A novel nonsense mutation in the STS gene in a Pakistani family with X-linked recessive ichthyosis: including a very rare case of two homozygous female patients

Revisiting X-linked congenital ichthyosis

X-linked recessive ichthyosis (XLI) is a hereditary skin disease characterized by generalized dryness and scaling of the skin, with frequent extracutaneous manifestations. It is the second most common type of ichthyosis, with a prevalence of 1/6,000 to 1/2,000 in males and without any racial or geographical differences. The causative gene for XLI is the steroid sulfatase gene (STS), located on Xp22.3. STS deficiency causes an abnormal cholesterol sulfate (CS) accumulation in the stratum corneum (SC). Excess CS induces epidermal permeability barrier dysfunction and scaling abnormalities. This review summarizes XLI's genetic, clinical, and pathological features, pathogenesis, diagnosis and differential diagnoses, and therapeutic perspectives. Further understanding the role of the STS gene pathogenic variants in XLI may contribute to a more accurate and efficient clinical diagnosis of XLI and provide novel strategies for its treatment and prenatal diagnosis.

Structures and functions of human placental aromatase and steroid sulfatase, two key enzymes in estrogen biosynthesis

Cytochrome P450 aromatase (AROM) and steroid sulfatase (STS) are the two key enzymes for the biosynthesis of estrogens in human, and maintenance of the critical balance between androgens and estrogens. Human AROM, an integral membrane protein of the endoplasmic reticulum, is a member of the cytochrome P450 superfamily. It is the only enzyme to catalyze the conversion of androgens with non-aromatic A-rings to estrogens characterized by the aromatic A-ring. Human STS, also an integral membrane protein of the endoplasmic reticulum, is a Ca2+-dependent enzyme that catalyzes the hydrolysis of sulfate esters of estrone and dehydroepiandrosterone to the unconjugated steroids, the precursors of the most potent forms of estrogens and androgens, namely, 17β-estradiol, 16α,17β-estriol, testosterone and dihydrotestosterone. Expression of these steroidogenic enzymes locally within organs and tissues of the endocrine, reproductive, and central nervous systems is the key for maintaining high levels of the reproductive steroids. The enzymes have been drug targets for the prevention and treatment of diseases associated with steroid hormone excesses, especially in breast, endometrial and prostate malignancies. Both enzymes have been the subjects of vigorous research for the past six decades. In this article, we review the important findings on their structure-function relationships, specifically, the work that began with unravelling of the closely guarded secrets, namely, the 3-D structures, active sites, mechanisms of action, origins of substrate specificity and the basis of membrane integration. Remarkably, these studies were conducted on the enzymes purified in their pristine forms from human placenta, the discarded and their most abundant source. The purification, assay, crystallization, and structure determination methodologies are described. Also reviewed are their functional quaternary organizations, post-translational modifications and the advancements made in the structure-guided inhibitor design efforts. Outstanding questions that still remain open are summarized in closing.

Prenatally detected six duplications at Xp22.33-p11.22: a case report

BACKGROUND

The discrepancy between the results of cytogenetics and the results of chromosome microarray analysis (CMA) has often led to confusion over genetic counselling for prenatal diagnosis.

CASE PRESENTATION

The prenatal ultrasound results of a congenital heart defect (CHD) foetus displayed an apartial endocardial pad defect and permanently dilated coronary sinus and left superior vena cava at 21 weeks of gestation. Cytogenetic analysis, CMA, fluorescent in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA) with foetal cord blood samples were used to detect the genetic aetiology. Routine G-binding cytogenetic analysis showed normal karyotypes in both the foetus' and parents' blood samples. CMA results demonstrated that there were 53.973-Mb recurrent CNVs at Xp22.33-p11.22, as confirmed by MLPA assay.

CONCLUSIONS

Herein, we described the CNV of six duplications at Xp22.33-p11.22 and the 53.973 Mb duplication CNV that was not found in foetal cord blood samples by conventional cytogenetic methods, and it was confirmed by CMA and MLPA. Our novel findings will provide helpful information for prenatal diagnosis and genetic counselling for foetal CHDs.

Ichthyosis

The ichthyoses are a large, heterogeneous group of skin cornification disorders. They can be inherited or acquired, and result in defective keratinocyte differentiation and abnormal epidermal barrier formation. The resultant skin barrier dysfunction leads to increased transepidermal water loss and inflammation. Disordered cornification is clinically characterized by skin scaling with various degrees of thickening, desquamation (peeling) and erythema (redness). Regardless of the type of ichthyosis, many patients suffer from itching, recurrent infections, sweating impairment (hypohidrosis) with heat intolerance, and diverse ocular, hearing and nutritional complications that should be monitored periodically. The characteristic clinical features are considered to be a homeostatic attempt to repair the skin barrier, but heterogeneous clinical presentation and imperfect phenotype-genotype correlation hinder diagnosis. An accurate molecular diagnosis is, however, crucial for predicting prognosis and providing appropriate genetic counselling. Most ichthyoses severely affect patient quality of life and, in severe forms, may cause considerable disability and even death. So far, treatment provides only symptomatic relief. It is lifelong, expensive, time-consuming, and often provides disappointing results. A better understanding of the molecular mechanisms that underlie these conditions is essential for designing pathogenesis-driven and patient-tailored innovative therapeutic solutions.