A number sign (#) is used with this entry because of evidence that autosomal recessive keratitis-ichthyosis-deafness syndrome (KIDAR) is caused by homozygous or compound heterozygous mutation in the AP1B1 gene (600157) on chromosome 22q12.

Autosomal recessive keratitis-ichthyosis-deafness syndrome (KIDAR) is characterized by neonatal-onset ichthyotic erythroderma and profound sensorineural deafness, with failure to thrive and developmental delay in childhood. Severe corneal scarring with vision loss has been observed in adulthood. Low plasma copper and ceruloplasmin levels have been reported in some patients (Alsaif et al., 2019; Boyden et al., 2019).

An autosomal dominant form of KID syndrome (KIDAD; 148210) is caused by mutation in the GJB2 gene (121011) on chromosome 13q12.

Mutation in the AP1S1 gene (603531) causes a disorder with overlapping features (MEDNIK; 609313).

Desmons et al. (1971) described 3 sibs, born of first-cousin parents, with congenital ichthyosiform erythroderma and profound sensorineural deafness. The oldest sib had bilateral ectropion, but corneal lesions were not reported. All exhibited hyperlordosis and swollen abdomens in early childhood, with delayed growth. At examination in middle age, all 3 sibs showed hepatomegaly, hepatic cirrhosis, and glycogen storage.

Cremers et al. (1977) studied an 18-year-old woman who developed ichthyosiform erythroderma in the neonatal period. Deafness was diagnosed at age 4 years, and she experienced photophobia and chronic blepharoconjunctivitis at age 11, at which time slight corneal defects were detected on fluorescein staining and pannus of the cornea was observed. At age 18 years, her nails were thick with subungual keratosis, scalp hair was brittle, eyebrows and eyelashes were sparse, and axillary and pubic hair was absent. She had anhidrosis, and dental development was incomplete, with small misshapen teeth. Both corneas showed a pannus. Intelligence was normal by psychologic testing. The authors noted 8 similar cases that had been reported in the literature.

Wilson et al. (1991) reported an 18.5-year-old woman with ichthyosiform erythroderma from infancy in whom sensorineural deafness was recognized at age 3 years and keratoconus with myopia and photophobia were noted at age 12 years. She had coarse hair, pannus of the cornea, and broad tongue with large anterior papillae. Neurologic examination was normal except for low IQ of about 60. She underwent menarche at age 15 and developed metrorrhagia with coagulopathy, which prompted hepatic evaluation. Laboratory data were consistent with hypersplenism and chronic liver disease, with slightly elevated serum copper. CT scan revealed esophageal varices, atrophic right hepatic lobe with enlargement of the left lobe, and splenomegaly. Liver biopsy showed green nodular tissue, with micronodular cirrhosis obliterating the normal hepatic architecture on light microscopy. She had progressive liver failure and eventually underwent liver transplantation; abundant copper was demonstrated in the hepatectomy specimen.

Jurecka et al. (1985) described a 7-year-old Yugoslavian girl who had erythrokeratoderma-like ichthyotic skin from birth, profound sensorineural deafness diagnosed at 12 months of age, and vascularizing keratitis that developed by age 2 years. She also exhibited hypohidrosis, nail dystrophy, and scarring alopecia. Head CT scan showed markedly enlarged cisterna magna with cerebellar atrophy, and the patient's IQ was 80. Punch biopsies of affected skin showed 'basket-weave' hyperkeratosis, acanthosis, and papillomatosis, with follicular plugging of the epidermis and mild nonspecific inflammatory perivascular infiltrate. Staining revealed a high amount of glycogen in smooth muscle and vessel walls; electron microscopy showed excess glycogen diffusely accumulated within the cytoplasm of dermal cells, including smooth muscle and vessel walls, perineural cells, Schwann cells, axons, and connective tissue cells.

Alsaif et al. (2019) studied a 4.3-year-old girl and her 1.5-year-old brother (patients 1 and 2), born of consanguineous parents of Pakistani origin, and an unrelated 4.5-year-old boy (patient 3), born of consanguineous parents of Saudi origin, with ichthyosis, erythroderma, profound deafness, sparse hair, and global developmental delay, who were homozygous for mutations in the AP1B1 gene. All showed failure to thrive in early childhood, and the 2 sibs had enteropathy requiring gastrostomy tube feedings. All 3 had low plasma copper and ceruloplasmin levels, and the 2 sibs had hepatopathy, with hepatomegaly in the brother; however, there was no increased copper content in the liver. Other features included bilateral ectropion in patient 2 and palmoplantar keratoderma in patient 3, and the 2 older children were reported to have impaired intellectual development.

Boyden et al. (2019) described a 33-year-old man (patient 424) and an unrelated 11-month-old girl (patient 1325) with ichthyotic erythroderma, deafness, and photophobia, as well as failure to thrive and developmental delay. The man also exhibited ectropion with corneal scarring resulting in nearly complete vision loss in adulthood, as well as anhidrosis, fissured tongue, gingival destruction, and tooth loss. Both patients had mild palmoplantar keratoderma. Skin histology from patient 1325 showed focal separation of keratinocytes above the basal layer and compact hyperkeratosis, with abnormally high numbers of basophilic vesicles within the proliferative layers of the epidermis; transmission electron microscopy in patient 424 confirmed large intracytoplasmic vacuoles. Staining of patient keratinocytes for various protein markers showed abnormal epidermal differentiation and hyperproliferation, as well as mislocalization of intercellular junction proteins.

Vornweg et al. (2021) reported a 2.5-year-old German girl with KIDAR and mutation in the AP1B1 gene. At 2 weeks of age, she developed an ichthyosiform erythroderma and chronic severe pruritus. Global developmental retardation and failure to thrive were observed, as well as partial alopecia, bilateral ectropion, and thickened plantar surfaces. Blood counts were normal, as were serum levels of very long chain fatty acids (VLCFA), iron, zinc, copper, and ceruloplasmin. She had chronic diarrhea but showed improved growth parameters by age 2.5 years. She was also diagnosed with bilateral deafness and had developed photophobia. The authors noted similarities to previously described patients with AP1B1 mutations, including compensation in later childhood for the severe failure to thrive and developmental delays observed in the first months of life.

Ito et al. (2021) studied a 2-year-old Japanese boy who had ichthyosis, developmental delay, and deafness, and mutation in the AP1B1 gene. He was born with papules and moderate hyperkeratosis in erythrodermic skin over almost the entire body. Hair was normal. He had hearing loss as well as moderate mental and motor retardation, with inability to hold up his head at 5 months of age. He also had enteritis, intussusception, and recurrent infections. Laboratory analysis showed low serum calcium and very high alkaline phosphatase, as well as low serum copper and ceruloplasmin levels.

Faghihi et al. (2022) reported a 6.5-year-old Iranian boy who had developmental delay, keratitis, ichthyosis, and hearing loss, and mutation in the AP1B1 gene. He had failure to thrive, and motor milestones were delayed by 6 to 12 months. He had a history of recurrent mastoiditis, sinusitis, and otitis media, and imaging showed subtotal obliteration of mastoid air cells. Auditory examination revealed complete sensorineural deafness, and he had cystic and dysplastic changes of the cochlea suggestive of Mondini dysplasia, with mild dilation of the vestibular aqueduct. He was nonverbal, but this was attributed to his profound hearing loss. Other features included palmoplantar keratoderma, ichthyosis with white scaly skin and erythroderma, and sparse hair and eyebrows. He also had keratitis associated with photophobia, erythema, pain, and corneal scarring. Brain MRI showed mild thinning of the corpus callosum, suggesting low-grade hypoplasia. Laboratory analysis showed persistent high levels of transaminases and alkaline phosphatase, and low plasma copper and ceruloplasmin.

Clinical Variability

Meric et al. (2021) described a 7-year-old Turkish girl who had ichthyosis, developmental delay, hearing loss, photophobia, high myopia, hepatomegaly, and chronic diarrhea, and mutation in the AP1B1 gene. Examination revealed mild intellectual disability; generalized ichthyosis, erythrodermia, and hyperkeratosis; and partial alopecia with sparse hair and eyebrows. She also exhibited features not previously reported in patients with AP1B1 or AP1S1 mutations, including severe short stature with growth hormone (GH1; 139250) deficiency and hypothyroidism. Electromyography performed to investigate peripheral neuropathy was normal, and serum transaminases, copper, ceruloplasmin, zinc, and VLCFA levels were normal.

The transmission pattern of KID syndrome in the family reported by Desmons et al. (1971) was consistent with autosomal recessive inheritance.

In 2 sibs of Pakistani origin (patients 1 and 2) and an unrelated Saudi boy (patient 3) with ichthyotic erythroderma and deafness, Alsaif et al. (2019) identified homozygosity for a microdeletion (600157.0001) and a splicing mutation (600157.0002), respectively, in the AP1B1 gene. Their unaffected parents were heterozygous for the mutations. All 3 patients had low plasma copper and ceruloplasmin levels, and the authors noted overlap between the phenotype of these patients and that of MEDNIK syndrome (609313), which is associated with abnormal copper metabolism; however, the patients of Alsaif et al. (2019) did not have neuropathy and did not show copper toxicity or accumulation.

From a large cohort of individuals with keratinization disorders with or without associated syndromic features, Boyden et al. (2019) identified 2 unrelated patients with ichthyotic erythroderma, deafness, and photophobia who had biallelic mutations in the AP1B1 gene: a 33-year-old man (patient 424) who was compound heterozygous for a missense mutation (C144R; 600157.0003) and a 1-bp deletion (600157.0004), and an 11-month-old Ashkenazi Jewish girl (patient 1325) who was homozygous for a nonsense mutation (E792X; 600157.0005). Both patients also exhibited palmoplantar keratoderma, and the older patient developed corneal scarring causing nearly complete vision loss in adulthood.

In a 7-year-old Turkish girl with ichthyosis, developmental delay, and deafness, Meric et al. (2021) performed whole-exome sequencing (WES) and identified homozygosity for a missense mutation in the AP1B1 gene (L223P; 600157.0006). Sanger sequencing confirmed the mutation, and her unaffected first-cousin parents were heterozygous for the variant.

By whole-exome and Sanger sequencing in a 2.5-year-old German girl with KIDAR syndrome, Vornweg et al. (2021) identified compound heterozygosity for a previously reported 1-bp deletion (600157.0004) and a missense mutation (R108W; 600157.0007) in the AP1B1 gene. Her healthy nonconsanguineous parents were each heterozygous for 1 of the variants.

By WES in a 2-year-old Japanese boy with ichthyosis, developmental delay, and deafness, Ito et al. (2021) identified compound heterozygosity for nonsense mutations in the AP1B1 gene, Q618X (600157.0008) and Q866X (600157.0009). Sanger sequencing confirmed heterozygosity for 1 of the variants in each of his unaffected parents.

By WES in a 6.5-year-old Iranian boy with KIDAR, Faghihi et al. (2022) identified homozygosity for a nonsense mutation in the AP1B1 gene (Y421X; 600157.0010). Sanger sequencing confirmed that his first-cousin unaffected parents were heterozygous for the mutation, which was not found in public variant databases.