Mutations in the HOXA13 gene cause hand-foot-genital syndrome. Which developmental principle does this best illustrate?

• A Anterior prevalence — HOXA13 specifies proximal limb segments
• B Posterior prevalence — more posteriorly expressed HOX genes suppress anterior HOX gene function ✓
• C HOXA13 is expressed in the zone of polarising activity (ZPA) to pattern the thumb
• D HOXA13 regulates apical ectodermal ridge (AER) maintenance

Explanation

HOX genes follow posterior prevalence (posterior dominance): genes expressed more posteriorly or distally along the body/limb axis suppress the activity of more anteriorly expressed paralogue members. HOXA13, a 5′ (posterior/distal) gene, specifies distal limb (hand/foot) and urogenital sinus identity; loss-of-function reveals its dominant suppression of proximal-specifying paralogues, resulting in digit and uterine anomalies. The AER maintains the proximo-distal limb growth axis via FGF signals and is regulated by Wnt/BMP, not directly by HOXA13. The ZPA patterns the anterior-posterior (thumb-to-little finger) axis via SHH.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.