2025 – PAGE 267 – GENETICS & INHERITED DISEASES

PRADER-WILLI SYNDROME (AKA PRADER WILLI SYNDROME)

Prader-Willi syndrome (AKA Prader Willi syndrome) patients can have hypotonia (floppy baby), mild intellectual disability, almond-shaped eyes (often with mild strabismus), small hands, a HUGE appetite, obesity, and small testicles/penis in boys.

• PEARLS: Like Angelman’s, it can be found in BOYS or GIRLS. This mechanism of this disorder is the mirror image of that of Angelman’s. It occurs due to the absence or dysfunction of the PATERNAL copy of a gene in the same region of chromosome 15 as in Angelman syndrome. It also occurs when two maternal copies of chromosome 15 were received and no paternal copies (maternal disomy), and also when a mutation of the paternal gene makes it behave like the MATERNAL gene (called maternal imprinting). Symptoms are much milder in females. The gene location is probably not important for the test, but the fact that it is KNOWN (15q11-13) means that this disorder can be diagnosed by FISH.
  • IMAGE: www.pbrlinks.com/PRADERWILLI1
  • IMAGE: www.pbrlinks.com/PRADERWILLI2
  • MNEMONIC: Imagine a FAT Will Smith with TINY HANDS shoving tons of ALMONDS in his mouth. He’s wearing a t-shirt that says, “MOMMY’S LITTLE FATTY.”
    • KEY: ALMONDS represent the shape of the eyes, and the t-shirt represents maternal imprinting.
  • MNEMONIC: Sorry, this is a good mnemonic but not politically correct. Imagine a HUGE, OBESE, and DUMB FISH/WHALE named FREE WILLY with such a SMALL PENIS that you can hardly see it. It’s so DUMB that it tried to jump over a dock, but ended up landing on it instead. Now this big DUMB FISH is stuck on the dock. He’s HUNGRY. He’s thrashing back and forth, and he’s FLOPPING his tiny WILLY all around.
  • MNEMONIC IMAGE: www.pbrlinks.com/PRADERWILLI3
    • KEY: FISH represents the mode of diagnosis, HUGE/OBESE represents obesity, DUMB represents intellectual disability, HUNGRY represents the insatiable appetite, and FLOPPING represents the hypotonia. In this mnemonic, you could also make Willy’s eyes almond shaped and imagine that he has small fins.

LAURENCE-MOON SYNDROME

Laurence-Moon Syndrome is a rare condition similar to Prader Willi, but it is PROGRESSIVE. It is associated with consanguineous marriages. It involves the eyes, the brain, and the endocrine system. It is associated with intellectual disability, retinitis pigmentosa, hypogonadism and spastic paraplegia.

MNEMONIC: Rename it “insurance mOoOn.” The two capital “O’s” look like EYES and bOObs. The lower case “o” represents a small brain to help you remember that there are PROGRESSIVE CNS issues. INSURANCE kind of sounds like Laurence, and may help you think of PROGRESSIVE INSURANCE!

MNEMONIC: LMS stands for Laurence-Moon Syndrome. Or, maybe it stands for, I Like My Sibling (consanguineous marriages).