Design: Systematic review and random-effects meta-analysis of prevalence studies
Population: 50 studies of people with neurofibromatosis type 1, with genotype subgroups where reported
Primary outcome: Prevalence of intellectual disability, autism spectrum disorder, ADHD, seizures, epilepsy, depression and anxiety
Effect: ADHD 33% (95% CI 26–40); seizures 11% (8–14); epilepsy 9% (6–11); intellectual disability 8% (6–11) overall but 41% (29–52) with microdeletion

Fifty studies were pooled to settle prevalence estimates in neurofibromatosis type 1 that have varied widely across the literature. Attention deficit hyperactivity disorder was the commonest finding at 33% (95% CI 26–40, 29 studies). Intellectual disability was 8% (6–11), autism spectrum disorder 11% (7–14), seizures 11% (8–14) and epilepsy 9% (6–11). Depression was 13% (3–23) and anxiety 12% (5–20).

The genotype split is the part worth remembering. In the small number of studies reporting NF1 microdeletions separately, intellectual disability was 41% (29–52) and ADHD 45% (25–65) — five times and rather more than the general NF1 figures. Both estimates rest on two studies each, so the intervals are wide and the point estimates should be held loosely, but the direction is consistent with what is known about contiguous gene deletion.

None of this is a new recommendation: neuropsychiatric screening in NF1 is already advised. What the numbers do is make the case concrete. A one-in-three chance of ADHD is not a rare complication to look out for; it is a near-default part of the condition, and a clinic that sees NF1 without a route to neuropsychological assessment is missing most of them.

Screen every child with NF1 for ADHD and learning difficulty — do not wait for a school referral.
Where a microdeletion genotype is known, expect a substantially higher likelihood of intellectual disability and plan educational support early.
Ask about mood and anxiety at review; both run at over one in ten and are easily missed against the visible features.
Establish a referral route to neuropsychology as part of the NF1 clinic, rather than case by case.
Depression and anxiety prevalence estimates had very wide intervals (3–23% and 5–20%), so treat those as approximate.

Why it matters

Screening advice that exists on paper gets followed when the clinician knows the number behind it.

The statistics, in plain English

Prevalence meta-analyses pool proportions from studies with different ascertainment, so a clinic-based series will report more than a population one — that is a large part of why published estimates have varied. The microdeletion figures come from two studies each, which is why the intervals span 29–52% and 25–65%; they are a signal that the subgroup differs, not a usable prevalence.