Background
The proximal long arm of chromosome 15 (15q) contains repeat sequences that are prone to misalignments and unequal crossover during meiosis, leading to deletions, duplications, and supernumerary chromosomes [1-4]. Deletions of 15q11q13 involving the Prader-Willi/Angelman syndrome critical region (PWACR) may cause Prader-Willi syndrome [MIM 176270] and Angelman syndrome [MIM 105830], depending on the parental origin [1]. Duplications of 15q11q13, particularly of maternal origin, are associated with clinical features, including psychomotor delays, cognitive disability, epilepsy, growth retardation, and behavioral problems [3,5]. Derivative chromosomes 15q, mostly in a form of inverted duplication of 15q (inv dup(15q)), are the most common supernumerary marker chromosomes (SMC) in humans [2,6,7]. Because of their clinical relevance, SMC15s spanning PWACR have been the focus of studies. Clinical features associated with tetrasomy 15q11q13 have been reported but the underlying molecular characteristics have not been well characterized [2]. In contrast, aneusomies resulting in high copy number (≥ 4 copies) 15q11q13 segment, particularly greater than four copies, are rare. So far, only a dozen of hexasomy 15q11q13 cases have been reported in the literature and none were pentasomy 15q11q13 [4,8]. All of the patients with high copy number 15q11q13 reported thus far are from the West populations.
Most high copy number 15q11q13 aneusomies were studied by chromosome banding and fluorescence in situ hybridization (FISH), only few were analyzed at molecular levels. Recent advances in high density cytogenomic arrays provide powerful tools in detecting submicroscopic copy number change and delineating chromosome breakpoints. Here, we report a study of two Han Chinese patients with tetrasomy and pentasomy 15q11q13 who present with developmental delays and cognitive disabilities.
Background
The proximal long arm of chromosome 15 (15q) contains repeat sequences that are prone to misalignments and unequal crossover during meiosis, leading to deletions, duplications, and supernumerary chromosomes [1-4]. Deletions of 15q11q13 involving the Prader-Willi/Angelman syndrome critical region (PWACR) may cause Prader-Willi syndrome [MIM 176270] and Angelman syndrome [MIM 105830], depending on the parental origin [1]. Duplications of 15q11q13, particularly of maternal origin, are associated with clinical features, including psychomotor delays, cognitive disability, epilepsy, growth retardation, and behavioral problems [3,5]. Derivative chromosomes 15q, mostly in a form of inverted duplication of 15q (inv dup(15q)), are the most common supernumerary marker chromosomes (SMC) in humans [2,6,7]. Because of their clinical relevance, SMC15s spanning PWACR have been the focus of studies. Clinical features associated with tetrasomy 15q11q13 have been reported but the underlying molecular characteristics have not been well characterized [2]. In contrast, aneusomies resulting in high copy number (≥ 4 copies) 15q11q13 segment, particularly greater than four copies, are rare. So far, only a dozen of hexasomy 15q11q13 cases have been reported in the literature and none were pentasomy 15q11q13 [4,8]. All of the patients with high copy number 15q11q13 reported thus far are from the West populations.
Most high copy number 15q11q13 aneusomies were studied by chromosome banding and fluorescence in situ hybridization (FISH), only few were analyzed at molecular levels. Recent advances in high density cytogenomic arrays provide powerful tools in detecting submicroscopic copy number change and delineating chromosome breakpoints. Here, we report a study of two Han Chinese patients with tetrasomy and pentasomy 15q11q13 who present with developmental delays and cognitive disabilities.
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