A Rare Genetic Disorder: Partial Trisomy on Chromosome 21

A 7-year and 7-month-old boy presented with pubic hair. He was born at the 35th gestational week with a birth weight of 2400 g. He was diagnosed with Down syndrome (DS) in another center. Despite normal motor and mental development, he was under a special education in school since he was labeled with DS. Physical examination revealed dysmorphic findings, such as up-slanting palpebral fissures, epicanthus, low-set ears, and low nasal bridge, all suggesting DS. The height was 136 cm [>97th percentile, >2.7 standard deviation score (SDS)] and the weight was 31.6 kg (between 90 and 97th percentile, 2.7 SDS). Axillary hair was absent, while pubic hair appeared as stage 2 according to Tanner staging. Left testis was 2 mL and right testis was 1 mL. Complete blood count was normal, electrolytes were in normal ranges, 17-hydroxy progesterone (17-OHP) was 0.64 mg/mL, dehydroepiandrosterone sulfate was 191 µg/dL, and early morning cortisol level was 9.8 µg/dL. The bone age was 10 years. Echocardiography was normal. The patient was diagnosed with premature adrenarche. Despite the presence of typical appearance of Down syndrome, the patient had a significant tall stature. Repeated karyotype analyses revealed 47,XY,+2 (q22.11-qter), while Array CGH detected an increase of 10578411 base between 36103774 and 46682184 bases of the q22.11 and q22.3 bands of chromosome 21. Gene and gene regions which constitute the phenotypic features of DS are known to be located on the distal parts of the long arm of chromosome 21. The detected duplication in our patient was located on the distal part of the long arm of chromosome 21. This might be the reason of dysmorphic facial features. This case of partial trisomy of chromosome 21 was reported because of its scarcity.