The term ‘differences of sex development’ (DSD) refers to a group of congenital conditions that are associated with atypical development of chromosomal, gonadal, or anatomical sex. Disorders of steroidogenesis comprise autosomal recessive conditions that affect adrenal and gonadal enzymes and are responsible for some conditions of 46,XX DSD where hyperandrogenism interferes with chromosomal and gonadal sex development. Congenital adrenal hyperplasias (CAHs) are disorders of steroidogenesis that mainly involve the adrenals (21-hydroxylase and 11-hydroxylase deficiencies) and sometimes the gonads (3-beta-hydroxysteroidodehydrogenase and P450-oxidoreductase); in contrast, aromatase deficiency mainly involves the steroidogenetic activity of the gonads. This review describes the main genetic, biochemical, and clinical features that apply to the abovementioned conditions. The activities of the steroidogenetic enzymes are modulated by post-translational modifications and cofactors, particularly electron-donating redox partners. The incidences of the rare forms of CAH vary with ethnicity and geography. The elucidation of the precise roles of these enzymes and cofactors has been significantly facilitated by the identification of the genetic bases of rare disorders of steroidogenesis. Understanding steroidogenesis is important to our comprehension of differences in sexual development and other processes that are related to human reproduction and fertility, particularly those that involve androgen excess as consequence of their impairment.

Congenital adrenal hyperplasia (CAH) is mainly caused by the deficiency of the 21-hydroxylase enzyme coded by the CYP21A2 gene. However, some alleles in the non-classical form (NC-CAH) remain without identified mutations, suggesting the involvement of regulatory regions. Our objective was to study an allele carrying the variant *13 G>A in the 3'UTR of the CYP21A2 gene identified in some patients with a mild form of NC-CAH in order to verify the possible implication of this variation with the phenotype observed. Among all the subjects in whom the CYP21A2 gene was analyzed, 14 patients and 7 relatives heterozygous or homozygous for the *13 G>A substitution in 3'UTR were selected. Sequencing of DNA, genotyping, multiplex ligation-dependent probe amplification (MLPA), in vitro studies and bioinformatic analysis were performed. The haplotype of the *13 G>A allele was identical in all the subjects with a monomodular structure composed by one C4A gene and one CYP21A2 gene without a second module with the CYP21A1P pseudogene. No other concomitant mutations were found in the region extending from 3 kb in the promoter and encompassing the polyadenylation signal. Both bioinformatic analysis and in vitro studies predicted an alteration of the RNA folding and expression, but no miRNA target sequences were found in this region. The identification of a substitution in the 3'UTR of the gene associated with a mild form of NC-CAH suggests the importance of analyzing the CYP21A2 untranslated regions to better characterize and treat this subgroup of patients.

Background/Objectives: Biotinidase deficiency (BD) is a treatable autosomal recessive disorder included in many newborn screening (NBS) programs. The importance of early diagnosis and treatment is now well established. However, recent studies are emerging on the possibility of increased enzyme activity with age, an observation that raises questions about the long-term validity of the initial classification of these patients. This study aimed to assess the incidence, genetic and clinical features, and, notably, the longitudinal enzymatic trajectory of BD in a cohort identified by NBS in Emilia-Romagna, Italy, with implications for diagnostic re-evaluation and therapeutic decisions. Methods: A retrospective and prospective analysis was conducted on 64 infants recalled after NBS for suspected BD between 2016 and 2020. Biochemical, molecular, and clinical data were collected, and biotinidase (BTD) activity was monitored longitudinally. Affected individuals were supplemented with biotin and followed clinically for at least 5 years. Results: Thirty-one patients were diagnosed with BD (30 partial, 1 profound; incidence 1:5448). A significant and sustained increase in BTD activity was observed from diagnosis through early childhood (p < 0.001 up to 60 months), particularly among patients carrying the p.Asp444His variant. This enzymatic trend suggests a potential remodulation of biochemical classification over time. Genotype–phenotype concordance was high (92%), and clinical outcomes were favorable across the cohort. Conclusions: This study provides new evidence that BTD activity in patients with BD increases progressively, supporting the concept of age-dependent enzyme recovery. Our results support the need for systematic re-evaluation of diagnosis and treatment, especially at 12 months of age, and particularly in patients with evidence of partial activity deficiency and the p.Asp444His mutation.

Background: Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a monogenic disease having a prevalence of 1:400–1000 live births. Depending on kidney imaging, patients can be subdivided into Class 1 (typical) and Class 2 (atypical). The present study aims to provide better assessment of Class 2 patients to help define their family history, together with their clinical and radiological characteristics. Methods: One hundred twenty-four PKD patients with abdominal Magnetic Resonance Imaging (MRI) for the staging of ADPKD, were retrospectively analyzed, aiming to focus on Class 2 ADPKD patients. Total kidney volume and total cyst volume were evaluated, while also assessing their clinical and genetic characteristics. Results: Twelve patients fulfilled the Mayo criteria for Class 2 ADPKD (two Class 2B and ten Class 2A). Extrarenal involvement was observed in 66.7% of cases, but only two subjects presented an estimated Glomerular Filtration Rate (eGFR) < 60 mL/min/1.73 m ² . A positive family history for cystic disease was more frequent compared to other published cohorts. Only 8.3% tested positive for a likely pathogenic mutation in the PKD 1 gene. Class 2B patients showed a lower height-adjusted total kidney volume, with a lower percentage of total cyst volume. Conclusion: Based on our results, atypical ADPKD does not represent an uncommon condition, being present in about 10% of MRI-evaluated patients diagnosed with ADPKD. Genetic tests are frequently negative for PKD1/PKD2 , and total cyst volume and residual tissue volume do not increase the prognostic value of MRI in patients with these radiological characteristics. Other tools are needed to better characterize their kidney prognosis. Graphical

Sommario: La ricerca di varianti patogenetiche del gene CYP21A2, responsabili del 90–95% dei casi di iperplasia surrenale congenita, è resa altamente complessa dall’omologia di sequenza con lo pseudogene, dall’elevata frequenza di ricombinazione del locus e dal numero variabile di moduli ripetuti. Tuttavia, grazie alle recenti conoscenze e alle nuove metodiche si sono raggiunti ottimi livelli diagnostici importanti per una corretta diagnosi e una consulenza genetica affidabile, nonché per individuare patologie associate.