Five cases of supernumerary small ring chromosomes 1: Heterogeneity and genotype–phenotype correlation

Koolen-de Vries syndrome in a 63-year-old woman: Report of the oldest patient and a review of the adult phenotype

Koolen-de Vries syndrome (KdVS) is a rare genetic disorder caused by a de novo microdeletion in chromosomal region 17q21.31 encompassing KANSL1 or by a de novo intragenic pathogenic variant of KANSL1. KdVS is typically characterized by intellectual disability (ID), variable from mild to severe, developmental psychomotor delay, especially of expressive language development, friendly disposition, and multiple systemic abnormalities. So far, most of the individuals affected by KdVS are diagnosed in infancy or in adolescence; to the best of our knowledge, only 34 (including ours) adults have been reported in literature. Here we present the adult phenotype of a 63-year-old Italian woman affected by KdVS, caused by a 17q21.31 microdeletion. She is, to our knowledge, the oldest affected individual reported so far. We collected her clinical history and photographs, as well as those of other 26 adult patients described so far and compared her to them. We propose that the cardinal features of KdVS in adulthood are ID (ranging from mild to severe, usually moderate), friendly behavior, musculoskeletal abnormalities (especially scoliosis), and facial dysmorphism (a long face and a pronounced pear-shape nose with bulbous overhanging nasal tip). Therefore, we suggest considering KdVS in differential diagnosis in adult patients characterized by these features.

Ring chromosomes: from formation to clinical potential

Ring chromosomes (RCs) are circular DNA molecules, which occur rarely in eukaryotic nuclear genomes. Lilian Vaughan Morgan first described them in the fruit fly. Human embryos very seldom have RCs, about 1:50,000. Carriers of RCs may have varying degrees of symptoms, from healthy phenotype to serious pathologies in physical and intellectual development. Many authors describe common symptoms of RC presence: short stature and some developmental delay that could be described as a "ring chromosome syndrome." As a rule, RCs arise de novo through the end-joining of two DNA double-strand breaks, telomere-subtelomere junction, or inv dup del rearrangement in both meiosis and mitosis. There are family cases of RC inheritance. The presence of RCs causes numerous secondary chromosome rearrangements in vivo and in vitro. RCs can change their size, become lost, or increase their copy number and cause additional deletions, duplication, and translocations, affecting both RCs and other chromosomes. In this review, we examine RC inheritance, instability, mechanisms of formation, and potential clinical applications of artificially created RCs for large-scale chromosome rearrangement treatment.

Another patient with 12q13 microduplication

Interstitial duplication of the long arm of chromosome 12 is a rare cytogenetic condition. While several reports describe distal 12q duplication, only one case report of homogeneous, non-mosaic interstitial 12q13 duplication has been documented to date. The authors of that observation proposed that the associated phenotype represented a phenocopy of Wolf-Hirschhorn syndrome [Dallapiccola et al., 2009]. Only a few other recorded patients with deletion 12q13 → 12q21 involved mosaicism. We describe a new patient with homogeneous 12q13 duplication in a 6-year-old girl who, in early infancy, presented with dysmorphic features suggesting Wolf-Hirschhorn syndrome. What is potentially significant about this patient is that her facial phenotype evolved with age, suggesting a different gestalt in older patients.

Implications of prenatal diagnosis of the fetus with both interstitial deletion and a small marker ring originating from chromosome 5

We describe a patient with 47,XY,del(5)(p11p13), +mar observed in prenatal screening. We performed analyses including G-banding, multi-color fluorescent in situ hybridization (mFISH) for fetal chromosome detection. After birth array-based comparative genomic hybridization (aCGH), bacterial artificial chromosome (BAC)-FISH was carried out to define the chromosomal changes precisely. The mFISH revealed that a ring chromosome that had originated from chromosome 5. The aCGH showed that this fetus had a terminal duplication, an interstitial deletion, and a pericentromeric duplication of the short arm of chromosome 5. This complex alteration resulted in partial trisomy 5p15.33-p15.31, partial monosomy 5p14.3-p13.2, and partial trisomy 5p12-p11. To clarify these alterations, we performed BAC-FISH using BAC clones related to deleted and duplicated regions, and found that a derivative (der) chromosome 5 showed the presence of hybridization signals from the duplicated region at 5p15.33 and the loss of hybridization signals from the deleted region at 5p14.2. In addition, FISH analysis confirmed the origin of the marker chromosome. Hybridization signals from the second intervening sequence at 5p13.1, between the deleted region and the pericentric duplicated region, were present on the marker ring chromosome.

Mosaic supernumerary ring chromosome 1 in a three-generational family: 10-year follow-up report

Additional small ring chromosome 1 is described with increasing rate of mosaicism in three generations. Ten years after the first examination, the mosaic rates in the patients were strikingly similar. An increase in the expression of phenotypic anomalies was also observed in the successive generations. FISH examinations following microdissection revealed signals which were positive for 1p13 and 1q21 indicating that the ring contained euchromatic segments on both ends. Additionally, array-CGH whole-genome analysis showed a single copy gain corresponding to band 1p12 to band 1q21-1 of chromosome 1 in the patients. The presence of euchromatic material from chromosome 1 in the ring suggests that the relationship between the cytogenetic findings and the clinical manifestation is likely causative. These unique observations might be explained by mitotic loss of the ring at early embryogenesis, and would indicate different mitotic vulnerability of certain chromosome abnormalities at early postzygotic stages versus later during development.

Association of syndromic mental retardation with an Xq12q13.1 duplication encompassing the oligophrenin 1 gene

OPHN1 mutations cause a syndromic form of mental retardation (MR) characterized by cerebellar hypoplasia, early hypotonia, motor and speech delay, with occasional seizures and strabismus. Here we report on a familial chromosome duplication spanning about 800 Kb of Xq12q13.1, associated with MR and a distinctive phenotype in the affected male, but not in his heterozygous mother. The parents were healthy and non-consanguineous with a history of three pregnancies. The first resulted in the birth of a boy with MR, motor impairment and seizures. The second pregnancy was terminated because of trisomy 18. At the time of the third, the first affected boy was analyzed by array-CGH, which revealed a 800 Kb duplication at Xq12q13.1, encompassing three genes, including OPHN1. This mutation was inherited from his healthy mother and was not present in any of the three maternal brothers. To our knowledge this is the first report of a clinical phenotype associated with duplication of Xq12q13.