Two rare cases of 6p partial deletion

Partial deletion of chromosome 6p causing developmental delay and mild dysmorphisms in a child: molecular and developmental investigation and literature search

Background

The interstitial 6p22.3 deletions concern rare chromosomal events affecting numerous aspects of both physical and mental development. The syndrome is characterized by partial deletion of chromosome 6, which may arise in a number of ways.

Case presentation

We report a 2.8-year old boy presenting with developmental delay and mild dysmorphisms. High-resolution oligonucleotide microarray analysis revealed with high precision a 2.5 Mb interstitial 6p deletion in the 6p22.3 region which encompasses 13 genes.

Conclusions

Identification and in-depth analysis of cases presenting with mild features of the syndrome will sharpen our understanding of the genetic spectrum of the 6p22.3 deletion.

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.

Schizophrenia in an adult with 6p25 deletion syndrome

Chromosomal deletions at 6p25-p24 are rare findings in patients with developmental delay. There is limited information about the adult phenotype. We present a 36-year-old patient with schizophrenia, mild mental retardation, progressive hearing deficits, and characteristic facial features. Ocular (Axenfeld-Rieger anomaly) abnormalities were diagnosed in infancy; vision, however, has remained unimpaired. There were no other major congenital anomalies. Brain imaging showed only minor changes. There was no family history of intellectual deficits or psychosis. Karyotyping revealed a 6p25 deletion, and detailed fluorescence in situ hybridization (FISH) analyses using 23 probes confirmed a 6.7 Mb 6p25-pter deletion. The breakpoint is near a possible 6p25-p24 locus for schizophrenia. Psychotic illness may be part of the neurodevelopmental abnormalities and long-term outcome of patients with 6p terminal deletions. Other similarly affected patients likely remain to be diagnosed in adult populations of schizophrenia and/or mental retardation.

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.

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.

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.

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.

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.

Chromosome 3p23 break with ring formation and translocation of displaced 3p23-->pter segment to 6pter

An 11 year old boy with short stature, learning difficulties, and no obvious facial anomalies has a ring (3)(p23q29) formed by a break in the short arm at 3p23 and subsequent fusion with 3qter. A second rearrangement involving translocation of the displaced 3p23-->pter segment to chromosome 6 at 6pter is non-reciprocal with no obvious loss of distal 6pter material. The involvement of one chromosome in two separate rearrangements is uncommon. The patient's relatively mild phenotype appears to be associated with the "ring syndrome" and ring instability in division rather than from any segmental aneuploidy resulting from the presence of the two rearrangements.

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.

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.

Partial deletion of chromosome 6p: delineation of the syndrome

Here we summarize the clinical findings of five new patients and nine patients reported in the literature with deletions of the short arm of chromosome 6. The del(6p) syndrome appears to include the following clinical findings: mental retardation, microcephaly, abnormal sutures, broad nasal bridge, various eye and ear abnormalities, a short neck with excess skin folds, and a normal birth weight and length.