Mosaic and partial monosomy of chromosome 21 in a case with low platelets count

Monosomy is defined as the presence of only one chromosome instead of two in humans. Partial monosomy occurs when only a portion of the chromosome is present in a single copy, while the rest has two copies. It can occur in unbalanced translocations or deletions.

In this report, a 6 years old girl was presented who was referred to the Pediatric Dep, Shahid Sadoughi Hospital,Yazd, Iran, due to multiple congenital anomalies such as: frontal bossing, horizontal palpebral fissure, small deepest eyes, aplastic nasal bridge, broad philtrum, low set ears, large prominent ears, short neck, microcephaly, pectus excavatum, mental retardation, and dislocation of the hip. In peripheral blood smear, platelets were decreased but other hematological levels were normal. The karyotype result indicated a mosaic monosomy and partial monosomy of chromosome 21.

According to this and other case reports of monosomy of chromosome 21, this disease had very low prevalence rate among live infants or children. The present case had some congenital anomalies that present with abnormal medical condition. Therefore these patients must be evaluated for chromosomal studies.