A case of ring chromosome 2 with growth retardation, mild dysmorphism, and microdeletion of 2p detected using FISH

35-Year Follow-Up of a Case of Ring Chromosome 2: Array-CGH Analysis and Literature Review of the Ring Syndrome

Côté et al. [1981] suggested that ring chromosomes with or without deletions share a common pattern of phenotypic anomalies, regardless of which chromosome is involved. The phenotype of this 'general ring syndrome' consists of growth failure without malformations, few or no minor anomalies, and mild to moderate mental retardation. We reconsidered the ring chromosome 2 case previously published by Côté et al. [1981], and we characterized it by array CGH, polymorphic markers as well as subtelomere MLPA and FISH analysis. A terminal deletion (q37.3qter) of maternal origin of the long arm of the ring chromosome 2 was detected and confirmed by all the above-mentioned methods. Ring chromosome 2 cases are exceedingly rare. Only 18 cases, including the present one, have been published so far, and our patient is the longest reported survivor, with a 35-year follow-up, and the third case characterized by array-CGH analysis.

Clinico-radiological and molecular characterization of a child with ring chromosome 2 presenting growth failure, microcephaly, kidney and brain malformations

Background

Ring chromosome 2 is a rare constitutional abnormality that generally occurs de novo. About 14 cases have been described to date, but the vast majority of papers report exclusively conventional cytogenetic investigations and only two have been characterized by array-CGH.

Results

Here we describe the clinical, neuroradiological, and molecular features of a 5-year-old boy harbouring a ring chromosome 2 presenting with severe growth failure, facial and bone dysmorphisms, microcephaly, and renal malformation. Brain MR with diffusion tensor imaging revealed simplified cortical gyration, pontine hypoplasia, and abnormally thick posterior corpus callosum, suggesting an underlying axonal guidance defect. Cytogenetic investigations showed a karyotype with a ring chromosome 2 and FISH analysis with subtelomeric probes revealed the absence of signals on both arms. These results were confirmed by array-CGH showing terminal deletions on 2p25.3 (~439 kb) and 2q37.3 (~3.4 Mb).

Conclusions

Our report describes a new patient with a ring chromosome 2 completely characterised by array-CGH providing additional information useful not only to study genotype-phenotype correlation but also to validate the role of already reported candidate genes and to suggest novel ones which could improve our understanding of the clinical features associated with ring chromosome 2.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-015-0121-z) contains supplementary material, which is available to authorized users.

A new patient with a terminal de novo 2p25.3 deletion of 1.9 Mb associated with early-onset of obesity, intellectual disabilities and hyperkinetic disorder

Terminal and interstitial deletions of 2p25.3 (size < Mb), detected by array-CGH analysis, have been reported in about 18 patients sharing common clinical features represented by early-onset obesity/ overweightness associated with intellectual disabilities (ID) and behavioural troubles. This observations led to hypothesize that 2p subtelomeric deletion should be associated with syndromic obesity and MYT1L became the main candidate gene for ID and obesity since it is deleted or disrupted in all hitherto published cases.

Here we described a 2p25.3 de novo terminal deletion of 1.9 Mb, of paternal origin, detected by array-CGH analysis in a girl of 4.4 years with a distinctive phenotype consisting of early-onset of obesity associated with moderate ID, and hyperkinetic disorder. The deletion disrupted MYT1L and encompassed five other OMIM genes, ACP1, TMEM18, SNTG2, TPO, and PXDN.

Here, we discuss the combined functional effects of additional haploinsufficient genes, that may concur with heterozygous deletion of MYT1L, in the aetiology for syndromic obesity associated with 2p25.5 subtelomeric deletion.

Ring 2 chromosome associated with failure to thrive, microcephaly and dysmorphic facial features

We report here a child with a ring chromosome 2 [r(2)] associated with failure to thrive, microcephaly and dysmorphic features. The chromosomal aberration was defined by chromosome microarray analysis, revealing two small deletions of 2p25.3 (139 kb) and 2q37.3 (147 kb). We show the clinical phenotype of the patient, using a conventional approach and the molecular cytogenetics of a male with a history of prenatal intrauterine growth restriction (IUGR), failure to thrive, microcephaly and dysmorphic facial features. The phenotype is very similar to that reported in other clinical cases with ring chromosome 2.

Prenatal diagnosis of ring chromosome 2 with lissencephaly and 2p25.3 and 2q37.3 microdeletions detected using array comparative genomic hybridization

We present rapid aneuploidy diagnosis of ring chromosome 2 with 2p25.3 and 2q37.3 microdeletions by aCGH using uncultured amniocytes in a fetus with IUGR, microcephaly, lissencephaly and ambiguous external genitalia. Our case adds lissencephaly to the list of CNS abnormalities in ring chromosome 2 with 2p25.3 and 2q37.3 microdeletions. We discuss the consequence of haploinsufficiency of HDAC4, KIF1A, PASK, HDLBP, FRAP2 and D2HGDH on 2q37.3, and haploinsufficiency of MYT1L, SNTG2 and TPO on 2p25.3 in this case.

De novo interstitial deletion of chromosome 2 (p23p24)

Structural anomalies associated with partial 2p monosomy are rare. There has only been one case of interstitial deletion of 2p24.2-2p25.1 and three cases of 2p23.3-2p25.1 described in the literature. We report here the first instance of an interstitial deletion of 2p23p24, confirmed by comparative genome hybridization. We present a clinical and cytogenetic report of a patient with psychomotor retardation, hearing impairment, and limb abnormalities. The obvious osseous fusion with bone marrow and cortex continuation between proximal parts of radius and ulna-congenital radioulnar synostosis-were first visualized by multidetector-row computed tomography scan.

Ring chromosome 12 with inverted microduplication of 12p13.3 involving the Von Willebrand Factor gene associated with cryptogenic stroke in a young adult male

We report a 35-year-old male with a ring chromosome 12 originally diagnosed 20 years prior to presentation with an ischemic stroke. Array CGH analysis revealed a sub-microscopic microdeletion and microduplication within 12p13.3 and a microdeletion in 12q24.33. FISH analysis further revealed that the duplication was in an inverted orientation and included exons 35-52 of the dosage-sensitive Von Willebrand Factor (VWF) gene. Partial duplication of this gene, which has a role in the clotting cascade, suggests a potential mechanism for generating a pro-thrombotic state that may have contributed to a premature cerebrovascular event. Evidence of raised VWF antigen levels and VWF activity levels in the highest quartile provides support for this hypothesis. This case illustrates that when a ring chromosome is identified, the possibility of cryptic genomic rearrangements needs to be considered as these may have implications in predicting natural history.

Deletion 2p25.2: a cryptic chromosome abnormality in a patient with autism and mental retardation detected using aCGH

We describe a 7-year-old patient with autism, moderate mental retardation, secondary microcephaly, agenesis of right optic nerve, and dysmorphic features carrying a de novo cryptic deletion of chromosome 2p25.2, detected by aCGH. Pure monosomies of 2p are very rare, and are usually observed as part of more complex aberrations involving other chromosomes. To the best of our knowledge, this is the first case presenting with a severe clinical phenotype and a de novo pure deletion of 2p25.2. The phenotypic effects of this rearrangement and the role of SOX11 gene, removed in our case, are herein discussed.

Recurrent inverted duplication of 2p with terminal deletion in a patient with the classical phenotype of trisomy 2p23-pter

Inverted duplications with terminal deletions have been reported in an increasing number of chromosomes and are probably more frequent than suspected until recently. We describe the cytogenetic and molecular characterization of an inverted duplication of chromosome 2p in an 8-year-old girl. Firstly interpreted as partial duplication 2p, the rearrangement was in fact an inverted duplication associated with a terminal deletion of the short arm of the rearranged chromosome 2, the latter not being detectable by cytogenetic analysis. The complete karyotype was: 46,XX,add(2)(p23)dn.ish inv dup del(2)(:p23.2-->p25.3::p25.3-->qter) (wcp2+,N-MYC++,2pter-)dn. We precisely define the extension of both the duplication and the deletion using bacterial artificial chromosomes clones spanning the regions. The size of the inverted duplicated segment was estimated to be 28 Mb, spanning from 2p23.2 to 2p25.3, and an approximately 1.6 Mb segment at 2pter-p25.3 was deleted in the abnormal chromosome. The physical findings noted in our patient include prominent forehead, hypertelorism, flat nasal bridge, and low-set and large ears. In addition, she had congenital heart defect and scoliosis. Her psychomotor development was severely delayed from the beginning. All these clinical features are the same as observed for the typical trisomy 2p23-pter syndrome. The phenotypic effects of the terminal deletion of 2p in addition to the trisomy are discussed. This is the third patient presenting with a severe clinical phenotype and a de novo inv dup del (2p).

Mosaic ring 20 with no detectable deletion by FISH analysis: Characteristic seizure disorder and literature review

Ring chromosome 20 is a rare chromosome disorder characterized by a typical seizure phenotype consisting of complex partial seizures, frequent progression to generalized tonic or tonic-clonic seizures, and nocturnal frontal lobe seizures with frequent episodes of non-convulsive status epilepticus. Development may be normal or mildly delayed, followed by cognitive and behavioral decline after seizure onset. Here, we describe a patient with a typical severe seizure phenotype and a mosaic ring chromosome 20 without loss of p or q subtelomere regions or telomeric sequences. The ring had a longer telomere length than either of the telomere ends of its homologous chromosome 20 by quantitative fluorescence in situ hybridization analysis, suggesting that it might be derived from telomere-telomere fusion. The phenotypic comparison of this patient and other chromosome 20 cases that had terminal deletions of 20qter (n = 1) and 20pter (n = 7), shows that the epilepsy phenotype and electroencephalographic abnormalities are characteristic in patients with ring chromosome 20. Several hypotheses have been proposed to address the elusive mechanisms underlying the seizure disorder in ring chromosome 20. These possibilities include haploinsufficiency of two epilepsy genes CHRNA4 and KCNQ2 located at 20qter, silencing of these genes by a telomere position effect, or microdeletions or rearrangements of genetic material during the ring formation.