Ring chromosome

About: Ring chromosome is a research topic. Over the lifetime, 1546 publications have been published within this topic receiving 31061 citations. The topic is also known as: supernumerary circular chromosome.

Characterization of two supernumerary marker chromosomes in a patient with signs of Klinefelter syndrome, mild facial anomalies, and severe speech delay.

Abstract: A boy with signs of Klinefelter syndrome, mild facial dysmorphic features, and severely retarded speech development displayed a female karyotype with mosaicism for two marker chromosomes 48,XX,+mar1,+mar2[68]/47,XX,+mar1[19]/47,XX,+mar2[6]/46,XX[8]. Using chromosomal microdissection, locus-specific fluorescence in situ hybridization (FISH), and PCR with several Y-chromosome markers, the larger supernumerary marker chromosome (SMC) was characterized as a ring Y-chromosome. Detection of the SRY-region explained the male phenotype. The smaller second marker chromosome contained the pericentromeric region of chromosome 8. We suggest that the co-occurrence of a partial Y-chromosome and partial trisomy 8 explain the severe speech delay and the facial dysmorphic features.

Prenatal diagnosis of a de novo ring chromosome 11.

Abstract: Ring chromosomes are uncommon findings in prenatal diagnosis. Growth retardation is the most significant manifestation, in particular among patients with rings of larger chromosomes. A 30-year-old gravida 1, para 0 white woman was referred for genetic counseling because of maternal anxiety. Cytogenetic analysis of amniotic fluid cells at 16 weeks gestation revealed an abnormal mosaic female chromosome complement; 46,XX,r(11)(p15q25)[14]/45,XX,-11[7]. The ring 11 showed no detectable loss of chromosomal material at 450 band level. Both parents had a normal karyotype. Fluorescence in situ hybridization demonstrated intact subtelomeric regions in the ring chromosome. A targeted ultrasound evaluation at the time of consultation suggested no significant abnormalities. The parents were counseled and subsequently decided to terminate the pregnancy. The autopsy revealed an immature female fetus with abnormal craniofacial features including brachycephaly, low-set ears and hypertelorism, bicornuate uterus, and calcifications in the renal tubules. The abnormal phenotypes could be a consequence of the ring instability, submicroscopic deletion, and/or alteration of genetic material at the site of fusion.

Atypical teratoid rhabdoid brain tumor in an infant with ring chromosome 22

Abstract: Reports of constitutional ring chromosome 22, r(22) are rare. Individuals with r(22) present similar features as those with the 22q13 deletion syndrome. The instability in the ring chromosome contributes to the development of variable phenotypes. Central nervous system (CNS) atypical teratoid rhabdoid tumors (ATRTs) are rare, highly malignant tumors, primarily occurring in young children below 3 years of age. The majority of ATRT cases display genetic alterations of SMARCB1 (INI1/hSNF5), a tumor suppressor gene located on 22q11.2. The coexistence of a CNS ATRT in a child with a r(22) is rare. We present a case of a 4-month-old boy with 46,XY,r(22)(p13q13.3), generalized hypotonia and delayed development. High-resolution microarray analysis revealed a 3.5-Mb deletion at 22q13.31q13.33. At 11 months, the patient had an ATRT (5.6 cm×5.0 cm×7.6 cm) in the cerebellar vermis, which was detected in the brain via magnetic resonance imaging.

Chimeras for Genetic Analysis

Abstract: A chimera—defined as an individual (plant) composed of two or more genotypes— usually results from any heritable change that provides different expression by the descendants of two daughter cells from a mitotic cell division. Chimeras can be very useful in revealing the action of mutant genes in plants. McClintock (1938) first demonstrated the feasibility of using deficiencies and unstable ring chromosomes to study the consequences of the absence of functional genes in homozygous mutant tissue. Stadler and Roman (1948) identified three previously unknown genes near the a1 locus by uncovering different lengths of X-ray induced deficiencies (a-x1, a-x2, a-x3) with an unstable fragment (A-b Frag) carrying functional genes located in the deficiency segments. Similar studies by McClintock (1951, 1965), Steffensen (1968), Coe and Neuffer (1978), and Johri and Coe (1983) demonstrate the utility of this approach in solving problems in biology. An advantage of chimeras in genetic research is that they provide mutant tissue that is of identical age and supported by adjoining normal tissue; this allows expression of lethal mutants that would not normally be observable. Chimeras may arise spontaneously for unspecified reasons or they may be produced by unstable chromosome configurations (inversions, rings, centric fragments, monosomics), by chromosome breaking agents (radiation or chemicals) or by unstable loci resulting from transposon insertion (Ds, etc.). Analysis of chimeras can tell us that some genes encode phenotypes that are cell autonomous (anthocyanin and chlorophyll genes) and that some are not (andromonoecious dwarfing). They also (1) show that some lethal mutants may be rescued by supplying missing chemicals, (2) indicate the developmental pattern of the plant parts, and (3) provide clues as to the sequence of events in a biosynthetic pathway.