Don't tease him just because he can't write his name.
Literal
Name [subject-が] can-not-write [because-からといって] he [object-を] tease prohibitive-[てはいけない].
~からといって = 'just because X, (don't assume Y).' The pattern explicitly tags a reason as insufficient to justify a conclusion — a hedge against lazy inference. Common in moral or reasoned statements. 書ける is potential form with が for the subject of potential.