Will a chromosomal microarray detect PHOX2B gene abnormalities?

Will Chromosomal Microarray Detect PHOX2B Gene Abnormalities?

Chromosomal microarray will NOT reliably detect PHOX2B gene abnormalities because this testing modality only identifies copy number variations (deletions and duplications) and cannot detect the point mutations and small polyalanine repeat expansions that cause the vast majority of PHOX2B-related disorders.

Understanding Microarray Limitations

Microarray analysis by CGH-based or SNP-based arrays can detect DNA copy number gains and losses only, thereby identifying unbalanced chromosome abnormalities, but this technique cannot detect balanced rearrangements, some ploidy changes, and mutations (nucleotide base pair changes). 1

• Current microarray analysis technologies will detect only gains and losses of genomic segments at a resolution of approximately 50-100 kb genome-wide 2
• A normal microarray result does not exclude mutations (nucleotide base-pair changes) in any gene represented on the microarray 1
• The typical resolution threshold is 400 kb or larger for reliable detection, though enriched regions may detect smaller CNVs 1

Why PHOX2B Mutations Are Missed

PHOX2B pathogenic variants are predominantly point mutations and polyalanine repeat expansions, not large deletions or duplications detectable by microarray. 3, 4, 5

• The novel missense mutation c.422G > A (p.Arg141Gln) in PHOX2B represents the type of single nucleotide change that microarray cannot detect 4
• PHOX2B mutations are associated with congenital central hypoventilation syndrome (CCHS), Hirschsprung disease, and neuroblastoma predisposition, but genotyping of specific PHOX2B pathogenic variants requires sequencing-based methods 5
• Nonpolyalanine repeat PHOX2B pathogenic variants have been identified in patients with both neuroblastoma and late-onset CCHS, but these require targeted gene sequencing for detection 3

Appropriate Testing Strategy for PHOX2B

When clinical suspicion exists for PHOX2B-related disorders (CCHS, Hirschsprung disease, or familial neuroblastoma), order targeted PHOX2B gene sequencing or exome sequencing, not chromosomal microarray. 2

• Genotyping of a PHOX2B pathogenic variant is required to establish a diagnosis of CCHS 5
• Whole-exome sequencing combined with Sanger sequencing confirmation is the appropriate methodology for detecting PHOX2B mutations 4
• If microarray analysis yields normal results but clinical features suggest a genetic condition, pursue alternative testing strategies including targeted gene sequencing or exome sequencing based on the specific clinical presentation 2

Common Clinical Pitfall

Do not assume that a normal microarray result excludes PHOX2B-related disease. The microarray is designed to detect chromosomal imbalances, not gene-level mutations 1. Failure to detect an alteration at any locus does not exclude all anomalies at that locus 1. If the clinical phenotype includes central hypoventilation, Hirschsprung disease, neuroblastoma, or autonomic nervous system dysfunction, proceed directly to PHOX2B gene sequencing regardless of microarray results 5.