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

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.

A mosaic intragenic microduplication of LAMA1 and a constitutional 18p11.32 microduplication in a patient with keratosis pilaris and intellectual disability.

The application of array-based comparative genomic hybridization and next-generation sequencing has identified many chromosomal microdeletions and microduplications in patients with different pathological phenotypes. Different copy number variations are described within the short arm of chromosome 18 in patients with skin diseases. In particular, full or partial monosomy 18p has also been associated with keratosis pilaris. Here, for the first time, we report a young male patient with intellectual disability, diabetes mellitus (type I), and keratosis pilaris, who exhibited a de novo 45-kb microduplication of exons 4-22 of LAMA1, located at 18p11.31, and a 432-kb 18p11.32 microduplication of paternal origin containing the genes METTL4, NDC80, and CBX3P2 and exons 1-15 of the SMCHD1 gene. The microduplication of LAMA1 was identified in skin fibroblasts but not in lymphocytes, whereas the larger microduplication was present in both tissues. We propose LAMA1 as a novel candidate gene for keratosis pilaris. Although inherited from a healthy father, the 18p11.32 microduplication, which included relevant genes, could also contribute to phenotype manifestation.

Compound phenotype in a girl with r(22), concomitant microdeletion 22q13.32-q13.33 and mosaic monosomy 22.

BACKGROUND: Ring chromosome instability may influence a patient's phenotype and challenge its interpretation. RESULTS: Here, we report a 4-year-old girl with a compound phenotype. Cytogenetic analysis revealed her karyotype to be 46,XX,r(22). aCGH identified a 180 kb 22q13.32 duplication, a de novo 2.024 Mb subtelomeric 22q13.32-q13.33 deletion, which is associated with Phelan-McDermid syndrome, and a maternal single gene 382-kb TUSC7 deletion of uncertain clinical significance located in the region of the 3q13.31 deletion syndrome. All chromosomal aberrations were confirmed by real-time PCR in lymphocytes and detected in skin fibroblasts. The deletions were also found in the buccal epithelium. According to FISH analysis, 8% and 24% of the patient's lymphocytes and skin fibroblasts, respectively, had monosomy 22. CONCLUSIONS: We believe that a combination of 22q13.32-q13.33 deletion and monosomy 22 in a portion of cells can better define the clinical phenotype of the patient. Importantly, the in vivo presence of monosomic cells indicates ring chromosome instability, which may favor karyotype correction that is significant for the development of chromosomal therapy protocols.