To the best of my knowledge, hyperlexia is not a diagnosis in either the DSM or the ICD. I think you said it pretty well in your previous post, Jeri.

"Official" medical diagnoses are often normative and descriptive rather than, or at least as much as, etiological, and that is especially true of psychiatric diagnoses.

Diagnoses are labels, often necessary labels, but I often tell people to not get hung up on a label. It may more or less describe a configuration of signs, symptoms or experiences as reported by or observed in an individual, but a diagnostic label never, ever describes who a person is.