Tetrasomy 21pter‐q22.11: molecular, cytogenetic, and clinical findings

Partial tetrasomy 21 in a male infant

“…Findings in previously reported cases of both mosaic and non-mosaic tetrasomy 21 include a flat occiput,10 (our patient) a high, broad forehead,12 18 (our patient), hypertelorism or telecanthus,12 (our patient), and a short and anteverted nose13 (our patient). Our patient also had a carp shaped mouth.…”

“…Our patient also had a carp shaped mouth. Non-specific genitourinary anomalies were more frequent (table 4), and cryptorchidism,11 12 hypospadias, and a small scrotum (our patient) and a large penis13 have been reported. A patent ductus arteriosus was described in one premature infant,11 but no other case had a cardiac abnormality.…”

“…The authors concluded that the child had some but not all of the features of Down syndrome and that genes outside the Down syndrome critical region (DCR) were influential in the trisomy 21 phenotype 12. Tetrasomy 21 was also described in an 11 year old male with psychomotor and speech retardation (but with normal growth), brachycephaly, a prominent lower lip, macrogenitalism, and idiopathic precocious puberty 13. The Jackson score for this child was not consistent with Down syndrome 13…”

“…However, there was considerable variation in both growth and development and one girl with non-mosaic tetrasomy 21 walked independently at the age of 18 months and had single words at the age of 33 months 10. A child with normal growth parameters13 and a child with normal height and weight but with microcephaly have also been reported 10…”

Tetrasomy 21pter->q21.2 in a male infant without typical Down's syndrome dysmorphic features but moderate mental retardation

“…To our knowledge, complete or partial tetrasomy 21 without mosaicism has been reported in only five liveborn infants. [4][5][6][7][8] Four of these five infants showed classical dysmorphic signs of Down's syndrome 4-6 8 (table 1). In the case described by Cerretini et al, 7 the child showed only one (brachycephaly) of the ten most discriminating features of Down's syndrome, 9 suggesting that partial tetrasomy 21 does not consistently produce a Down's syndrome phenotype.…”