or palatal shelves fusion. This severe birth defect is one of the most common malformations among live births. Nonsyndromic CLP is composed of two separate entities: cleft lip and palate (CL+/-P) and cleft palate only (CPO). Both have a genetic background, and environmental factors probably disclose these malformations. In CL+/-P, several loci have been identified, and, in one case, a specific gene has also been found. In CPO, one gene has been identified, but many more are probably involved. Because of the complexity of the genetics of nonsyndromic CLP as a result of the difference between CL+/-P and CPO, heterogeneity of each group caused by the number of involved genes, type of inheritance, and interaction with environmental factors, we discuss the more sound results obtained with different approaches: epidemiological studies, animal models, human genetic studies, and in vitro studies.

The 6p deletion syndrome: a new orofacial clefting syndrome and its implications for antenatal screening

Foetal genetic screening has become the centre of the ethical debate surrounding the screening of foetuses for chromosomal defects to help create 'eugenic' children with either perceived advantageous characteristics or traits that could be used to medically aid unhealthy siblings. This report highlights the problems facing the medical establishment by citing, by way of example, a case of a genetic abnormality producing a clefting syndrome. The 6p deletion syndrome was first described almost 20 years ago, and the evidence is mounting for its inclusion as an orofacial clefting syndrome. This case report includes a description of the syndrome, the method used for detecting chromosomal aberrations and a comparison with other reports of the syndrome published to date. However, by pursuing a genetic-testing policy at our unit to detect new abnormalities or to help substantiate previously reported abnormalities, the way could be left open for its subsequent abuse by parents and corporations alike, so having implications not only for the individual but also for the unit performing the test. A brief synopsis is therefore also provided regarding the current circumstances of foetal screening in the UK.

Axenfeld-Rieger anomaly, hypertelorism, clinodactyly, and cardiac anomalies in sibs with an unbalanced translocation der(6)t(6;8)

We describe two sibs with the unbalanced translocation der(6)t(6;8)(p25.1;q24.23), making them monosomic for 6p25.1-->6pter and trisomic for 8q24.23-->8qter. The siblings both possess Axenfeld-Rieger Anomaly (ARA), hypertelorism, clinodactyly, and cardiac anomalies, but otherwise vary in the phenotypic manifestations of this unbalanced translocation. We compare them to previously described cases and a recently proposed syndrome of ARA, atrial septal defect, and sensorineural deafness.

Genetics of nonsyndromic cleft lip and palate: a review of international studies and data regarding the Italian population

The aims of this review are (1) to illustrate current knowledge of the mode of inheritance and the loci involved in the cleft lip and palate and (2) to summarize the results of our investigations, which were carried out in Italy. It is well established that nonsyndromic cleft of the lip with or without the palate (CL+/-P) and cleft palate only (CPO) are separate entities. Genetic heterogeneity has been observed in CL+/-P, which involves different chromosome regions, mainly 6p23 (OFC1), 2q13 (OFC2), and 19q13.2 (OFC3), as well as other loci, such as 4q25-4q31.3 and 17q21. Furthermore, an interaction between different genes has been suggested in the oligogenic model. In one case at least, an OFC1 and OFC2 interaction has been demonstrated. The mode of inheritance of CPO is compatible with a recessive single major gene model, while an association with a candidate gene, mapping on the chromosome region 2q13/TGFalpha, remains to be confirmed.

Distal 6p deletion syndrome: a report of a case with anterior chamber eye anomaly and review of published reports

We describe a 32 year old male with a distal 6p24.3-->pter deletion. He has specific developmental anomalies of the anterior chamber of the eye and a cleft uvula which is consistent with the recent localisation of genes for iris development and orofacial clefting to distal 6p. In addition he has progressive sensorineural deafness and this may localise a gene for deafness to this region. We conclude that a refined distal 6p deletion syndrome exists and includes a characteristic facial appearance with hypertelorism, downward slanting palpebral fissures, tented mouth, smooth philtrum, palatal malformation, ear anomalies, anterior chamber eye defects, progressive sensorineural deafness, cardiac defects, abdominal herniae, small external genitalia, and motor and speech delay.

Suggestive linkage between markers on chromosome 19q13.2 and nonsyndromic orofacial cleft malformation

Nonsyndromic cleft lip with or without cleft palate (OFC) is a common birth defect that has genetic bases. The nature of the genetic contribution is still to be clarified; however, some chromosome regions and candidate genes have been proposed for this malformation. We examined linkage between BCL3, a proto-oncogene located in 19q13.2, and OFC in a sample composed of 40 multiplex pedigrees using both nonparametric and parametric methods. The affected pedigree member statistics and the transmission disequilibrium test supported a role for BCL3 in causing OFC, while no evidence of linkage or genetic heterogeneity was found with the lod score method.

Ocular abnormalities in a patient with partial deletion of chromosome 6p. A case report

We report on a patient with a de-novo deletion of chromosome 6p. This male infant presented with multiple systemic congenital defects together with an unusual ocular phenotype. Slit-lamp examination revealed thin, opaque, rectilinear bands within the anterior segment partially connecting iris to corneal endothelium. These were associated with bilateral hyperopia and optic nerve hypoplasia. Ocular abnormalities in such patients have been documented although the number of individuals is small and identical cytogenetic defects are rarely encountered. We compare the clinical findings in this case with previously described phenotypes. Characterisation of such cases is important as it is becoming apparent that deletion of genetic information encoded on chromosome 6p has implications for ocular embryogenesis.

Evidence of linkage to 6p23 and genetic heterogeneity in nonsyndromic cleft lip with or without cleft palate

Nonsyndromic cleft lip with or without cleft palate (CL+/-P) is a congenital orofacial anomaly that derives from an embryopathy with failure of nasal process and palatal shelves fusion. CL+/-P is one of the most common malformations, affecting 1/700-1/1000 live births among Caucasians. Early investigations have suggested that a clefting gene may be located on the short arm of chromosome 6 (6p), as well as in other regions. In this study, we analyzed a large sample of families by using eight PCR markers that map on chromosome region 6p23-p24. The admixture test, as implemented in the HOMOG program, was significant when tested against multipoint data (alpha = 0.60, P value 0.00004); the lod score calculated, assuming heterogeneity, was 3.60 at 1 cM telomeric to D6S259. Taken together these data demonstrate the presence of a locus for CL+/-P in the 6p23 chromosome region.

Partial deletion of chromosome 6p: autopsy findings in a premature infant and review of the literature

Autopsy findings for a premature infant with terminal deletion of 6p [46, XY, del(6)p23] are reported. The infant had multiple dysmorphic features, cleft lip and palate, abnormal external genitalia, diverticulum of right ventricle, and hydrocephalus with cerebellar hypoplasia, with absent corpus callosum and cerebellar vermis.

A new form of long QT syndrome associated with syndactyly

OBJECTIVES

The purpose of this study was to characterize a possible association between long QT syndrome and syndactyly.

BACKGROUND

Long QT syndrome causes syncope and sudden death from ventricular arrhythmias. Syndactyly is a developmental disorder that causes webbing of the hands and feet. Both disorders can be inherited as isolated, autosomal dominant traits, but an association between them has not been established.

METHODS

We identified three children with long QT syndrome, atrioventricular (AV) block and simple syndactyly. Phenotypic and laboratory data were obtained from families, attending physicians and medical records.

RESULTS

All patients had bilateral cutaneous syndactyly and were diagnosed with long QT syndrome within the 1st 2 years of life. Structural heart disease, particularly a patent ductus arteriosus, was present in all three patients. Analysis of electrocardiograms showed marked prolongation of the QT intervals with rate-corrected QT intervals of 633, 628 and 680 ms, respectively. Transient AV block was also noted. Two of the three children died suddenly despite treatment with beta-adrenergic blocking agents and permanent pacing.

CONCLUSIONS

We postulate that these children have a new form of long QT syndrome associated with syndactyly and a high risk of sudden death. The association of syndactyly with long QT syndrome may provide insight into the mechanisms underlying both disorders. Patients with syndactyly should be evaluated for the presence of long QT syndrome, and if it is found, aggressive treatment may be warranted.

Multiple congenital anomalies in a man with (X;6) translocation

X;autosome translocations in humans, often associated with congenital anomalies or with gonadal dysgenesis syndromes, are informative for the study of X-linked gene expression and of the phenomenon of X chromosome inactivation. When such translocations occur in association with multiple congenital anomaly (MCA) syndromes, the observed phenotypes are not always attributable solely to disruption of specific genes, if X-inactivation spreads onto the translocated autosome, rendering some distal genes inactive. We report on a man with multiple congenital anomalies and a maternally inherited (X;6)(p22.1;p25) translocation. He has abnormalities not described in the Klinefelter or 6p deletion syndromes. His unique findings constitute a recognizable syndrome, which is likely caused by disomy for a region of Xp in conjunction with a partial 6p deletion.

Exclusion of candidate genes from a role in cleft lip with or without cleft palate: linkage and association studies

Candidate genes and marker loci for cleft lip/palate (CL/P) were tested using linkage analyses and association studies. Eight British families with apparent autosomal dominant inheritance of non-syndromic CL/P participated in the linkage analyses while the association analyses involved 61 unrelated British white people with CL/P and 60 controls. The report of an association between RARA (17q21) and unrelated Australian persons with CL/P (p = 0.016) was not confirmed in British CL/P persons (chi 2 = 0.954, p > 0.1). There was also no evidence of linkage between RARA and the eight CL/P families (Z = -3.211, theta = 0.001). Linkage was excluded between familial CL/P and F13A1 (map position 6p24-25) with an observed maximum lod score of Z = -2.052 at theta = 0.05. No association was found between alleles at VIM (10p13) and the British CL/P subjects (chi 2 = 0.110, p > 0.5). Multipoint analysis excluded linkage between familial CL/P and the markers D1S65 and D1S58 which flank the Van der Woude syndrome locus with a maximum lod score of Z = -4.0. This suggests that the genetic defect underlying VWS is not the same as in non-syndromic CL/P. There was no evidence of linkage between CRTL1 (5q15) and the eight CL/P families (Z = -3.466, theta = 0.05).

Mapping of RXRB to human chromosome 6p21.3

Retinoid X Receptor beta (RXRB) is a member of the retinoid X receptor (RXR) family of nuclear receptors which are involved in mediating the effects of retinoic acid (RA). We have confirmed the localization of RXRB to chromosome 6 and we have mapped the gene to chromosome 6p21.3-p21.1 by PCR amplification of 5' untranslated sequence in panels of rodent-human somatic cell hybrids and to 6p21.3 by fluorescent in situ hybridization.

6p23 deletion mosaicism in a woman with recurrent abortions and idiopathic hypoprolactinemia

A woman with a history of recurrent abortions, idiopathic hypoprolactinemia, and an apparent 6p partial deletion mosaicism is described. The breakpoint in the short arm of chromosome 6 was in the p23 region. This deletion could have been caused by a fragile site in 6p23.