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46,XY,r(8)/45,XY,-8 Mosaicism as a Possible Mechanism of the Imprinted Birk-Barel Syndrome: A Case Study.

ABSTRACT: Ring chromosome 8 (r(8)) is one of the least frequent ring chromosomes. Usually, maternal chromosome 8 forms a ring, which can be lost from cells due to mitotic instability. The 8q24 region contains the imprinted KCNK9 gene, which is expressed from the maternal allele. Heterozygous KCNK9 mutations are associated with the imprinting disorder Birk-Barel syndrome. Here, we report a 2.5-year-old boy with developmental delay, microcephaly, dysmorphic features, diffuse muscle hypotonia, feeding problems, motor alalia and noncoarse neurogenic type of disturbance of muscle electrogenesis, partially overlapping with Birk-Barel syndrome phenotype. Cytogenetic analysis of lymphocytes revealed his karyotype to be 46,XY,r(8)(p23q24.3)[27]/45,XY,-8[3]. A de novo 7.9 Mb terminal 8p23.3p23.1 deletion, a 27.1 Mb 8p23.1p11.22 duplication, and a 4.4 Mb intact segment with a normal copy number located between them, as well as a 154-kb maternal LINGO2 gene deletion (9p21.2) with unknown clinical significance were identified by aCGH + SNP array. These aberrations were confirmed by real-time PCR. According to FISH analysis, the 8p23.1-p11.22 duplication was inverted. The ring chromosome originated from maternal chromosome 8. Targeted massive parallel sequencing did not reveal the KCNK9 mutations associated with Birk-Barel syndrome. Our data allow to assume that autosomal monosomy with inactive allele of imprinted gene arising from the loss of a ring chromosome in some somatic cells may be an etiological mechanism of mosaic imprinting disorders, presumably with less severe phenotype.

SUBMITTER: Kashevarova AA

PROVIDER: S-EPMC7763634 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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46,XY,r(8)/45,XY,-8 Mosaicism as a Possible Mechanism of the Imprinted Birk-Barel Syndrome: A Case Study.

Kashevarova Anna A AA Nikitina Tatyana V TV Mikhailik Larisa I LI Belyaeva Elena O EO Vasilyev Stanislav A SA Lopatkina Mariya E ME Fedotov Dmitry A DA Fonova Elizaveta A EA Zarubin Aleksei A AA Sivtsev Aleksei A AA Skryabin Nikolay A NA Nazarenko Lyudmila P LP Lebedev Igor N IN

Genes 20201209 12

Ring chromosome 8 (r(8)) is one of the least frequent ring chromosomes. Usually, maternal chromosome 8 forms a ring, which can be lost from cells due to mitotic instability. The 8q24 region contains the imprinted <i>KCNK9</i> gene, which is expressed from the maternal allele. Heterozygous <i>KCNK9</i> mutations are associated with the imprinting disorder Birk-Barel syndrome. Here, we report a 2.5-year-old boy with developmental delay, microcephaly, dysmorphic features, diffuse muscle hypotonia, ...[more]

PMID: 33316910

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Project description:Partial and mixed gonadal dysgenesis (PGD and MGD) are characterized by genital ambiguity and the finding of either a streak gonad and a dysgenetic testis or two dysgenetic testes. The karyotype in PGD is 46,XY, whereas a 45,X/46,XY mosaicism or its variants (more than two lineages and/or structural abnormalities of the Y chromosome) is generally found in MGD. Such mosaics are also compatible with female phenotype and Turner syndrome, ovotesticular disorder of sex development, and infertility in men with normal external genitalia. During the last few years, evidences of a linkage between Y microdeletions and 45,X mosaicism have been reported. There are also indications that the instability caused by such deletions might be more significant in germ cells. The aim of this work was to investigate the presence of Y chromosome microdeletions in individuals with PGD and in those with 45,X/46,XY mosaicism or its variants and variable phenotypes.Our sample comprised 13 individuals with PGD and 15 with mosaicism, most of them with a MGD phenotype (n?=?11). Thirty-six sequence tagged sites (STS) spanning the male specific region (MSY) on the Y chromosome (Yp, centromere and Yq) were analyzed by multiplex PCR and some individual reactions.All STS showed positive amplifications in the PGD group. Conversely, in the group with mosaicism, six individuals with MGD had been identified with Yq microdeletions, two of them without structural abnormalities of the Y chromosome by routine cytogenetic analysis. The deleted STSs were located within AZFb and AZFc (Azoospermia Factor) regions, which harbor several genes responsible for spermatogenesis.Absence of deletions in individuals with PGD does not confirm the hypothesis that instability of the Y chromosome in the gonads could be one of the causes of such condition. However, deletions identified in the second group indicate that mosaicism may be associated with Y chromosome abnormalities detectable only at the molecular level. If patients with mosaicism and Y microdeletions reared as males decide to undergo in vitro fertilization, Y chromosomes which tend to be unstable during cell division may be transmitted to offspring.

Dataset Information

46,XY,r(8)/45,XY,-8 Mosaicism as a Possible Mechanism of the Imprinted Birk-Barel Syndrome: A Case Study.

Publications

46,XY,r(8)/45,XY,-8 Mosaicism as a Possible Mechanism of the Imprinted Birk-Barel Syndrome: A Case Study.

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