Is there any evidence of an excess of IGF-1 facilitating in the...

Is there any evidence of an excess of IGF-1 facilitating in the development of autism or is this discussion purely hypothetical at this point?

It is clearly stated at the top of the paper (which I linked in the original post) that this is a hypothesis. Further, the paper is titled The Possible Role of Postnatal Biphasic Dysregulation of IGF-1 Tone in the Etiology of Idiopathic Autism Spectrum Disorder.

But if you read the paper, it is also clear that the author hasn’t just expanded on a thought bubble.

He supports his hypothesis with evidence previously reported by other researchers.

He states that several growth and developmental deviations have been described to precede or correlate with later ASD diagnosis.

He notes that accelerated very early growth in children with autism has been demonstrated for:

• body length [47,48],
• total brain volume [25,49,50,51],
• cortical surface area [52],
• excess extra-axial fluid volume [53]

He also provides evidence that, following a period of overgrowth in toddlers, a slowing or even arrested growth has been reported for many of these parameters in early childhood [51,52,54,55].

He adds that a biphasic developmental trajectory has also been found for brain structural connectivity [56].

He refers to two longitudinal imaging studies which compared at-risk infants later diagnosed with ASD to non-affected peers [57] or diagnosed toddlers to typical controls [58]. These studies reported structural hyperconnectivity between brain regions at earlier scans, in contrast to hypoconnectivity at the later time points (24- ca. 36 months, depending on the study).

Finally, in studies of head circumference, early overgrowth in ASD (and in pervasive developmental disorder not otherwise specified, in earlier studies) was found, which was absent when compared with children with ADHD [59,60] or generalized or other developmental delays [48,61].

All of this perhaps still doesn’t exactly answer your question as to whether IGF-1 plays a role in this process. Could perhaps other growth factors be responsible?

In this 2022 paper, Swedish researchers investigated the link between growth factors and preterm brain volumes at term. The researchers found that

IGF-1 levels were independently positively associated with the total brain (p < 0.001, β = 0.90), white matter (p = 0.007, β = 0.33), cortical gray matter (p = 0.002, β = 0.43), deep gray matter (p = 0.008, β = 0.05), and cerebellar (p = 0.006, β = 0.08) volume adjusted for GA at birth and postmenstrual age at MRI. No associations were seen for other growth factors.

These researchers concluded that

Optimizing levels of IGF-1 might improve brain growth in extremely preterm infants.

Add this to the list as another potential use for NNZ-2591….