Testing the inheritance pattern of palmaris longus muscle absence

The palmaris longus muscle is among the most anatomically variable muscles in the human body and is often absent. Its absence is known to be inherited, yet the precise mode of genetic transmission remains uncertain. This study aimed to determine the prevalence of this muscle's absence in a sample of randomly selected families across several generations (parents and their biological children) and to assess the pattern of inheritance related to the presence or absence of the muscle.

A total of 82 individuals (39 males and 43 females) from 20 families, consisting of fathers, mothers, and all their joint offspring, were examined. The presence of the muscle was assessed bilaterally using Schaeffer's test along with additional clinical maneuvers. Descriptive statistical methods, including absolute and relative frequencies, were applied, and results were presented in both graphical and tabular formats.

Analysis revealed that the palmaris longus muscle was absent in a greater proportion of individuals (59.75%) than it was present (40.25%). In 80% of the families (16 out of 20), at least one child exhibited the same trait as a parent, indicating a consistent transmission pattern across generations. However, in 20% of families (4 out of 20), the trait skipped a generation.

Findings suggest that the absence of the palmaris longus muscle is a hereditary trait, occurring more frequently than its presence, within the studied families. The inheritance pattern aligns with an autosomal dominant transmission model. The absence of the palmaris longus muscle is likely influenced by a dominant gene exhibiting incomplete penetrance and variable expressivity, or potentially by mutational effects.