The basis of Triple A syndrome; a large deletion in the AAAS gene causes the disease in a child
The basis of Triple A syndrome; a large deletion in the AAAS gene causes the disease in a child
Sara Pourshaikhali,1Nasrollah Saleh-Gohari,2,*Kolsoum Saeidi,3
1. Department of Medical Genetics, Afzalipour School of Medicine, Kerman University of Medical Sciences 2. Department of Medical Genetics, Afzalipour School of Medicine, Kerman University of Medical Sciences
Introduction: Triple A syndrome, also known as Allgrove syndrome, is a rare autosomal recessive disorder. It is characterized by a triad of symptoms: adrenal insufficiency (Addison's disease), alacrima (reduced or absent tear production), and achalasia (failure of the smooth muscles of the esophagus to relax). The condition tends to manifest in childhood or adolescence, and additional symptoms such as autonomic dysfunction and neurological abnormalities may also be present. This syndrome is an extremely rare condition, and its exact frequency is not well-established. Due to its rarity, it can often go undiagnosed or misdiagnosed, leading to challenges in gathering accurate data on its prevalence. Here, we have found an extensive large deletion in AAAS gene in a 5-year-old girl with adrenal insufficiency.
Methods: 1. Gene Selection for Assessment: Considering the clinical manifestations of the proband closely resembling triple A syndrome, we opted to investigate the importance of the AAAS gene on 12q13.13. This gene is widely recognized as the key determinant of Triple A syndrome.
2. Whole Exome Sequencing (WES):
2.1. Proband Sample: We collected peripheral blood from the proband and employed Whole Exome Sequencing using the Illumina HiSeq4000 platform. The sequencing process utilized a read length of 101 base pairs and achieved a coverage of 100x. The Laboratory for Molecular Diagnosis at the University of Leuven conducted this test. 2.2. Parental Samples: Since the couple previously had a male child with ambiguous genitalia, we requested Whole Exome Sequencing to analyze 219 genes associated with disorders of sex development. The objective was to identify potential single point mutations and small indels linked to this phenotype. For this purpose, we utilized the Twist Human Core Exome kit and performed library sequencing on the Illumina platform. The sequencing achieved a basic coverage of 316x with a mean no-target range of 102x. CeGaT GmbH in Germany conducted the sequencing. The NGS method's analytical sensitivity and specificity in the assay were assumed to be >95%.
3. Genomic Amplification by Polymerase Chain Reaction (GAP PCR) To ascertain if the observed large deletion in the proband was a newly occurring mutation or one inherited from the parents, simultaneous Gap PCR was performed in the proband and the parents.
Results: A significant finding in this study was the identification of a homozygous large deletion spanning exons 3, 4, 5, 6, and 7 (MN_015665) of the AAAS gene. The deletion, located in the genomic region 12:53707985-53709653, is approximately 7000 bp in length. This deletion strongly correlates with the clinical manifestations observed, confirming a definitive diagnosis of Triple A syndrome in the proband.
Interestingly, no mutations were detected in the sex development genes of the parents. The WES results did not reveal any large duplications, deletions, translocations, ploidy changes, or uniparental disomies associated with sex development disorders. However, two heterozygous variants of uncertain significance (VUS) were identified in the FRAS1 gene (c.2138-6C>T) and the TRIM32 gene (c.370C>T) specifically in the father's parents.
Furthermore, the proband has inherited Triple A syndrome from her carrier parents, as confirmed by GAP PCR analysis. This analysis revealed a large heterogeneous deletion of the AAAS gene (region 12:53707985-53709653) in a homozygous form, matching the deletion identified in the proband's parents.
Conclusion: Our proband showed all three main clinical features and some other rare manifestations like hyperpigmentation. By identifying heterozygote disease-related mutations in the parents, prenatal diagnosis for later pregnancies was suggested for the couple.