An unusual Case of Segmental Hailey-Hailey Disease Developing in a 1.5-Year-Old Child: A Proposed Diagnosis.

Sir,

When I read the title chosen by Singh and Tripathy: “A rare case of childhood-onset Hailey–Hailey disease at an unusual site”,[1] I had a particular suspicion. And when I opened the article, my assumed diagnosis was confirmed. The disorder represents a classical example of a specific mosaic form of Hailey-Hailey disease.

Molecular analysis would have shown that the child is heterozygous for the HTP2C1 mutation in all cells of his body, whereas the unilateral linear lesion would reveal loss of heterozygosity resulting in loss of the corresponding wild-type allele.[2] This mutational event must have occurred at an early developmental stage, within the first week after fertilization. Hence, my diagnosis is superimposed mosaicism in Hailey-Hailey disease. (“Superimposed mosaicism” is a recently introduced term for what has previously been called “type 2 segmental mosaicism”.[23]) In addition, the boy will almost certainly develop, later in life, the classical non-segmental involvement of the disorder.

In the past, superimposed linear Hailey-Hailey disease has erroneously been taken as a distinct disorder called “relapsing linear acantholytic dermatosis”.[45] In one of these cases,[4] examination of the patient's mother revealed the classical non-segmental involvement of Hailey-Hailey disease, and the patient herself did also develop non-segmental lesions at 24 years of age.[2]

Finally, I hope that the authors have meticulously interrogated and physically examined the parents of this boy. For obvious reasons, it would not be sufficient to hear from the parents that “such skin disorder” has never occurred in the family.

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Conflicts of interest

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