What Happens When the Brain Can’t Tell You to Stop Eating?

What if your child never felt full, no matter how much they ate?

That’s the reality for many families living with Prader-Willi Syndrome (PWS) member, a rare genetic disorder that affects roughly 1 in 15,000 births. It starts quietly—maybe with a baby who’s too sleepy to eat or too weak to cry—and then shifts into something far more challenging as they grow. They are navigating childhood, not just with developmental delays or behavioral outbursts, but with an insatiable hunger that can lead to life-threatening complications if not carefully managed.

PWS affects hormones, growth, emotions, and nearly every aspect of daily life—for both the child and their family. And while it’s complex, it’s not hopeless. With the right information, routines, and support, families can and do carve out healthy, fulfilling lives.

What’s Genetically Wrong in PWS?

PWS is a rare genetic disorder, but not one that typically runs in families. Instead, it’s caused by a specific error on chromosome 15 that happens around conception or early in fetal development.

In most people, a set of genes on chromosome 15 from the father is active and plays a key role in regulating hunger and metabolism. The same genes from the mother are naturally inactive. In PWS, the problem is that the father’s copy of these genes is missing or turned off, and the mother’s copy can’t step in to help.

There are three main ways this can happen.

1. Deletion is the most common cause. A chunk of the father’s chromosome 15 is missing. Without these genes, the brain doesn’t get the signals it needs to regulate hunger and fullness properly.
2. Another one is maternal uniparental disomy (UPD) and in about 25% of cases, the child ends up with two copies of chromosome 15 from the mother and none from the father. Since the maternal genes in this region are naturally silent, the child has no working copy of the key genes.
3. Lastly, in the imprinting defects, which are rare cases, the father’s chromosome is present, but a small glitch in a control area called the imprinting center causes his genes to behave like the mother’s—silent and inactive.

All three lead to the same outcome: the brain doesn't receive the right genetic instructions to manage appetite, growth, and development—hallmarks of Prader-Willi Syndrome.

How PWS Shows Up Over Time

PWS shows up differently from person to person, but most signs fall into two main categories: physical symptoms and behavioral or developmental challenges. Many start in infancy and evolve as the child grows.

Early Signs in Infancy

Babies with PWS often show clear signs early on, such as:

• Weak or quiet cry
• Low muscle tone (they may feel floppy when held)
• Poor feeding and trouble gaining weight
• Sleepiness or lack of energy

These early difficulties can make feeding and growth a challenge in the first few months.

Physical Features That Appear Over Time

As children grow, other physical traits may become more noticeable:

• Almond-shaped eyes
• A long, narrow head shape
• A small, downturned mouth (sometimes described as triangular)
• Short height
• Small hands and feet
• Underdeveloped genitals

These signs may not be obvious at birth but typically become more apparent in early childhood.

Behavioral and Developmental Challenges

Children and adults with PWS often face a range of cognitive and behavioral symptoms, such as:

• Intellectual delays or learning difficulties
• Emotional outbursts, temper tantrums, or stubbornness
• Obsessive or compulsive habits, like skin picking
• Trouble with sleep regulation
• Food-related issues, especially hyperphagia—an intense, constant hunger that doesn’t go away after eating

Hyperphagia is one of the hallmark symptoms of PWS. It often leads to severe obesity, which can trigger serious health problems like type 2 diabetes, heart disease, and sleep apnea if not managed.

Finding Balance When Caring for Someone with PWS

Raising a child with PWS is hard—there’s no way around it. Between managing meals, monitoring behavior, juggling doctor visits, and trying to keep things “normal” at home, it can feel like your whole world revolves around staying one step ahead. It’s a lot. And it’s okay to say that.

The Takeaway

Being aware of this condition means recognizing how deeply it can affect everyday life, and how much can be done with the right tools. From early signs to lifelong challenges, each stage brings new needs—and new opportunities to support growth, safety, and quality of life. While the road may be tough, knowledge, structure, and community make a real difference. Keep learning, keep advocating, and never underestimate the power of informed care.