10 Genetic Conditions Recognizable by Physical Features

7. Prader-Willi Syndrome - The Changing Physical Landscape

Prader-Willi syndrome, occurring in approximately 1 in 15,000 births, results from the loss of function of genes in the 15q11-q13 region and presents with physical features that evolve dramatically throughout different life stages. In infancy, affected individuals exhibit severe hypotonia (floppy baby syndrome) with feeding difficulties, failure to thrive, and characteristic facial features including a narrow forehead, almond-shaped eyes, and a thin upper lip with downturned corners of the mouth. The hands and feet are typically small, and cryptorchidism (undescended testes) is common in males. As children age, the clinical picture transforms remarkably, with hyperphagia (excessive eating) developing around age 2-5 years, leading to rapid weight gain and obesity if food intake is not carefully controlled. The facial features become more distinctive with age, showing a narrow face, small-appearing eyes due to periorbital fullness, and continued prominence of the thin upper lip. Short stature becomes apparent, and delayed or incomplete puberty occurs due to hypogonadism. The hands and feet remain characteristically small relative to body size, and scoliosis develops in approximately 80% of individuals. Behavioral characteristics include obsessive-compulsive tendencies, temper outbursts, and skin picking that can result in visible lesions and scarring. These dramatic phenotypic changes result from the complex genomic imprinting defects affecting multiple genes in the Prader-Willi critical region, demonstrating how genetic conditions can present with evolving physical manifestations that require different management strategies throughout the lifespan.