Adrenal insufficiency in paediatric patients is mostly due to congenital adrenal hyperplasia (CAH), a severe monogenic disease caused by steroid 21-hydroxylase deficiency (21-OHD, encoded by the CYP21A2 gene) in 95% of cases. CYP21A2 genotyping requires careful analyses that guaranty gene-specific PCR, accurate definition of pseudogene-gene chimeras, gene duplications and allele dropout avoidance. A small panel of well-established disease-causing alterations enables a high diagnostic yield in confirming/discarding the disorder not only in symptomatic patients but also in those asymptomatic with borderline/positive results of 17-hydroxyprogesterone. Unfortunately, the complexity of this locus makes it today reluctant to high throughput techniques of massive sequencing. The strong relationship existing between the molecular alterations and the degree of enzymatic deficiency has allowed genetic studies to demonstrate its usefulness in predicting/classifying the clinical form of the disease. Other aspects of interest regarding molecular studies include its independence of physiological variations and analytical interferences, its usefulness in the diagnosis of simple virilizing forms in males and its inherent contribution to the genetic counseling, an aspect of great importance taking into account the high carrier frequency of CAH in the general population. Genetic testing of CYP21A2 constitutes an irreplaceable tool to detect severe alleles not just in family members of classical forms but also in mild late-onset forms of the disease and couples. It is also helpful in areas such as assisted reproduction and preimplantation diagnosis. Molecular diagnosis of 21-OHD under expert knowledge definitely contributes to a better management of the disease in every step of the clinical course.

Molecular study has become an invaluable tool in the field of RASopathies. Treatment with recombinant human growth hormone is approved in Noonan syndrome but not in the other RASopathies. The aim of this study was to learn about the molecular base of a large cohort of patients with RASopathies, with particular emphasis on patients with pathogenic variants in genes other than PTPN11, and its potential impact on rGH treatment indication. We reviewed the clinical diagnosis and molecular findings in 451 patients with a genetically confirmed RASopathy. HRAS alterations were detected in only 2 out of 19 patients referred with a Costello syndrome suspicion, whereas pathogenic variants in RAF1 and SHOC2 were detected in 3 and 2, respectively. In 22 patients referred with a generic suspicion of RASopathy, including cardiofaciocutaneous syndrome, pathogenic alterations in classic Noonan syndrome genes (PTPN11, SOS1, RAF1, LZTR1, and RIT1) were found in 7 patients and pathogenic variants in genes associated with other RASopathies (HRAS, SHOC2, and PPPCB1) in 4. The correct nosological classification of patients with RASopathies is critical to decide whether they are candidates for treatment with rhGH. Our data illustrate the complexity of differential diagnosis in RASopathies, as well as the importance of genetic testing to guide the diagnostic orientation in these patients.

Objectives The chimeras causing the CAH-X syndrome (SCAH-X) result from recombination between CYP21A2-TNXB and their respective pseudogenes (CYP21A1P-TNXA). The clinical manifestations of this syndrome include congenital adrenal hyperplasia (CAH) and Ehlers–Danlos syndrome (EDS). Since SCAH-X has been recently described, the number of publications available is limited. The objective of this study was to set up a molecular approach and a screening algorithm for detecting CAH-X chimeras, determine their frequency and distribution in the Spanish population, and assess their clinical pattern of occurrence in a group of patients. Methods A total of 186 patients were eligible for CAH-X molecular genetic testing. Testing included MLPA, heterodimer detection by capillary gel electrophoresis, and sequencing of exons 40, 41, and 43 of TNXB. A review was performed of the medical history of 20 patients from three hospitals of reference and the signs and symptoms of EDS they exhibited. Results In total, 78 CAH patients were carriers of CAH-X chimeras (41.9 %). Forty-six patients were carriers of CH1 (24.7 %), 24 of CH2 (12.9 %), and 8 of CH3 (4.3 %), with a heterogeneous geographical distribution. Seven (35 %) of the 20 carriers of a CAH-X chimera who underwent clinical examination experienced clinical manifestations of EDS. Conclusions The impact of SCAH-X in the Spanish population was assessed by genetic testing. In the light of the clinical pattern of occurrence and significant prevalence of SCAH-X in the Spanish population, early diagnosis of this entity is essential for an appropriate follow-up of clinical manifestations.

Resumen Objetivos La recombinación entre CYP21A2-TNXB y sus respectivos pseudogenes (CYP21A1P-TNXA) da lugar a quimeras responsables del síndrome CAH-X (SCAH-X). Los pacientes con este síndrome presentan manifestaciones clínicas de hiperplasia suprarrenal congénita (HSC) y síndrome de Ehlers-Danlos (SED). La descripción del SCAH-X es reciente y es limitado el número de estudios disponibles. El objetivo de este trabajo es poner a punto un abordaje para la detección de todos los tipos de quimeras CAH-X, determinar su frecuencia y la distribución en población española así como valorar la expresividad clínica en un grupo de pacientes. Métodos se seleccionaron 186 pacientes candidatos al estudio molecular CAH-X. Dicho abordaje molecular incluyó la técnica MLPA, detección de heterodímeros por electroforesis en gel capilar y secuenciación de exones 40, 41 y 43 de TNXB. La revisión de historias clínicas y la evaluación de signos y síntomas SED se ha llevado a cabo en 20 pacientes de tres Hospitales de referencia. Resultados Setentaiocho pacientes HSC presentaron quimeras CAH-X (41,9 %). Se detectaron 46 quimeras CH1 (24,7 %), 24 CH2 (12,9 %) y 8 CH3 (4,3 %), con una distribución geográfica no homogénea. Siete de los 20 portadores de quimera CAH-X valorados clínicamente (35 %) presentaron manifestaciones clínicas asociadas a SED. Conclusiones La implementación del abordaje molecular descrito en este trabajo ha permitido determinar el impacto del SCAH-X en población española. La expresividad clínica detectada y la considerable prevalencia del SCAH-X hacen recomendable el diagnóstico temprano de esta entidad para realizar un adecuado seguimiento de las manifestaciones clínicas que lo caracterizan.