Health Dictionary
Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.
Tetrasomy 9p
Introduction
Tetrasomy 9p is a rare genetic disease where the short arm of chromosome 9 (9p) appears not just twice in a base pair, but four times. The additional chromosome is called a “marker” or an isochromosome. It is considered a mosaic condition.