Ring chromosome 14: a distinct clinical entity

Guideline recommendations for diagnosis and clinical management of Ring14 syndrome-first report of an ad hoc task force

Background

Ring chromosome 14 syndrome is a rare chromosomal disorder characterized by early onset refractory epilepsy, intellectual disability, autism spectrum disorder and a number of diverse health issues.

Results

The aim of this work is to provide recommendations for the diagnosis and management of persons affected by ring chromosome 14 syndrome based on evidence from literature and experience of health professionals from different medical backgrounds who have followed for several years subjects affected by ring chromosome 14 syndrome. The literature search was performed in 2016. Original papers, meta-analyses, reviews, books and guidelines were reviewed and final recommendations were reached by consensus.

Conclusion

Conventional cytogenetics is the primary tool to identify a ring chromosome. Children with a terminal deletion of chromosome 14q ascertained by molecular karyotyping (CGH/SNP array) should be tested secondarily by conventional cytogenetics for the presence of a ring chromosome. Early diagnosis should be pursued in order to provide medical and social assistance by a multidisciplinary team. Clinical investigations, including neurophysiology for epilepsy, should be performed at the diagnosis and within the follow-up. Following the diagnosis, patients and relatives/caregivers should receive regular care for health and social issues. Epilepsy should be treated from the onset with anticonvulsive therapy. Likewise, feeding difficulties should be treated according to need. Nutritional assessment is recommended for all patients and nutritional support for malnourishment can include gastrostomy feeding in selected cases. Presence of autistic traits should be carefully evaluated. Many patients with ring chromosome 14 syndrome are nonverbal and thus maintaining their ability to communicate is always essential; every effort should be made to preserve their autonomy.

Epilepsy in ring 14 chromosome syndrome

Ring chromosome 14 [r(14)] is a rare disorder. The aim of this study was to describe two new cases of r(14) drug-resistant epilepsy, and, through an extensive review of literature, highlight those epileptological features which are more commonly found and which may help in early diagnosis, genetic counseling, and treatment. Epilepsy onset in r(14) syndrome takes place during the first year of life; seizures are generalized or focal and less frequently myoclonic. Seizures might be induced by fever. Focal seizures are characterized by staring, eye or head deviation, respiratory arrest, swallowing, and hypertonia/hypotonia or clonic movements. Ictal EEG might show both focal and diffuse discharges. Interictal EEG reveals mainly focal abnormalities. Mental retardation represents a constant feature. Neurological assessment yields a delay in motor skill acquisition and less frequently both pyramidal and cerebellar signs. Dysmorphic features are evident in the majority of cases. Epilepsy associated with r(14) has many features that entail a challenging diagnostic process. The reported cases of r(14)-related epilepsy seem to highlight a series of common elements which may be helpful in pointing the clinician towards a correct diagnosis.

Ring chromosome 20 syndrome: electroclinical description of six patients and review of the literature

BACKGROUND

Ring chromosome 20 syndrome is a rare chromosomal disorder.

METHODS

In six patients, we focused on the presenting epileptic phenotype, the behavioral and mental problems and the relationship between the ratio of mosaicism and the age at onset of the epilepsy.

RESULTS

All patients presented with pharmacoresistant frontal lobe complex partial seizures. The earliest onset of epilepsy was seen in patients without mosaicism. There were three patients out of six with behavioral disturbances before the onset of seizures. All patients had mild to moderate cognitive impairment. Electroencephalogram recordings showed rhythmic theta waves with frontal predominance and non-convulsive status epilepticus (NCSE).

CONCLUSIONS

The ring chromosome 20 syndrome is characterized by childhood-onset refractory epilepsy continuing throughout adult life, mental disability, and behavioral disturbances which can originate before seizure onset. Ictal EEG reveals a unique pattern. Our findings indicate a possible link between the percentage of affected cells and the age of epilepsy onset.

Genetics of epilepsy: an overview

Studies of the genetics of epilepsy have, until recently, involved epidemiologic or segregation analyses of phenotypic characteristics of a number of seizure disorders. Technical advances in molecular biology involving gene mapping and gene identification have made it possible to examine the heritability of various epilepsy syndromes. Using "reverse genetics" or positional cloning, it is possible to identify an abnormal protein through gene isolation and cloning. Genes are localized through analysis of linkage to phenotypic markers (proteins) or DNA markers such as restriction fragment length polymorphisms, variable number of tandem repeats, and dinucleotides. Methods used to obtain DNA of interest involve digestion of genomic DNA with specific restriction endonucleases or amplification of DNA by polymerase chain reaction technology. Gel electrophoresis is the basis for the separation of different sized DNA. Inherited disorders for which a gene has been cloned or localized have highly penetrant, well-defined clinical phenotypes with no remissions and abundant clinical material. Genetic epilepsies, however, are variably penetrant age-dependent disorders with heterogeneous clinical phenotypes. Despite these difficulties, three genetic epilepsies have been mapped to specific chromosomes: benign familial neonatal convulsions to 20q, juvenile myoclonic epilepsy to 6p, and Baltic progressive myoclonus epilepsy to 21q. Further progress in understanding genetic epilepsies will depend on better definition of syndrome phenotypes, isolation of the epilepsy gene(s), and identification of the abnormal protein(s).

Ring 14 chromosome presenting as early-onset isolated partial epilepsy

We report four infants (two males, two females) with ring 14 chromosome presenting with early-onset partial epilepsy. The first seizure occurred between 3 and 6 months (3, 3, 4, and 6mo respectively). In all four cases, diagnosis was based on early focal seizures, rather than on psychomotor retardation or morphological features, which were not prominent at seizure onset. Moreover, despite the young age of the patients and the high frequency of seizures, neither epileptic spasms nor progression to 'epileptic encephalopathy', such as hypsarrhythmia, were observed. Epilepsy remained partial in these patients. At the most recent follow-up, all four children had slight or mild psychomotor delay, and two of them had moderate non-specific dysmorphic traits. Data from the literature about epilepsy in ring 14 chromosome syndrome were also reviewed. Ring 14 chromosome syndrome may be revealed by isolated, early-onset focal epilepsy suggestive of focal lesions with only mild mental retardation and morphological features at the time of diagnosis. The characteristics of these observations differ from classic ring 14 syndrome, and may enlarge this clinical spectrum. Many unanswered questions remain concerning phenotype-genotype correlation and identification of the potential genes and molecular mechanisms responsible for epilepsy in patients with ring 14 syndrome.

Mosaic trisomy r(14) associated with epilepsy and mental retardation

We report a patient with moderate mental retardation, benign clinical course of epilepsy, and type 2 diabetes mellitus. The patient has a mosaic karyotype with 2 cell lines: 1 with a ring chromosome 14 [r(14)], and 1 with an apparently duplicated r(14) chromosome.

Ring chromosome formation as a novel escape mechanism in patients with inverted duplication and terminal deletion

Ring chromosomes are rare cytogenetic findings and are associated at phenotypic level with mental retardation and congenital abnormalities. Features specific for ring chromosome syndromes often overlap with the features of terminal deletions for the corresponding chromosomes. Here, we report a case of a ring chromosome 14 which was identified by conventional cytogenetics and shown to have a terminal deletion and an additional inverted duplication with a triplication by using large insert clone and oligo array-comparative genomic hybridization (array-CGH), fluorescence in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA). The combination of an inverted duplication with a terminal deletion in a ring chromosome is of special interest for the described syndromes of chromosome 14. The presented findings might explain partly overlapping clinical features described in terminal deletion, duplication and ring chromosome 14 cases, as these rearrangements can be easily overlooked when performing GTG-banding only. Furthermore, we suggest that ring chromosome formation can act as an alternative chromosome rescue next to telomere healing and capture, particularly for acrocentric chromosomes. To our knowledge, this is the first time an inverted duplication with a terminal deletion in a ring chromosome is identified and characterized using high-resolution molecular karyotyping. Systematic evaluation of ring chromosomes by array-CGH might be especially useful in distinguishing cases with a duplication/deletion from those with a deletion only.

L'épilepsie dans les aberrations chromosomiques

Epilepsy is among the most frequent finding in many chromosome aberrations. While most chromosome aberrations can be associated with different seizure types, there are few aberrations which feature specific seizures and EEG patterns. Among the 400 different chromosomal imbalances described with seizures and EEG abnormalities, eight have a high association with epilepsy. These comprise: the monosomy 1p36, Wolf-Hirschhorn syndrome (4p-), Angelman syndrome, Miller-Dieker del 17p13.3, the inversion duplication 15 syndrome, ring 20 and ring 14 syndromes, Down's syndrome. These chromosomal regions where aberrations have an evident association with epilepsy may be useful targets for gene hunters. On the other hand, a better characterisation of epileptic syndrome in these disorders may lead to a better and specific treatment.

Abnormal pigmentation in hypomelanosis of Ito and pigmentary mosaicism: the role of pigmentary genes

There is increasing evidence that hypomelanosis of Ito and related disorders such as linear and whorled naevoid hypermelanosis are due to mosaicism for a variety of chromosomal abnormalities. This group of disorders is better termed 'pigmentary mosaicism'. In this review we explain how disparate chromosomal abnormalities might manifest as a common pigmentary phenotype. In particular, we provide evidence supporting the hypothesis that the chromosomal abnormalities reported in these disorders specifically disrupt expression or function of pigmentary genes.

Mosaic monosomy 14: clinical features and recognizable facies

A 1-year-old child with clinical features of monosomy 14 is reported. She has dysmorphic facial features including ocular colobomata, dolichocephaly and microcephaly, retinal pigmentation, severe seizures, fair curly hair and tapering fingers. There was severe mental retardation. This is the first reported case of severe mosaic monosomy 14, with up to 30% mosaicism. A recognizable facial gestalt is present in children with 14q deletions or partial monosomy 14, as well as susceptibility to infection, feeding difficulties, seizures and retinal pigmentation.

Ring chromosome 14 with localization-related epilepsy: three cases

Three patients showing epileptic seizures and with mosaicism of ring chromosome 14 and monosomy for chromosome 14 are described. Patients were a 17-year-old boy, karyotype 46, XY, r(14)(p12q32.33)/45, XY, -14, a 7-month-old boy, karyotype 46, XY, r(14)(p11.2q32.33)/45, XY, -14, and a 10-month-old boy, karyotype 46, XY, r(14)(p12q32.31)/45, XY, -14. Microcephaly and alopecia were observed in the first patient. However, few dysmorphic features were found typical of ring 14 chromosome. He had exhibited complex partial seizures with secondary generalization at age 3 months and had mild motor and mental retardation. Both other patients had atonic seizures followed by staring, perioral cyanosis, and respiratory arrest at age 7 or 8 months. Both also showed mild developmental delay and had a few minor anomalies compatible with ring 14 chromosome. Interictal spikes were observed in the second patient in the right occipital region, whereas an interictal encephalogram of the third patient showed sporadic spikes in the left central region. In all three cases, seizures were resistant to common antiepileptic drugs.

Further delineation of the chromosome 14q terminal deletion syndrome

A patient with hypotonia, blepharophimosis, ptosis, a bulbous nose, a long philtrum, upturned corners of the mouth, and mild developmental delay was found to have a small subtelomeric deletion of the long arm of chromosome 14 (q32.31-qter). In comparing her phenotype with previously reported patients with similar 14q deletions, due to either a linear deletion or to a ring chromosome 14, a clinically recognizable terminal 14q microdeletion syndrome was evident. Due to the limited number of cases reported, it was not possible to assign specific features to specific regions of terminal 14q. The comparison of features in cases with a linear deletion of 14qter (n = 19) to those in cases with a deletion due to a ring chromosome 14 (n = 23), both with the same breakpoint in 14q, showed that seizures and retinitis pigmentosa have been found only in patients with ring chromosomes. Several hypotheses are put forward to explain this difference: mitotic instability of ring chromosomes; a telomere position effect in ring chromosomes in which the 14p telomere silences nearby gene(s) on the q-arm; and dose-dependent gene(s) involved in seizures and retinitis pigmentosa located on the short arm of chromosome 14. In our opinion, only seizures may be explained by the mitotic instability of ring chromosomes, while both seizures and retinitis pigmentosa may be explained by silencing of gene(s) on 14q by the 14p telomere; the third hypothesis seems unlikely to explain either symptom.

Chromosomal abnormalities and epilepsy: a review for clinicians and gene hunters

PURPOSE

We analyzed databases on chromosomal anomalies and epilepsy to identify chromosomal regions where abnormalities are associated with clinically recognizable epilepsy syndromes. The expectation was that these regions could then be offered as targets in the search for epilepsy genes.

METHODS

The cytogenetic program of the Oxford Medical Database, and the PubMed database were used to identify chromosomal aberrations associated with seizures and/or EEG abnormalities. The literature on selected small anomalies thus identified was reviewed from a clinical and electroencephalographic viewpoint, to classify the seizures and syndromes according to the current International League Against Epilepsy (ILAE) classification.

RESULTS

There were 400 different chromosomal imbalances described with seizures or EEG abnormalities. Eight chromosomal disorders had a high association with epilepsy. These comprised: the Wolf-Hirschhorn (4p-) syndrome, Miller-Dieker syndrome (del 17p13.3), Angelman syndrome (del 15q11-q13), the inversion duplication 15 syndrome, terminal deletions of chromosome 1q and 1p, and ring chromosomes 14 and 20. Many other segments had a weaker association with seizures. The poor quality of description of the epileptology in many reports thwarted an attempt to make precise karyotype-phenotype correlations.

CONCLUSIONS

We identified certain chromosomal regions where aberrations had an evident association with seizures, and these regions may be useful targets for gene hunters. New correlations with specific epilepsy syndromes were not revealed. Clinicians should continue to search for small chromosomal abnormalities associated with specific epilepsy syndromes that could provide important clues for finding epilepsy genes, and the epileptology should be rigorously characterized.

Current status of human chromosome 14

Over the past three decades, extensive genetic, physical, transcript, and sequence maps have assisted in the mapping of over 30 genetic diseases and in the identification of over 550 genes on human chromosome 14. Additional genetic disorders were assigned to chromosome 14 by studying either constitutional or acquired chromosome aberrations of affected subjects. Studies of benign and malignant tumours by karyotype analyses and by allelotyping with a panel of polymorphic genetic markers have further suggested the presence of several tumour suppressor loci on chromosome 14. The search for disease genes on human chromosome 14 has also been achieved by exploiting the human-mouse comparative maps. Research on uniparental disomy and on the search for imprinted genes has supported evidence of epigenetic inheritance as a result of imprinting on human chromosome 14. This review focuses on the current developments on human chromosome 14 with respect to genetic maps, physical maps, transcript maps, sequence maps, genes, diseases, mouse-human comparative maps, and imprinting.

Ring chromosome 14 complicated with complex partial seizures and hypoplastic corpus callosum

A Japanese male with mosaicism of ring chromosome 14 and chromosome 14 monosomy is described. He demonstrated the characteristic morphologic features of ring chromosome 14, in addition to mental retardation and epileptic seizures. Clusters of complex partial seizures, one of which originated in the left frontocentral region on electroencephalographic monitoring, were evident. His seizures responded to phenobarbital, and his mental and motor development was only mildly retarded. Magnetic resonance imaging revealed a hypoplastic corpus callosum, previously unknown in association with this syndrome.

De novo microdeletion on an inherited Robertsonian translocation chromosome: a cause for dysmorphism in the apparently balanced translocation carrier

Robertsonian translocations are usually ascertained through abnormal children, making proposed phenotypic effects of apparently balanced translocations difficult to study in an unbiased way. From molecular genetic studies, though, some apparently balanced rearrangements are now known to be associated with phenotypic abnormalities resulting from uniparental disomy. Molecular explanations for other cases in which abnormality is seen in a balanced translocation carrier are being sought. In the present paper, an infant is described who has retarded growth, developmental delay, gross muscular hypotonia, slender habitus, frontal bossing, micrognathia, hooked nose, abundant wispy hair, and blue sclerae. Cytogenetically, she appeared to be a carrier of a balanced, paternally derived 14;21 Robertsonian translocation. Analysis of DNA polymorphisms showed that she had no paternal allele at the D14S13 locus (14q32). Study of additional DNA markers within 14q32 revealed that her previously undescribed phenotype results from an interstitial microdeletion within 14q32. Fluorescent in situ hybridization was used to show that this microdeletion had occurred de novo on the Robertsonian translocation chromosome. These observations may reactivate old suspicions of a causal association between Robertsonian translocations and de novo rearrangements in offspring; a systematic search for similar subcytogenetic rearrangements in other families, in which there are phenotypically abnormal children with apparently balanced translocations, may be fruitful. The clinical and molecular genetic data presented also define a new contiguous gene syndrome due to interstitial 14q32 deletion.

Genetic linkage of vitelliform macular degeneration (Best's disease) to chromosome 11q13

Macular degeneration is the most common cause of legal blindness in older patients in developed countries. Best's vitelliform dystrophy is an early-onset, autosomal dominant form of macular degeneration characterized by an egg-yolk-like collection of lipofuscin beneath the pigment epithelium of the retinal macula. Fifty-seven members of a five-generation family affected with this disease were studied. A combination of ophthalmoscopy and electro-oculography was used for diagnosis; 29 patients were found to be affected and 16 unaffected. Linkage analysis mapped the disease-causing gene to chromosome 11q13. Three markers in this region were found to be significantly linked (Zmax > 3.0) to the disease. Multipoint analysis yielded a maximum Lod score of 9.3 in the interval between markers INT2 and D11S871.

Transmission of ring 14 chromosome from mother to two sons

We report on a family with transmission of a ring chromosome 14 from an affected mother to her 2 sons. The mother was mosaic, 46,XX,r(14)/45,XX,t(14q21q). Both of her sons, affected by seizures and mental retardation, have the karyotype 46,XY,r(14). In considering the association of translocation 14:21 in the mother with ring 14, we postulate that either the ring chromosome was formed first and then opened with translocation of the partially deleted chromosome 14 to chromosome 21, or the 14:21 translocation was present first, then the chromosomes 14 and 21 broke apart, and the partially deleted 14 formed the ring. The published literature of cases of ring 14 is reviewed.

Terminal deletion (14)(q32.3): a new case

A mildly dysmorphic, 2 year old girl with mental retardation was found to have a small de novo terminal deletion of the long arm of chromosome 14, del(14)(q32.3). She was found to have features in common with two previous terminal deletion cases and particularly with the well documented ring 14 syndrome, although seizures, a characteristic feature of ring 14, were notably absent.

Unusual cytogenetic mosaicism involving chromosome 14 abnormalities in a child with an MR/MCA syndrome and abnormal pigmentation

An 8-year-old female child with mental retardation (MR), multiple congenital anomalies (MCA) and irregular pigmentation was shown to have karyotypic mosaicism involving chromosome 14 abnormalities. Four cell lines were found in both peripheral blood lymphocytes and skin fibroblasts and were represented by: a normal karyotype, an isopseudodicentric 14q [iso psu dic(14)], a ring 14 [r(14)], and a monosomy 14 [mono(14)]. Our results are compared with reported cases involving multiple abnormalities of specific chromosomes. Karyotypic mosaicism of comparable chromosome 14 abnormalities is rare, with only one known previous case. Detailed analysis of karyotypic mosaicism of rare chromosomal abnormalities is essential to determine meaningful correlations with specific patterns of malformation.

Association of pigmentary anomalies with chromosomal and genetic mosaicism and chimerism

We have evaluated eight patients with pigmentary anomalies reminiscent of incontinentia pigmenti or hypomelanosis of Ito. All demonstrated abnormal lymphocyte karyotypes with chromosomal mosaicism in lymphocytes and/or skin fibroblasts. In seven the skin was darkly pigmented, and in all of these seven cases the abnormal pigmentation followed Blaschko lines. The literature contains at least 36 similar examples of an association between pigmentary anomalies and chromosomal mosaicism, as well as five examples of an association with chimerism. The pigmentary anomalies are pleomorphic, and the chromosomal anomalies involve autosomes and sex chromosomes. The pigmentation patterns are reminiscent of the archetypal paradigm seen in allophenic mice and demonstrate the clonal origin of melanoblasts from neural crest precursors. Patients with anomalous skin pigmentation, particularly when it follows a pattern of Blaschko lines, should be appropriately evaluated for a possible association with chromosomal or genetic mosaicism or chimerism.

[Epilepsy in ring chromosome 14 syndrome]

A patient with ring 14 chromosome is reported. On the basis of this case and of a review of 28 cases published in the literature, the frequency of clinical signs and symptoms is determined, the constant and early incidence of epileptic seizures is emphasized and their characteristics are described. The associated congenital malformations are listed and their importance for karyotyping and consequent detection of new cases is emphasized.

A terminal deletion (14)(q31.1) in a child with microcephaly, narrow palate, gingival hypertrophy, protuberant ears, and mild mental retardation

A female child with a terminal deletion on the long arm of chromosome 14, 46,XX,del(14)(q31.1), presented with microcephaly, narrow palate, gingival hypertrophy, protuberant ears, and a small haemangioma on the back. She was mildly mentally retarded. Only a few patients with a partial deletion of 14q (14q-) have been reported without consistent clinical findings. Although a clinical syndrome associated with ring chromosome 14, r(14), has been established, no distinct pattern has been so far reported in 14q-.

Retinal/macular pigmentation in conjunction with ring 14 chromosome

A number of constant features can be ascribed to patients who have a ring 14 chromosome. Recent publications have described pigmentation of the retinal/macular area of the eye and suggested that it may also be a constant feature of the syndrome. We describe a patient who has a ring 14 with a terminal deletion but no retinal pigmentation and compare our case with other informative cases. We suggest that a region on chromosome 14 proximal to q32.2 may be involved in controlling these changes.

De novo reciprocal translocation t(6;14)(q27;q13.3) in a child with infantile spasms

A boy with infantile spasms was found to have a balanced de novo translocation, 6q;14q. The karyotype was 46,XY,t(6;14)(q27;q13.3). He had mental retardation and microcephaly but no dysmorphic features. Whether or not there is a relationship between the translocation in our patient and his infantile spasms is unknown. If there is a connection, a gene or genes on chromosome 14 may be implicated in the seizure disorders that are common in patients with ring chromosome 14 syndrome or proximal partial trisomy 14 syndrome.

Ring chromosome 14 and immunoglobulin locus

A 2.5-yr-old girl was evaluated for seizurelike episodes and psychomotor and growth retardation. Cytogenetic study showed a ring 14 chromosome in most cells, with some cells having monosomy 14. Rarely, a cell showed a double ring chromosome 14. Both parents had normal chromosomes. Because serum immunoglobulins have been mapped to the distal portion of 14q, we attempted to correlate Ig levels with the deletion involved in the formation of this ring. No decrease in IgG, IgM, IgA, IgE, and IgD serum levels was observed. The normal serum Ig levels found in the proposita are compatible with the suggestion that the Ig loci are not located on the terminal portion of 14q but more proximally in band 14q32. However, because Gm and Am allotyping was not available mapping was not conclusive.

Distal monosomy 14 not associated with ring formation

A 12-year-old boy with congenital heart disease, short stature, mildly dysmorphic facies, and mild intellectual impairment was found to have a de novo terminal deletion (14)(q32.3). Although his phenotype resembles that of six reported patients with a similar breakpoint, his CNS involvement is milder. He appears to be the first reported case of a terminal deletion of chromosome 14 not associated with ring 14 formation. Advanced parental ages and maternal origin of the chromosome with the deletion are noted.