[Molecular cytogenetic study of a case with ring chromosome 15]

To explore the genetic basis for a patient featuring developmental delay.

The patient and her parents were subjected to G- and C-banded chromosomal karyotyping analysis. The proband was also analyzed by single nucleotide polymorphism microarray (SNP-array). The result was verified by using fluorescence quantitative PCR (qPCR).

The proband's karyotype was ascertained as 46,XX, r(15)(p11.2q26.3)[92]/45,XX,-15[9]/46,XX, dic r(15)(p11.2q26.3;p11.2q26.3)[4]. SNP-array revealed that she has carried a de novo deletion at 15q26.3 (98 957 555-102 429 040) spanning approximately 3.4 Mb, which encompassed the IGF1R gene. qPCR has confirmed haploinsufficiency of exons 3, 10 and 20 of the IGF1R gene. Both of her parents had a normal karyotype.

The abnormal phenotype of the proband may be attributed to the microdeletion at 15q26.3, in particular haploinsuffiency of the IGF1R gene and instability of the ring chromosome. Cytogenetic method combined with SNP-array and qPCR can efficiently delineate chromosomal aberrations and provide accurate information for clinical diagnosis and genetic counseling.