Genomic imprinting refers to an epigenetic phenomenon that leads to expression of certain genes in a parent-of-origin dependent manner. Altered gene imprinting has been associated with several well-described disorders, i.e., Beckwith–Wiedemann and Russell-Silver syndromes associated with chromosome 11p15 and Prader-Willi and Angelman syndromes associated with chromosome 15q11-q13 (Barlow and Bartolomei, 2014; Butler, 2009; Horsthemke and Buiting, 2008; Monk et al., 2019; Tucci et al., 2019). In humans, over 100 imprinting genes have been discovered in the past few decades (Baran et al., 2015; Court et al., 2014). There is increasing evidence that a variety of imprinting genes are highly expressed in the human placenta and play vital roles in embryogenesis (Hanna et al., 2016; Peters, 2014; Plasschaert and Bartolomei, 2014; Sanchez-Delgado et al., 2016; Smith et al., 2014; Tucci et al., 2019).
The molecular mechanisms underlying imprinting disorders include pathogenic genetic/epigenetic alterations of imprinted genes, copy number variants in the critical regions, and uniparental disomy (UPD)(Baran et al., 2015; Barlow and Bartolomei, 2014; Butler, 2009; Horsthemke and Buiting, 2008). Paternal and maternal UPD are frequently associated with clinically distinctive imprinting disorders. For instance, maternal UPD14 is associated with Temple syndrome (TS), whereas paternal UPD14 is associated with Kagami-Ogata syndrome (KOS)(Kagami et al., 2017; Ogata and Kagami, 2016; Prasasya et al., 2020). The common clinical features observed in patients with KOS and TS include feeding problems, short stature, growth retardation, hypotonia, developmental delay, intellectual disability, dysmorphic facial features, and kyphoscoliosis. Apart from the shared clinical features of these syndromes, oligohydramnios is present in the prenatal cases with TS while polyhydramnios occurs in the prenatal KOS cases. In addition, small bell-shaped thorax, cardiac defects, and abdominal wall defects are frequently observed in KOS but uncommon in TS (Ioannides et al., 2014; Kagami et al., 2015; Prasasya et al., 2020).
Interestingly, small supernumerary maker chromosomes (sSMCs) have been observed in a subset of cases with UPD. An sSMC is a structurally abnormal chromosome that is generally equal to or smaller than chromosome 20 in size and is generally unidentifiable by banding pattern alone. As the genomic content of sSMCs is variable, clinical phenotypes in patients with sSMCs are highly variable, ranging from clinically normal to severely affected (Liehr et al., 2011). To date, cases with either UPD or sSMC have been reported involving all of the autosomes and sex chromosomes; however, reports of cases with both UPD and sSMC are relatively rare(Liehr T. 2022). Liehr et al. (2011) reported 46 UPD + sSMC cases, among which, three cases involved maternal UPD14 + sSMC whereas only one case involved paternal UPD14 + sSMC (Liehr et al., 2011). To date, the vast majority of the patients with UPD14 and sSMC have been reported in association with TS resulting from maternal UPD14. Cases with paternal UPD14 and sSMC derived from chromosome 14 are rare.
In this study, we report a neonatal case with clinical features consistent with KOS. By utilizing cytogenetic and molecular techniques, we determined this patient is a carrier of both paternal UPD14 and an sSMC derived from chromosome 14. To our knowledge, this is the first case report of KOS resulting from paternal UPD14 and presence of sSMC with complex chromosomal rearrangement and no evidence of mosaicism.