Ichthyosis follicularis, alopecia, and photophobia (IFAP) syndrome due to mutation of the gene MBTPS2 in a large Australian kindred

Emerging Landscape of Osteogenesis Imperfecta Pathogenesis and Therapeutic Approaches

Osteogenesis imperfecta (OI) is an uncommon genetic disorder characterized by shortness of stature, hearing loss, poor bone mass, recurrent fractures, and skeletal abnormalities. Pathogenic variations have been found in over 20 distinct genes that are involved in the pathophysiology of OI, contributing to the disorder's clinical and genetic variability. Although medications, surgical procedures, and other interventions can partially alleviate certain symptoms, there is still no known cure for OI. In this Review, we provide a comprehensive overview of genetic pathogenesis, existing treatment modalities, and new developments in biotechnologies such as gene editing, stem cell reprogramming, functional differentiation, and transplantation for potential future OI therapy.

Mutations in SREBF1, Encoding Sterol Regulatory Element Binding Transcription Factor 1, Cause Autosomal-Dominant IFAP Syndrome

IFAP syndrome is a rare genetic disorder characterized by ichthyosis follicularis, atrichia, and photophobia. Previous research found that mutations in MBTPS2, encoding site-2-protease (S2P), underlie X-linked IFAP syndrome. The present report describes the identification via whole-exome sequencing of three heterozygous mutations in SREBF1 in 11 unrelated, ethnically diverse individuals with autosomal-dominant IFAP syndrome. SREBF1 encodes sterol regulatory element-binding protein 1 (SREBP1), which promotes the transcription of lipogenes involved in the biosynthesis of fatty acids and cholesterols. This process requires cleavage of SREBP1 by site-1-protease (S1P) and S2P and subsequent translocation into the nucleus where it binds to sterol regulatory elements (SRE). The three detected SREBF1 mutations caused substitution or deletion of residues 527, 528, and 530, which are crucial for S1P cleavage. In vitro investigation of SREBP1 variants demonstrated impaired S1P cleavage, which prohibited nuclear translocation of the transcriptionally active form of SREBP1. As a result, SREBP1 variants exhibited significantly lower transcriptional activity compared to the wild-type, as demonstrated via luciferase reporter assay. RNA sequencing of the scalp skin from IFAP-affected individuals revealed a dramatic reduction in transcript levels of low-density lipoprotein receptor (LDLR) and of keratin genes known to be expressed in the outer root sheath of hair follicles. An increased rate of in situ keratinocyte apoptosis, which might contribute to skin hyperkeratosis and hypotrichosis, was also detected in scalp samples from affected individuals. Together with previous research, the present findings suggest that SREBP signaling plays an essential role in epidermal differentiation, skin barrier formation, hair growth, and eye function.

Cholesterol homeostasis: Links to hair follicle biology and hair disorders

Lipids and lipid metabolism are critical factors in hair follicle (HF) biology, and cholesterol has long been suspected of influencing hair growth. Altered cholesterol homeostasis is involved in the pathogenesis of primary cicatricial alopecia, mutations in a cholesterol transporter are associated with congenital hypertrichosis, and dyslipidaemia has been linked to androgenic alopecia. The underlying molecular mechanisms by which cholesterol influences pathways involved in proliferation and differentiation within HF cell populations remain largely unknown. As such, expanding our knowledge of the role for cholesterol in regulating these processes is likely to provide new leads in the development of treatments for disorders of hair growth and cycling. This review describes the current state of knowledge with respect to cholesterol homeostasis in the HF along with known and putative links to hair pathologies.

Clinical and molecular characterization and response to acitretin in three families with Sjögren-Larsson syndrome

INTRODUCTION

Sjögren-Larsson syndrome (SLS) is a rare congenital disorder characterized by the triad of ichthyosis, spasticity, and mental retardation. Patients are usually referred to dermatology clinics during infancy. As paraplegia becomes the most debilitating symptom of the disease within a few years, ichthyosis, although a major burden for the patient, takes a back seat. Optimum treatment of ichthyosis in these children and the effect of treatment on different aspects such as severity of the ichthyosis, pruritus, or quality of life of the patients' and their caregivers is not well established.

MATERIALS AND METHODS

Genetic background of eight patients from three families diagnosed clinically with SLS was determined with whole-exome and Sanger sequencing. Clinical phenotypes, laboratory findings, magnetic resonance imaging (MRI), and treatment of the ichthyosis with acitretin were assessed.

RESULTS

All patients had the classical triad of Sjögren-Larsson syndrome. Genetic analysis revealed that one patient had a novel c.799-1 (+/+) homozygous splicing mutation in the ALDH3A2 gene. Other patients had the c.683G>A p.R228H (NM_000382.2) mutation in the same gene. Other manifestations included skeletal anomalies, enamel hypoplasia, bilateral T2-hyperintensities in white matter, and moderate-severe pruritus. Acitretin treatment in a maintenance dose of 0.25 mg/kg/day decreased the severity of ichthyosis in all children. It increased quality of life significantly in all of the children and their caregivers.

CONCLUSION

We conclude that ichthyosis can be treated effectively with low-dose acitretin in children with Sjögren-Larsson syndrome, and this treatment is associated with a significant improvement in the quality of life.

Hodgkin Lymphoma in a Patient With IFAP Syndrome: A Case Report and Review of Literature

The IFAP syndrome is a rare X-linked recessive inheritance disorder with defect of the MBTPS2 gene defined by the triad of follicular ichthyosis, alopecia, and photophobia. A total of 40 cases has been reported, but no correlation with Hodgkin lymphoma has been reported yet. A 3.5-year-old boy was diagnosed with IFAP syndrome confirmed by Next Generation Sequencing. He was on regular follow-up when he developed prolonged fever and lymphadenopathy. His lymph node biopsy showed Hodgkin lymphoma with mixed cellularity subtype. This case is the first report on IFAP syndrome associated with malignancy. IFAP syndrome could be a risk factor in developing malignancy.

Ocular manifestations of genetic skin disorders

Genetic skin diseases, or genodermatoses, often have extracutaneous manifestations. Ocular manifestations in particular can have significant clinical implications, like blindness. Other manifestations, such as the corneal opacities that occur in X-linked ichthyosis, are asymptomatic but characteristic of a particular genodermatosis. Ophthalmologic examination can aid in diagnosis when characteristic findings are seen. The genodermatoses with ocular manifestations will be reviewed, but neurocutaneous, syndromes, genetic pigmentary disorders, and genetic metabolic diseases are not included because they are covered elsewhere in this issue.

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.

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.