Among the congenital forms of hair dysplasia, tricorrhexis nodosa (TN) is very common and can be present in several pathologic conditions [
16‐
19]. TN is the most common defect in the hair shaft, leading to hair breakage [
20]. The primary abnormality is a focal loss of cuticles, causing fraying of the cortical fibers [
21,
22]. As emphasized by Landers
et al., TN may occur congenitally or can be acquired from chemical or physical trauma. Congenital TN has been associated with several syndromes including arginosuccinaciduria [
23], citrullinemia [
24,
25], Menkes syndrome [
26], Netherton disease [
27,
28], and syndromes associated with trichothiodystrophy hair shaft defect [
29]. SD patients have defective antibody responses despite normal serum immunoglobulin levels, and defective antigen-specific skin tests despite positive proliferative responses
in vitro. The cause of this functional immune deficiency and of this severe protracted diarrhea is unknown. The relationship between low birth weight, dysmorphism, severe diarrhea, hair shaft defect, immune deficiency and neonatal hemochromatosis-like liver disease is unclear. The coexistence of morphological, trichological and immunological abnormalities with early-onset intractable diarrhea disproportionate to the mucosal architectural abnormality (consistent with a primary enterocyte abnormality) suggests either mutations within several genes, inherited together by linkage disequilibrium, or, more probably, interference with a higher level of control, such as a patterning gene as seen in the Netherton syndrome which is an autosomal recessive congenital ichthyosis featuring chronic inflammation of the skin, hair anomalies, epidermal hyperplasia with an impaired epidermal barrier function, failure to thrive and atopic manifestations. The disease is caused by mutations in the
SPINK5 gene encoding the serine proteinase inhibitor lympho-epithelial Kazal-type inhibitor [
30,
31]. The characteristic hair abnormalities may allow a more focused search for candidate mutations, as relatively few genes have been implicated in hair development.