Genetic information is organized into chromosomes within the nucleus of our cells. Humans typically have 46 chromosomes, arranged in 23 pairs, with one set inherited from each parent. Changes in these chromosomes can lead to variations in genetic material, affecting development and bodily functions.
What is 12p5
12p5 refers to a specific chromosomal abnormality most commonly associated with Pallister-Killian Syndrome (PKS). This condition involves an extra copy of genetic material from the short arm of chromosome 12. The “12” indicates chromosome 12, “p” denotes the short arm, and “5” refers to a specific band location on that short arm, indicating the region of duplication.
This abnormality is an isochromosome 12p [i(12p)], meaning two copies of the short arm of chromosome 12 are joined. This extra chromosome is present in some, but not all, cells of the body, a characteristic known as mosaicism, which is a hallmark of Pallister-Killian Syndrome.
Recognizable Features and Health Concerns
Individuals with 12p5 (Pallister-Killian Syndrome) often exhibit recognizable features and health challenges. Many affected infants experience extremely weak muscle tone (hypotonia), leading to difficulties with breathing, feeding, and the development of gross motor skills like sitting, standing, and walking.
Developmental delays are common, including intellectual disability and speech delays. Distinctive facial features are often observed, including a high, rounded forehead, widely spaced eyes, a broad nasal bridge, and low-set ears. Scalp hair may be sparse, particularly around the temples, and some individuals may have patches of unusual skin pigmentation.
Beyond these traits, various medical issues can affect different body systems. About 40% of affected infants are born with a congenital diaphragmatic hernia, a condition where a hole in the diaphragm allows abdominal organs to move into the chest. Other health concerns include heart defects, seizures, hearing loss, vision impairment, and skeletal abnormalities like extra fingers or toes.
Diagnosis and Support
Diagnosis of 12p5 (Pallister-Killian Syndrome) is primarily achieved through genetic testing. Methods like karyotyping, Fluorescence In Situ Hybridization (FISH), or chromosomal microarray detect the extra copy of the short arm of chromosome 12. Diagnosis can occur before birth through prenatal tests like amniocentesis or chorionic villus sampling, which analyze fetal cells.
After birth, diagnosis can be confirmed by examining cells from tissues like skin fibroblasts, as the mosaic nature means the abnormality might not be uniformly present in all cell types, such as blood cells. Management is supportive and multidisciplinary, focusing on addressing specific health concerns and developmental needs. This often involves therapies like physical, occupational, and speech therapy, along with specialized medical care.