Genetic Testing Methodologies

Karyotyping

Conventional cytogenetic analysis examines chromosomes at the metaphase stage, detecting both balanced and unbalanced structural abnormalities as well as numerical chromosomal abnormalities, with a limited resolution of approximately 5-10 Mb and a diagnostic yield of approximately 3.7% in children with global developmental delay 1, 2, 3
The American College of Medical Genetics recommends karyotyping for suspected common aneuploidies, evaluation of balanced rearrangements, family history of chromosomal rearrangement in phenotypically normal individuals, and cases of multiple miscarriages 1, 4

Microarray analysis is a high-resolution, whole-genome technique that detects copy number variations at a resolution of 50-100 kb, with a higher diagnostic yield than karyotyping, approximately 10%, and allows simultaneous analysis of hundreds or thousands of genomic loci 2, 5, 6
The American College of Medical Genetics recommends microarray analysis as a first-line test for individuals with developmental delays, multiple anomalies, or autism spectrum disorders, and for clarifying chromosome abnormalities detected by G-band analysis 1, 4
Microarray analysis has limitations, including the inability to detect balanced chromosomal rearrangements, limited ability to detect low-level mosaicism, and cannot determine chromosomal mechanisms of genetic imbalance 1, 5, 4

The American College of Medical Genetics recommends karyotyping for suspected common aneuploidies and microarray analysis for first-line testing of individuals with multiple anomalies or developmental delays 1, 4
Microarray analysis is useful for detecting copy number variations, but cannot detect balanced rearrangements or point mutations, and may identify variants of uncertain significance requiring parental testing 2, 5, 4

The presence of one X and one Y chromosome is consistent with typical male development, as stated by the American College of Medical Genetics and Genomics 7, 8
No further confirmatory testing is needed since no abnormalities were identified, according to the American College of Medical Genetics and Genomics 9, 10

Microarray analysis has limited sensitivity for low-level mosaicism, with mosaicism below approximately 20-30% possibly not being reliably detected, as noted by the American College of Medical Genetics and Genomics 7, 11

If clinical suspicion remains high for a specific genetic condition, consider targeted gene sequencing, exome sequencing, or karyotyping if balanced rearrangements are suspected based on family history or phenotype, as recommended by the American College of Medical Genetics and Genomics 12, 13
If sex chromosome mosaicism is clinically suspected, traditional karyotyping may be more sensitive for detecting low-level mosaicism than microarray, according to the American College of Medical Genetics and Genomics 7, 11

Do not order reflexive confirmatory testing since no abnormalities were detected, as stated by the American College of Medical Genetics and Genomics 9, 10
If clinical features suggest a genetic condition despite normal microarray, pursue alternative testing strategies based on the specific clinical presentation, as recommended by the American College of Medical Genetics and Genomics 12, 13

Chromosomal microarray platforms (CGH‑based or SNP‑based) identify only DNA copy‑number gains and losses, thereby detecting unbalanced chromosomal abnormalities but cannot detect balanced rearrangements, ploidy changes, or nucleotide‑level mutations such as point mutations and small repeat expansions 14, 15, 16, 17, 18.
A normal microarray result does not rule out the presence of nucleotide‑base‑pair changes in any gene that is represented on the array, meaning pathogenic variants can be missed even when the array appears unremarkable 19, 20.

The reliable detection threshold for copy‑number variants is generally ≥ 400 kb across the genome; specialized enriched regions may allow detection of smaller CNVs, but the routine resolution remains limited 21.

Because PHOX2B pathogenic variants are predominantly point mutations and polyalanine repeat expansions, they fall outside the detection range of standard microarray analysis [14‑18].
Consequently, a normal microarray cannot be used to exclude PHOX2B‑related diseases (e.g., congenital central hypoventilation syndrome, Hirschsprung disease, neuroblastoma). The test is designed for chromosomal imbalances, not gene‑level mutations 19, 20.
Failure to detect an alteration at the PHOX2B locus on microarray does not exclude any other type of anomaly at that locus, reinforcing the need for sequencing‑based approaches when clinical suspicion is high 20.