Proximal chromosome 18q deletion syndrome is a chromosome abnormality that occurs when there is a missing (deleted) copy of genetic material from the part of the long (q) arm near the center of chromosome 18. The severity of the condition and the signs and symptoms depend on the size and location of the deletion and which genes are involved. Features that often occur in people with Proximal chromosome 18q deletion syndrome include developmental delay, intellectual disability, and distinctive facial features. The might also have seizures, low muscle tone (hypotonia), speech and language delays, obesity, and short stature. Chromosome testing of both parents can provide more information on whether or not the deletion was inherited. In most cases, parents do not have any chromosomal anomaly. However, sometimes one parent is found to have a balanced translocation, where a piece of a chromosome has broken off and attached to another one with no gain or loss of genetic material. The balanced translocation normally does not cause any signs or symptoms, but it increases the risk for having a child with a chromosomal anomaly like a deletion.