SNP Shot: Genomic Insights

Pierre Robin sequence is a group of facial and head abnormalities characterized by three main features: a small lower jaw (micrognathia), a tongue positioned further back in the mouth than usual (glossoptosis), and airway obstruction. Most individuals with Pierre Robin sequence also have a cleft palate, though its presence is not always considered essential for diagnosis, and opinions among medical professionals vary.

Pierre Robin sequence can occur independently or as part of a broader syndrome affecting other organs and tissues, such as Stickler syndrome or campomelic dysplasia. When associated with such a syndrome, it's called "syndromic" Pierre Robin sequence. When it occurs alone, it's termed "nonsyndromic" or "isolated" Pierre Robin sequence. Around 20 to 40 percent of Pierre Robin sequence cases are isolated.

The term "sequence" is used because the underdeveloped lower jaw (mandible) triggers a chain of events during prenatal development, leading to the other characteristics. The small jaw affects tongue positioning, and the abnormally positioned tongue can then block the airways. Furthermore, micrognathia and glossoptosis disrupt palate formation during fetal development, often resulting in a cleft palate.

The combined features of Pierre Robin sequence can cause breathing difficulties and feeding problems in infancy. Consequently, some affected infants may experience failure to thrive, meaning they don't grow and gain weight as expected. However, the lower jaw may eventually grow to a normal size in some children with Pierre Robin sequence, resulting in a normal-sized chin in adulthood.

Inheritance:

Isolated Pierre Robin sequence is typically not inherited but arises from new (de novo) genetic changes, occurring in individuals without a family history of the condition. Inherited cases of isolated Pierre Robin sequence usually follow an autosomal dominant inheritance pattern, meaning only one copy of the altered gene in each cell is enough to cause the condition. Syndromic Pierre Robin sequence is inherited according to the inheritance pattern of the underlying syndrome it's associated with.