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Autosomal recessive isolated familial acanthosis nigricans in a Pakistani family due to a homozygous mutation in the insulin receptor gene

MADAM, Acanthosis nigricans (AN) is characterized by noninflamed, thick, brown-black pigmentation of the epidermis of the neck, dorsal hands and feet, axilla, umbilicus, knees and elbows. It has been reported in both inherited as well as acquired forms (e.g. as a paraneoplastic syndrome). Most cases of AN have been described in association with insulin resistance syndromes and fibroblast growth factor receptor (FGFR) mutations. However, it also occurs as a symptom of diverse syndromes, including leprechaunism, Rabson–Mendenhall syndrome and thanatophoric dysplasia. The prevalence of isolated familial acanthosis nigricans (IFAN) is not known; however, to date, five families with autosomal dominant IFAN have been reported. Here, we report a consanguineous multigenerational Pakistani family (Fig. 1a) with IFAN following an autosomal recessive inheritance pattern. All individuals of the family were born with normal skin. At the age of about 5 years, the parents of three children (IV:3, IV:5 and IV:6; Fig. 1a) reported dark rings of ‘dirt’ that they had been unable to remove from the skin and which they considered dirty or difficult-to-clean skin. Dermatological examination showed rugosity, thickening and brown-black pigmentation of the epidermis of the neck, dorsal hands and feet, axilla, knees and elbows, as well as of the epidermis surrounding the umbilicus (Fig. 1b). Clinical examination confirmed these to be areas of AN in all affected individuals. Several small, warty acanthomas were also noted on the upper trunk, the axillae and the groin (Fig. 1b, ii, iii). The skin changes became more prominent with age. The