The phenotypic spectrum of contiguous deletion of CYP21A2 and tenascin XB: quadricuspid aortic valve and other midline defects

Abstract

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is an autosomal recessive disorder and is the most common cause of ambiguous genitalia in the newborn. The genes encoding 21-hydroxylase, CYP21A2, and tenascin-X (TNX), TNXB, are located within the HLA complex, in a region of high gene density termed the RCCX module. The module has multiple pseudogenes as well as tandem repeat sequences that promote misalignment during meiosis leading to complex gene rearrangements, deletions and gene conversion events. CYP21A2 mutations cause CAH, and TNX deficiency has been identified as a cause of hypermobility type Ehlers-Danlos syndrome (EDS). Here we report on a three-generation family with a heterozygous deletion encompassing CYP21A2 and TNXB that initially came to medical attention due to the diagnosis of CAH in the proposita. Southern blotting and PCR-based analysis of the RCCX module revealed a CYP21A2 deletion extending into TNXB in one allele and a CYP21A2 point mutation in the other allele. Family history is notable for joint hypermobility. Additional radiological and clinical investigations showed a quadricuspid aortic valve, single kidney, bicornuate uterus and a bifid uvula in the proposita, and mitral valve prolapse in her mother. These findings further delineate the phenotype of the CAH-TNX contiguous gene deletion syndrome and point to an intersection of connective tissue dysplasias with a common gene-mediated endocrine disorder.

Fig. 1

Pedigree of the family. # Genetic analysis performed; Carrier of TNXB/XA fusion gene (CYP21A2 deletion); Carrier of CYP21A2 point mutation (In2G); Affected by CAH, compound heterozygote (TNXB/XA, In2G). Facial asymmetry with ipsilateral ear dysplasia and unilateral deafness, but normal intelligence.

Fig. 2

Phenotypic features include: A: bifid uvula (proposita); B: mild arachnodactyly (proposita); C: hyperextensible joints (proposita); D: hyperextensible joints (mother).

Fig. 3

A. Genomic structure of a bimodular haplotype for RCCX and deletions leading to two different fusion genes. Dashed lines (¦) indicate duplication boundaries. Vertical arrows (↓) indicate the locations of DNA probes and sizes of digested fragments from Southern blots. ■– TNXB-specific forward primer; ●– TNXB-specific reverse primer; ○– TNXA-specific reverse primer. The common 30 kb deletion in CAH patients, covering the TNXA-specific reverse primer, results in a non-functional CYP21A1P/21A2 fusion gene (middle panel). Recombination between TNXB and TNXA results in a deletion, TNXB/XA fusion gene and 2.4 kb product (lower panel). B. Southern blots detecting the TNXB/XA fusion gene. TaqI RFLP demonstrated the RCCX haplotype and gene contents at the RCCX locus (upper panel). PshAI RFLP confirmed RP genotyping (lower panel). The father had equal intensities from each gene pair (RP1:RP2, CYP21A2:CYP21A1P, TNXB:TNXA). The proposita had reduced intensities from CYP21A2 and TNXB, indicating a large deletion encompassing both genes. C4L, longer copy of C4; C4S, shorter copy of C4. C. PCR amplification of genomic DNA from five family members and a healthy control. A reaction with only water (no DNA) as template is also shown. All family members and the control demonstrated a 2.4 kb fragment produced by the TNXB-specific forward primer and TNXB-specific reverse primer (upper panel). The proposita, mother and maternal grandfather exhibited a 2.4 kb fragment produced by the TNXB-specific forward primer and TNX-specific reverse primer (lower panel), indicating heterozygosity for the TNXB/XA fusion gene. D. The haplotype organizations of RCCX in each subject with Southern blot.

FIG. 4

Cardiac magnetic resonance steady-state free precession images. The quadricuspid aortic valve is depicted in diastole (left) and in systole (right) with corresponding line drawings to label the anatomy. RA, right atrium; LA, left atrium; AoV, aortic valve; 1, 2, 3, 4 indicate cusps of the aortic valve.