Balkan Journal of Medical Genetics

MOLECULAR ANALYSIS OF RING Y CHROMOSOME IN A 10-YEAR-OLD BOY WITH MIXED GONADAL DYSGENESIS AND GROWTH HORMONE DEFICIENCY
Milenkovic T1,*, Guc-Scekic M2, Zdravkovic D1,3, Topic V4, Liehr T5, Joksic G6, Radivojevic D2, Lakic N2
*Corresponding Author: Tatjana Milenkovic, Department of Endocrinology, Institute for Mother and Child Healthcare of Serbia “Dr. Vukan Cupic,” Radoja Dakica 6-8, 11 070 Belgrade, Serbia; Tel.: +381-11-3018-109; Fax: +381-11-3108-257; E-mail: tanjamil@eunet.rs
page: 71

RESULTS

Karyotype analysis of G-banded lymphocyte chromosomes revealed a 45,X karyotype in 24/44 (54.5%) cells, a normal number of chromosomes with a small, dot-like ring chromosome in 17/44 (38.6%) cells, and 47 chromosomes with two ring chromosomes (Figure 1A and 1B) in 3/44 (6.8%) cells. We considered the small ring chromosome to have originated from the Y chromosome and described the patient’s karyotype as: mos 45,X[24]/46,X, r(?Y)[17]/47,X, r(?Y)x2[3]. Parental karyotypes were normal. The C-banding analysis of the heterochromatic Yqh region of the patient and his father showed the loss of this region in the patient and its presence in the father, suggesting a de novo origin of the ring chromosome. Fluorescent in situ hybridization using a Y chromosome centromeric α satellite probe demonstrated the absence of a fluorescent signal in 31/100 cells and the presence of one (19/100) and two (2/100) fluorescent signals in interphase nuclei and metaphase cells (Figure 1C and 1D). When a Y chromosome centromeric α satellite probe was used, one fluorescent signal was found on the ring Y chromosome, confirming its monocentric nature. The somatic karyotype was therefore described as: 45,X[31]/46,X.ishr(Y) (DYZ1+) [19]/ 47,X.ish r(Y) x2(DYZ1x2)[2]. SubcenM-FISH [25] characterized two ring (Y) variants in the patient’s karyotype: ish r(Y)(RP11- 115H13+, cepY+,RP11.71M14+) and ishr(Y;Y)(RP11- 115H13++, cepY++,RP11.71M14++) (Figure 2A). These were present in different combinations in at least three cellular subpopulations: 46,X,r(Y);47,X,r(Y)x2; 47,X,r(Y)+r(Y;Y). The additional ring (Y;Y) variant, found in only one cell, was a ring chromosome in the process of forming a double ring. Telo-FISH displayed an r(Y) chromosome with no telomeric signals (Figure 2C), thus confirming loss of telomeric regions on Yp and Yq. Fluorescent in situ hybridization with the subtelomeric probe Xp/Yp and probe for Yq12, demonstrated the presence of the Yp subtelomeres and deletion of Yq12 region on the r(Y). The double Y chromosome r(Y;Y) showed two signals for the Yp subtelomere region (Figure 2B). Polymerase chain reaction with primers for the heterochromatic region of the Y chromosome revealed that the whole of this Yq12 region was missing. Multiplex PCR with selected primers for AZF (the AZFa, AZFb and AZFc) region, SRY and ZFY/ZFX genes showed their presence (Figure 3). These results confirmed the presence of two breakpoints on the Y chromosome that led to formation of the ring: one on the Yp arm (between the subtelomeric region and the telomere) and the other on the Yq arm at Yq12.

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