Clinical Features of a Japanese Girl With Radio-Tartaglia Syndrome due to a SPEN Truncating Variant.

Radio-Tartaglia syndrome (RATARS) (MIM#619312) is a genetic disorder caused by heterozygous truncating variants of SPEN on chromosome 1p36. This syndrome is extremely rare, with only 34 cases reported to date. RATARS is characterized by developmental delay, hypotonia, and intellectual disability. In this study, we report a Japanese girl with psychomotor delay, hypotonia, and facial features resembling Down syndrome (DS). We identified a de novo heterozygous pathogenic variant of SPEN and diagnosed her with RATARS. The patient was born at 38 weeks and 1 day of gestational age, weighing 2598 g, without respiratory or feeding difficulties. We first considered DS as a differential diagnosis based on the developmental delay with hypotonia and facial features, including an upslanted palpebral fissure, hypertelorism, epicanthus folds, and a low nose; however, it was ruled out after cytogenetic testing. Microarray analysis revealed no pathogenic aberrations. We performed trio-based whole exome sequencing and identified a recurrent pathogenic variant of SPEN:NM_015001.3:c.6223_6227del, p.(Ser2075GlufsTer46). Although some features of RATARS have been reported to be similar to those of 1p36 deletion syndrome, facial similarity to DS was a characteristic of our case. Whether this feature is unique to the patient or relatively common in individuals with RATARS should be discussed further as more cases of individuals with RATARS are reported.