A child with nail changes

An otherwise healthy 3 year old boy presented with a 3 week history of painless nail alterations, which were noticed by his mother, with incidental findings of nail discoloration and brittle nails with cracks. All the nail changes moved distally with nail growth. Physical examination found proximal nail plate separation from the nail matrix on the right thumbnail and left index fingernail, one white transverse furrow in the right third fingernail, and one transverse whitish, non-palpable, non-blanching line on the right fourth fingernail (fig 1). No toenails were involved. The child was usually well, however had seen a doctor for hand, foot, and mouth disease five weeks before the nail presentations.

What are the nail changes shown in figure 1, and what are the possible causes in this child?