How many people are diagnosed with harlequin type ichthyosis each year?

Harlequin type ichthyosis is an extremely rare genetic skin disorder, with an estimated incidence of about 1 in 300,000 to 1 in 500,000 live births. This means that only a handful of cases are diagnosed each year worldwide, often fewer than 20. Due to its rarity, precise annual statistics can vary, but it remains one of the least common forms of ichthyosis.