Cytogenetic Analysis of Children With Developmental Delay Referred to a Genetic Clinic

Abstract

Children who are late to sit, walk, speak or learn are often referred to a genetics clinic, and one of the first questions asked is whether a chromosome change lies behind the delay. Cytogenetic testing has changed a great deal over the last few decades, from banded karyotypes through fluorescence in situ hybridisation to chromosomal microarray, and the meaning of a normal or abnormal result has changed with it. This narrative review describes what each cytogenetic method can and cannot detect, how findings are interpreted, and why reports of diagnostic yield from different clinics are hard to compare. It draws on published guidelines and primary studies and reports no new data and no patient series. Karyotyping remains the right tool for some questions, notably balanced rearrangements and suspected aneuploidy syndromes, whereas microarray detects small gains and losses that a karyotype cannot see and is widely recommended as a first-tier test. Neither method finds single-gene variants, repeat expansions or most epigenetic changes, so a negative cytogenetic result narrows the search without ending it. Variants of uncertain significance, referral criteria and the order of testing all influence reported yield. The review ends with a short list of what a reader should look for before trusting a stated figure.