A 10-month-old boy was admitted with a 4-month history of progressive macroglossia, coarse facial features and loss of motor skills (figure 1).

Infant with macroglossia.

What is the most likely diagnosis?

Beckwith Wiedemann syndrome (BWS).

Hypothyroidism.

Glycogen storage disorder.

Mosaic Down syndrome.

Mucopolysaccharidosis (MPS).

A detailed history revealed a 6-month history of constipation and dry skin. While he had not yet started walking, he had demonstrated progressive fatigability and a loss of motor skills. The antenatal history and delivery were uneventful; the neonatal screening was normal. Physical examination revealed a pale child with dry skin, coarse facial features, macroglossia and myxoedema (figure 1). His thyroid gland was not palpable. The child’s weight was on the 91st centile, length was between the 9th and 25th centiles and head circumference was on the 46th centile, respectively.

The UK newborn screening …