IJMCM Autumn 2014, Vol 3, No 4

Case Report

Ring Chromosome 18: A Case Report Shermineh Heydari, Fahimeh Hassanzadeh, Mohammad Hassanzadeh Nazarabadi∗ Department of Medical Genetics, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Submmited 21 August 2014; Accepted 9 September 2014; Published 17 September 2014

Ring chromosomes are rare chromosomal disorders that usually appear to occur de novo. A ring chromosome forms when due to deletion both ends of chromosome fuse with each other. Depending on the amount of chromosomal deletion, the clinical manifestations may be different. So, ring 18 syndrome is characterized by severe mental growth retardation as well as microcephaly, brain and ocular malformations, hypotonia and other skeletal abnormalities. Here we report a 2.5 years old patient with a cleft lip, club foot, mental retardation and cryptorchidism. Chromosomal analysis on the basis of G-banding technique was performed following patient referral to the cytogenetic laboratory. Chromosomal investigation appeared as 46, XY, r(18) (p11.32 q21.32). According to the clinical features of such patients, chromosome investigation is strongly recommended. Key words: Ring chromosome 18, karyotyping, mental retardation

R

ing chromosomes from the cytogenetic point

result in the loss of terminal segments and genetic

of view are rare forms of chromosomal

material.

This

rearrangement

causes

partial

structure abnormalities (1, 2). The ring chromo-

monosomy of the distal region of both arms (3, 5).

some

human

Up to 2011 only 70 cases of ring chromosomes

chromosomes; their frequency is estimated to be

have been reported, in which among them, ring

between 1/30000 to 1/60000 (3) and almost 50

chromosome 18 was almost the most common

percent of all ring chromosomes originate from

(3, 5, 6).

has

been

reported

for

all

acrocentric chromosomes (2). Ring chromosomes

The phenotypic features of the ring chromo-

often occur de novo (1-4) and the incidence of

some 18 patients are similar to the features of the

inherited cases is 1 percent. On the other hand, 90

18 q deletion syndrome patients and a few of them

percent of these cases are of maternal origin; since

are similar to 18 p deletion or the combination of

ring chromosome will cause spermatogenesis

these two syndromes (4, 7). On the other hand,

abnormalities

patients with ring chromosomes often exhibit a

and

consequently

infertility

in

affected men (1, 2). The

form of

and

ring chromosome

depending on the size and the amount of the

formation is the occurrence of a break in both arms

euchromatin loss, the phenotype is variable (1, 2, 4,

and fusion of the breaking points together which

8). Therefore, the intensity of the phenotype



classic

general overlap in clinical manifestations

Corresponding author: Department of Medical Genetics, Mashhad University of Medical Sciences, Mashhad, Iran. Email: [email protected]

Heydari SH et al.

features depends on the size of chromosome

Therefore, this abnormality seems to have appeared

deletion, the stability of the rings, the presence of

de novo.

monosomy and other secondary aneuploidy cell lines, and the occurrence of mosaicism (8).

Discussion

The clinical manifestations of ring chromo-

Ring chromosomes 18 form when both ends

some 18 patients are include microcephaly, mild to

of the chromosome break and the broken sticky

severe mental retardation, short stature, obesity, mi-

ends fuse at the breakage point. During this process,

cropenis, cryptorchidism, hypertelorism, epicanthic

some of the genetic materials may be lost and

fold, microgenathia and small hands (7). Other

cause the clinical manifestations. GTG banding

manifestations include hypotonia, foot deformation,

karyotype in our patient revealed that the 18p11.32

proximally placed thumbs, arthritis/stenotic ear

and

canals, long tapering digits, abnormal male genita-

reports have presented ring chromosome 18

lia, flat midface, prominent antihelix antitragus and

as a rare and mostly appearing in mosaic form

carp - shaped mouth (4) as well as immunological

(1, 7). So far, one case of mosaic ring chromosome

problems (3, 6).

18

Case Report

patient

18q21.32

has

regions

were

been reported

revealed

a

in

phenotype

lost.

Previous

Iran (9).

Our

similar

with

Here we report a patient who is 2.5 years old

other reported cases (7, 10, 11), but the most

with a cleft lip, club foot, mild mental retardation

interesting finding which differenciates our finding

and have some changes in the genital region and the

with other investigations is the deletion of 18q21.33

testicles may not be fully descended (cryptor-

region. Databases such as NCBI and OMIM

chidism). He has punctured eardrum and uses

(*159430) show that an important gene called MBP

hearing aids.

(myelin basic protein) is located at this region. This

Chromosomal analysis was performed accor-

gene encodes a protein which is incorporated in

ding to standard procedures using GTG-banding.

oligodendrocytes and schwann cells myelin sheet

Peripheral blood lymphocytes were cultured in

(12). The correlation between the severe degrees of

RPMI 1640 medium (Gibco®) enriched with FBS,

mental retardation in patients with deletions

phytohemagglutinin and L-glutamine. The cells

proximal to 18q21.31, and milder forms in patients

were cultured for 72 hours at 37 °C in a CO2

with deletions distal to 18q21.33 was reported

incubator. Cultures were stopped by adding

(6).This finding is comparable with the result of

colcemid solution 2 hours before harvesting, then

Netzel et al. (13). Thus, in our patient, mental

the cells were exposed to hypotonic solution (KCl

retardation may be related to the deletion of both

0.075 M); fixed with methanol/ acetic acid (3:1)

18q21.32 region and MBP gene. Our finding also

(Vol/Vol). Metaphase chromosome spread was

demonstrate that in such cases, despite normal

prepared and G- banding technique was applied

parents' karyotype, chromosomal investigation is

with the use of trypsin-giemsa (GTG). A minimum

strongly recommended and may be informative as

of 50 metaphases were examined and all showed

well as other molecular cytogenetic techniques such

ring chromosome 18. Karyotypes were assigned

as FISH and CGH array which can help to achieve

according to the International System of Human

a better understanding of the mechanism of

Cytogenetic Nomenclature (ISCN) 2005.

ring chromosome 18 formation and clinical mani-

Chromosome analysis appeared as 46, XY, r(18) (p11.32 q21.32) (fig.1) whereas the parents karyotype appeared normal (46, XX and 46, XY).

festations. Acknowledgements We would like to express our appreciation to

Int J Mol Cell Med Autumn 2014; Vol 3 No 4 288

Ring Chromosome 18: A Case Report

Fig. 1. 2.5 years boy with ring chromosome 18. 46, XY, r (18) (p11.32 q21.32).

S. Mirzaee for her excellent technical assistance

child with neurological problems: mosaic ring chromosome18.

Conflict of interests

Eur J Pediatr 2008;167:655-9.

The authors declared no conflict of interests.

8. Sodre CP, Guilherme RS, Meloni VF. Ring chromosome instability evaluation in six patients with autosomal rings. Genet

Reference

Mol Res 2010;9:134-43.

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chromosome formation as a novel escape mechanism in patients

in a mentally retarded woman with mosaic ring chromosome 18.

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dup (18p)/del (18q) and r (18) mosaicism. J Hum Genet

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clinical, cytogenetic and molecular genetic studies on four

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patients. Int J Hum Genet 2004;4:197-200.

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5. Samli H, Özgöz A, Içduygu FM. A case with mosaic ring

polymorphism and multifunctionality of myelin basic protein.

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289 Int J Mol Cell Med Autumn 2014; Vol 3 No 4

Ladizhansky V, Boggs JM. Structural

Ring chromosome 18: a case report.

Ring chromosomes are rare chromosomal disorders that usually appear to occur de novo. A ring chromosome forms when due to deletion both ends of chromo...
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