Mapping of a de novo unequal crossover causing a deletion of the steroid 21-hydroxylase (CYP21A2) gene and a non-functional hybrid tenascin-X (TNXB) gene

TNXA (also known as XA) is a truncated pseudogene of 5.7 kb that not only lacks most of the coding sequence of TNXB but also has a 120 bp deletion (indicated by the small triangle) spanning an exon-intron boundary. 10, 12, 17 CYP21A2 (also known as CYP21B) is the active steroid 21-hydroxylase gene; CYP21A1P (also known as CYP21A) is a full size pseudogene containing several deleterious mutations throughout its sequence, including three in phase stop codons. 9 The C4 genes express variants of the fourth component of complement with different affinities, known as C4A and C4B. [...]the current report clearly illustrates that a de novo recombination may be a pitfall in understanding RCCX haplotypes, emphasising the importance of studying entire families rather than isolated patients.