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

An Extremely Rare Case of Birk-Barel Syndrome With Severe Central Apneas

Birk-Barel syndrome, alternatively known as KCNK9 imprinting syndrome, is caused by a missense mutation in the potassium two pore domain channel subfamily K member 9 (KCNK9) gene on chromosome 8q24.3. This syndrome demonstrates dominant inheritance and is imprinted with paternal silencing, where the paternally inherited allele is silenced, and the maternally inherited allele is active. Congenital hypotonia, palatal abnormalities, intellectual disability, severe feeding difficulties, and dysmorphic facial features characterize this sporadic genetic syndrome. To date, there are approximately 21 molecularly diagnosed individuals worldwide described in the literature. We describe the first known case of Puerto Rican ethnicity, a 16-month-old female born prematurely at 36-weeks with Birk-Barel syndrome, confirmed with whole-exome sequencing, and her response to non-invasive ventilation as a treatment for her sleep breathing disorder.

Complex biology of constitutional ring chromosomes structure and (in)stability revealed by somatic cell reprogramming

Human ring chromosomes are often unstable during mitosis, and daughter cells can be partially or completely aneuploid. We studied the mitotic stability of four ring chromosomes, 8, 13, 18, and 22, in long-term cultures of skin fibroblasts and induced pluripotent stem cells (iPSCs) by GTG karyotyping and aCGH. Ring chromosome loss and secondary aberrations were observed in all fibroblast cultures except for r(18). We found monosomy, fragmentation, and translocation of indexed chromosomes. In iPSCs, aCGH revealed striking differences in mitotic stability both between iPSC lines with different rings and, in some cases, between cell lines with the same ring chromosome. We registered the spontaneous rescue of karyotype 46,XY,r(8) to 46,XY in all six iPSC lines through ring chromosome loss and intact homologue duplication with isoUPD(8)pat occurrence, as proven by SNP genotype distribution analysis. In iPSCs with other ring chromosomes, karyotype correction was not observed. Our results suggest that spontaneous correction of the karyotype with ring chromosomes in iPSCs is not universal and that pluripotency is compatible with a wide range of derivative karyotypes. We conclude that marked variability in the frequency of secondary rearrangements exists in both fibroblast and iPSC cultures, expanding the clinical significance of the constitutional ring chromosome.