Microdeletion 1p36 is probably the most common terminal microdeletion occurring with a frequency of 1:5,000 to 1:10,000. It causes 1p36 microdeletion syndrome also known as monosomy 1p36 syndrome. Most patients have a moderate to severe developmental disorder with severe impairment of expressive speech, muscle hypotonia, and growth retardation. External features include: a large anterior fontanel that closes late, deep-set eyes, horizontal eyebrows, broad nasal root, hypoplastic midface, low-set dysplastic ears, very pointed chin, brachydactyly and camptodactyly, and short feet. Obesity and hyperphagia are described in some patients. Congenital heart defects are present in about 70% and noncompaction cardiomyopathy in 23%. Almost all patients present with abnormal ECG, and nearly half also have seizures. Visual and hearing disturbances are also present in more than half of the patients.
Microdeletion 1p36 is usually detected by subtelomeric diagnosis or increasingly by chromosomal microarray; in individual cases, it can be diagnosed by light microscopy using a high-resolution banding technique (between 600 and 800 bands) in chromosomal analysis.
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