A de novo marker chromosome 15 in a child with isolated developmental delay
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Ó Indian Academy of Sciences (0123456789().,-volV) (0123456789().,-volV)
RESEARCH NOTE
A de novo marker chromosome 15 in a child with isolated developmental delay MADHAVAN JEEVAN KUMAR1,2*, KALPANA GOWRISHANKAR2, VENKATASUBRAMANIAN HEMAGOWRI1,2 and JAYARAMA KADANDALE3 1Department
of Genetic Engineering, SRM Institute of Science and Technology, Kattankulathur 603 203, India of Medical Genetics, CHILDS Trust Medical Research Foundation (CTMRF), Kanchi Kamakoti CHILDS Trust Hospital, Chennai 600 034, India 3Department of Molecular Cytogenetics, Centre for Human Genetics, Bengaluru 560 100, India 2Department
*For correspondence. E-mail: [email protected]. Received 17 December 2019; revised 16 June 2020; accepted 17 June 2020 Abstract. We report a rare case of a 14-month-old male child who was referred for developmental delay. Clinical examination revealed a hypotonic infant with speech delay and no dysmorphic features. The banding cytogenetics revealed a small supernumerary marker chromosome. Upon silver staining, the marker showed the presence of satellite regions on either ends. Further, analysis using fluorescence in situ hybridization on marker chromosome revealed its origin from chromosome 15. Keywords.
cytogenetics; satellite chromosome; fluorescence in situ hybridization; marker chromosome; uniparental disomy.
Introduction
Materials and methods
Small supernumerary marker chromosome (sSMC) is a structurally abnormal chromosome fragment of unknown origin (ISCN 2013). In general, sSMC is unique in its size, and banding pattern and characterization of sSMC using routine banding cytogenetics is not achievable (Liehr et al. 2004). sSMC can either be present as part of 46 chromosomes or as additional material in a karyotype (Stefanou and Crocker 2004). Based on its structure, sSMC is categorized into five groups (i) satellite/bisatellited (ii) small metacentrics (iii) small supernumerary ring (iv) minutes and (v) neocentric chromosomes. sSMC can be routinely detected by various banding techniques like G-bands using trypsin digestion with Giemsa stain (GTG), reverse, constitutive heterochromatin and nucleolar organizer region (NOR) banding (Crolla et al. 1995). However, they can be best characterized by molecular techniques like fluorescence in situ hybridization (FISH), array comparative genomic hybridization (CGH), and uniparental disomy (UPD) studies. Hence, in the present study, we used banding cytogenetics, NOR staining and FISH to classify the sSMC detected in the patient’s sample.
Clinical report
A 14-month-old boy was referred to clinical genetic evaluation of developmental delay. The three generation pedigree analysis was not contributory. He was born after 40 weeks of uncomplicated gestation by normal vaginal delivery and is the first child from natural conception of nonconsanguineous parents. There is no history of antenatal problems, exposure to drugs or medical illness during pregnancy and there are also no perinatal issues. However, there is a history of speech delay (figure 1a). The proband was a
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