Editor—Tetrasomy 21 without mosaicism has previously been described in four liveborn children, two of whom had physical features consistent with Down syndrome. We describe a male infant with partial tetrasomy 21 whose examination was consistent with but not typical of trisomy 21.

The clinical features of the proband are summarised in table 1. The proband was the second child born to healthy white parents. Their first child was a normal son aged 18 months. There was no significant family history and no consanguinity. The mother was 34 years old at the time of the birth and the father was 33 years old.

During the pregnancy poor weight gain was reported, although the mother stated that the fetal movements were normal. A detailed ultrasound scan at 18 weeks of gestation was normal. A repeat scan at 30 weeks of gestation showed intrauterine growth retardation.

Labour occurred spontaneously at 33 weeks of gestation and an emergency caesarian section was performed for fetal distress and growth retardation. The birth weight was 1420 g (3rd centile), length 38 cm (1.8 cm less than the 3rd centile), and head circumference 27 cm (0.4th centile). The proband required special care because of his prematurity and small size. Hypospadias, a bifid scrotum, and microcephaly were noted and blood was sent for chromosome analysis on the second day of life (see below). The proband was tube fed for the first 4 weeks of life because of nasal regurgitation and difficulty coordinating sucking and breathing. There were no reports of neonatal hypotonia. A small umbilical hernia was noticed at 1 week of age. He was discharged at 6 weeks of age feeding well with a weight of 2000 g (200 g less than 0.4th centile).

On examination at …