Population data suggest that deletions of 1p36 are a relatively common chromosome abnormality.

Monosomy 1p36 is a relatively common chromosome deletion. Deletion of this chromosome band can be difficult to visualize using routine cytogenetic banding techniques. The use of fluorescence in situ hybridization (FISH) with telomere region-specific probes has aided in the diagnosis of patients. In this study we ascertained 62 patients with deletions of 1p36 from 61 families and collected information regarding previous chromosome analyses, mode of ascertainment, clinical indication, age at diagnosis, and parental ages. The majority of deletions occur on the maternally derived chromosome. We identified terminal deletions, interstitial deletions, derivative chromosomes, and complex rearrangements. We correlated the type of rearrangement with the parental origins. Almost 50% of the patients had at least one chromosome analysis interpreted as normal. Retrospectively, 98% of deletions could be identified by routine chromosome analysis with careful attention to chromosome 1p36. Clinical indications were variable, with developmental delay/mental retardation being the most common. Increased maternal serum alpha fetoprotein (MSAFP) was detected in four of the five prenatally diagnosed cases. Maternal age at the time of birth of the affected child was significantly lower than the general United States population mean. We suggest a multistep approach for the diagnosis and clinical evaluation in cases of monosomy 1p36.