Managing Growth with IGF-1 Therapy

When a child is diagnosed with Laron syndrome, standard growth hormone therapy will not work because the body cannot “hear” the signal. Instead, for children who qualify, the standard of care is to bypass the broken growth hormone receptor and provide the missing end-product directly. This is done using Mecasermin (brand name Increlex), which is a recombinant human IGF-1 ^[1]. Note that this medication is for specialist-directed treatment of severe primary IGF-1 deficiency; it is not appropriate for everyone, and eligibility must be checked by an endocrinologist.

Bypassing the “Broken Lock”

As discussed in previous sections, growth hormone is the “key” that normally opens the “lock” (receptor) to produce IGF-1. In Laron syndrome, because that lock is broken, the body never makes enough IGF-1 on its own ^[2]. Mecasermin acts as a direct replacement for that missing IGF-1 ^[1]. By giving this hormone through an injection, we provide the body with the specific tool it needs to make bones and tissues grow ^[3].

The Treatment Regimen

Mecasermin is typically administered as a subcutaneous (under the skin) injection twice a day ^[4].

• Starting Dose: While some clinical cohorts report a starting dose of 40 micrograms per kilogram (mcg/kg) given twice daily ^[4], the specific starting range must be determined by your doctor. You must only use the dose prescribed by your physician and never adjust it yourself.
• Titration: If your child tolerates the initial dose well, your doctor will slowly increase or titrate the dose under careful supervision. In some clinical settings, the dose may be increased up to a maximum of 120 mcg/kg twice daily, but this relies entirely on individualized medical guidance ^[4].
• Coordination with Food: This is perhaps the most critical part of the daily routine. Because IGF-1 has insulin-like effects, it can cause blood sugar to drop. Mecasermin must be given shortly before or after a meal or snack, or exactly as specified by your local product label ^[5]. If your child cannot eat for any reason, the dose should be skipped to prevent dangerous drops in blood sugar ^[5].
• Contraindications: Mecasermin must not be used if your child has closed growth plates, an active or suspected malignancy, or a hypersensitivity to the drug.

Realistic Growth Expectations

It is important to have a clear understanding of what treatment can—and cannot—achieve. While Mecasermin significantly improves growth, it often does not result in a “typical” adult height.

• Growth Velocity: Before treatment, a child with Laron syndrome may grow only about 3.4 cm (about 1.3 inches) per year. In the first year of treatment, this often jumps to about 6.5 to 7.3 cm per year ^[6][4].
• Height Gains: Over the course of treatment, children typically see an improvement in their Standard Deviation Score (SDS)—a measure of how their height compares to peers. The average gain is about 0.9 to 1.4 points on this scale ^[7].
• Adult Height: In a large registry of patients, about 10.5% of those with Laron syndrome reached a near-adult height within the general population reference range ^[7]. While many remain shorter than average, the treatment provides growth that can improve daily functioning ^[4].

The Importance of Timing

When it comes to treatment, earlier is almost always better.

• Prepubertal Advantage: The best growth responses are seen in children who are treatment-naïve (have not had prior growth treatments) and are prepubertal (have not yet started puberty) ^[7][8].
• Reaching the Target: In one subgroup analysis of that registry, nearly half (about 50%) of the specific children who started treatment while they were young and prepubertal reached a near-adult height in the normal range ^[7].
• Why Start Early?: Starting early gives the bones more time to grow before the growth plates naturally close at the end of puberty ^[9]. Once those plates close, no further height can be gained, regardless of the treatment used ^[10].

Your medical team will monitor your child’s height, weight, and bone age (using X-rays of the hand) to ensure the dose is optimized for their specific stage of development ^[10][11].