Ichthyosis follicularis, atrichia and photophobia (IFAP) and hereditary mucoepithelial dysplasia: Two syndromes that share a common clinical spectrum

Ichthyosis follicularis, atrichia and photophobia syndrome (IFAP) is an X-linked inherited disease caused by pathogenic variants in the gene encoding the membrane-bound transcription factor peptidase, site 2 (MBTPS2). Clinical presentation includes ichthyosis follicularis, alopecia, photophobia and developmental delay. Hereditary mucoepithelial dysplasia (HMD) is a dominantly inherited disease characterized by keratitis, non-scarring alopecia, skin lesions including follicular keratosis, perineal erythema, and mucosal involvement. Recently, variants in SREBF1, a gene coding for a transcription factor related to cholesterol and fatty acid synthesis, have been associated with the disease. These two syndromes share a common clinical spectrum. Here, we describe an IFAP syndrome patient with a novel variant in the MBTPS2 gene and an HMD patient with a previously reported variant in the SREBF1 gene. In addition, we present a review of the literature describing the triad characterized by non-scarring alopecia, keratosis follicularis, and ocular symptoms common in both IFAP and HMD patients to raise awareness of these underdiagnosed diseases. We also highlight the subtle differences in clinical presentation between the two disorders to better enable differentiation.

A novel mutation in MBTPS2 causes ichthyosis follicularis, alopecia, and photophobia syndrome

Background

The ichthyosis follicularis, alopecia, and photophobia (IFAP) syndrome is a rare X‐linked genodermatosis characterized by noninflammatory spiny follicular hyperkeratosis, severe photophobia, and non‐scarring alopecia with variable severities. IFAP syndrome results from mutations in the gene encoding the membrane‐bound transcription factor peptidase, site 2 (MBTPS2).

Methods

We present an 11‐year‐old male with typical clinical features of IFAP syndrome, including diffuse follicular hyperkeratosis, alopecia, photophobia, psoriasiform plaques, short statue, nail dystrophy, mental retardation, and seizures.

Results

A novel missense mutation (NM_015884.4: c.1298T > C; NP_056968.1: p. L433P) in the membrane‐bound transcription factor peptidase, site 2 gene (MBTPS2) was identified in our patient. The heterozygous MBTPS2 mutation was identified in his mother but not his father.

Conclusion

This study demonstrated a novel MBTPS2 mutation in a patient with IFAP syndrome and thus expands the known MBPTS2 molecular repertoire.

Novel MBTPS2 missense mutation causes a keratosis follicularis spinulosa decalvans phenotype: mutation update and review of the literature

Keratosis follicularis spinulosa decalvans (KFSD) is an X-linked condition characterized by keratotic follicular papules and progressive alopecia, which is caused by mutations in the MBTPS2 gene. We carried out a genetic study on a child who was suspected clinically to have KFSD. Sanger sequencing was performed to detect mutations in the entire coding region of MBTPS2. A novel missense mutation (c.599C>T) was identified in the patient, confirming a diagnosis of KFSD. We reviewed related cases with MBTPS2 mutations for evidence of genotype-phenotype correlations.

Golgi post-translational modifications and associated diseases

For non specialists, Golgi is a very well known subcellular compartment involved in secretion and correct targeting of soluble and transmembrane proteins. Nevertheless, Golgi is also specifically involved in many different and diverse post-translational modifications. Through its diverse functions, Golgi is not only able to modify secreted and transmembrane proteins but also cytoplasmic proteins. The Golgi apparatus research field is so broad that an exhaustive review of this organelle is not doable here. The goal of this review is to cover the main post-translational modifications occurring at the Golgi level and present the identified associated diseases.

Discovery in genetic skin disease: the impact of high throughput genetic technologies

The last decade has seen considerable advances in our understanding of the genetic basis of skin disease, as a consequence of high throughput sequencing technologies including next generation sequencing and whole exome sequencing. We have now determined the genes underlying several monogenic diseases, such as harlequin ichthyosis, Olmsted syndrome, and exfoliative ichthyosis, which have provided unique insights into the structure and function of the skin. In addition, through genome wide association studies we now have an understanding of how low penetrance variants contribute to inflammatory skin diseases such as psoriasis vulgaris and atopic dermatitis, and how they contribute to underlying pathophysiological disease processes. In this review we discuss strategies used to unravel the genes underlying both monogenic and complex trait skin diseases in the last 10 years and the implications on mechanistic studies, diagnostics, and therapeutics.

Novel MBTPS2 missense mutation in the N-terminus transmembrane domain in a patient with ichthyosis follicularis, alopecia, and photophobia syndrome

Ichthyosis follicularis, alopecia, and photophobia (IFAP) syndrome is an X-linked dominant condition characterized by the triad of ichthyosis follicularis, alopecia, and photophobia caused by mutations in the MBTPS2 gene. Herein we describe a proband with IFAP syndrome with mild cutaneous manifestations and a novel MBTPS2 mutation in the N-terminal transmembrane domain.

Expanding the phenotype of IFAP/BRESECK syndrome: a new case with severe hypogammaglobulinemia

The ichthyosis follicular with atrichia and photophobia syndrome (IFAP) is a rare X-linked multiple congenital malformation syndrome. Some male patients have additional features including brain anomalies, intellectual disability, ectodermal dysplasia, skeletal deformities, ear or eye anomalies and kidney dysplasia/hypoplasia (BRESEK syndrome) sometimes associated with Hirschsprung disease and cleft palate or cryptorchidism (BRESHECK syndrome). We report a 5 months-old male patient with the p.R429H mutation in MBTPS2 protein, which has been reported to be associated with the most severe phenotype of patients with IFAP/BRESHECK syndrome. This patient presented with a severe IFAP/BRESHECK phenotype including ichthyosis follicular, atrichia, photophobia, brain anomalies, global developmental delay, Hirschsprung disease and kidney hypoplasia. Additional features not previously reported in IFAP syndrome, include severe hypogammaglobulinemia and congenital rectourethral fistula.

Genotype-phenotype correlations emerging from the identification of missense mutations in MBTPS2

Missense mutations affecting membrane-bound transcription factor protease site 2 (MBTPS2) have been associated with Ichthyosis Follicularis with Atrichia and Photophobia (IFAP) syndrome with or without BRESHECK syndrome, with keratosis follicularis spinulosa decalvans, and Olmsted syndrome. This metalloprotease activates, by intramembranous trimming in conjunction with the protease MBTPS1, regulatory factors involved in sterol control of transcription and in cellular stress response. In this study, 11 different MBTPS2 missense mutations detected in patients from 13 unrelated families were correlated with the clinical phenotype, with their effect on cellular growth in media without lipids, and their potential role for sterol control of transcription. Seven variants were novel [c.774C>G (p.I258M); c.758G>C (p.G253A); c.686T>C (p.F229S); c.1427T>C (p.L476S); c.1430A>T (p.D477V); c.1499G>A (p.G500D); c.1538T>C (p.L513P)], four had previously been reported in unrelated sibships [c.261G>A (p.M87I); c.1286G>A (p.R429H); c.1424T>C (p.F475S); c.1523A>G (p.N508S)]. In the enzyme, the mutations cluster in transmembrane domains. Amino-acid exchanges near the active site are more detrimental to functionality of the enzyme and, clinically, associated with more severe phenotypes. In male patients, a genotype-phenotype correlation begins to emerge, linking the site of the mutation in MBTPS2 with the clinical outcome described as IFAP syndrome with or without BRESHECK syndrome, keratosis follicularis spinulosa decalvans, X-linked, Olmsted syndrome, or possibly further X-linked traits with an oculocutaneous component.

MBTPS2 mutation in a British pedigree with keratosis follicularis spinulosa decalvans

Keratosis follicularis spinulosa decalvans (KFSD; OMIM 308800) is an X-linked disorder characterized by widespread hyperkeratotic follicular papules (including keratosis pilaris-like lesions), facial erythema, hypotrichosis and scarring alopecia. KFSD results from mutations in the MBTPS2 gene. Mutations in this gene also underlie ichthyosis follicularis, alopecia and photophobia syndrome. We report a British pedigree with KFSD resulting from the mutation p.Asn508Ser. This particular mutation has been reported in three other pedigrees with KFSD (Dutch, American, British) and is the only pathogenic mutation reported in this disorder to date. However, the same mutation has also been reported in a Chinese pedigree with IFAP syndrome, highlighting the clinical heterogeneity and overlapping molecular pathology of these two disorders.

Ichthyosis follicularis, alopecia, and photophobia (IFAP) syndrome

The IFAP syndrome is a rare X-linked genetic disorder reported in nearly 40 patients. It is characterized by the triad of Ichthyosis Follicularis, Alopecia, and Photophobia from birth. Other features such as short stature, intellectual disability, and seizures may develop in the first few years of life. Skin histopathology is non-specific and consists of dilated hair follicles with keratin plugs extending above the surface of the skin, decreased or absent sebaceous glands, and decreased desmosomes in number and size. The disorder results from mutations in the MBTPS2 gene that impairs cholesterol homeostasis and the ability to cope with endoplasmic reticulum stress. Follicular hyperkeratosis can be treated using topical keratolytics, emollients and urea preparations. A moderate response to acitretin therapy has been noted in some patients. Intensive lubrication of the ocular surface is essential. Life expectancy in patients with IFAP syndrome can vary from death in the neonatal period to normal surviving. Cardiopulmonary complications remain the major cause of death.