2025 – PAGE 264 – GENETICS & INHERITED DISEASES

2025 – Core Study Guide 14 – Genetics and Inherited Diseases 2025 – PAGE 264 – GENETICS & INHERITED DISEASES

TRISOMY 18 (AKA EDWARDS SYNDROME)

Trisomy 18 (AKA Edwards syndrome) findings include rocker-bottom feet (rounded, rocking-chair like plantar surface), clenched fists with overlapping fingers, underdeveloped/hypoplastic nails, horseshoe kidneys, crossed legs, small jaw (micrognathia), prominent occiput, and pectus excavatum. Patients can also have cardiac defects such as an ASD or VSD. Patients with Trisomy 18 have a horrible prognosis: most die in utero or by the age of one year.

IMAGE: www.pbrlinks.com/TRISOMY18-1
IMAGE: www.pbrlinks.com/TRISOMY18-2

MNEMONIC: Imagine an 18-year-old named Ed who is dressed in a red, white, and blue suit for his birthday party. He’s feeling so patriotic because he can finally vote! He jumps onto and stands on a ROCKING chair that has legs that look like HORSESHOE KIDNEYS. He gives a thank-you speech. At the end he throws his right hand up in the air like a ROCKER with a CLENCHED FIST AND OVERLAPPING FINGERS three times as he says, “Thank you! Thank you! Thank you!” It’s a little shaky up there on the ROCKING chair and he falls. As he falls, he hits his CHEST on an arm of the chair, and as he tries to brace himself, his CLENCHED FIST gets run over by the HORSESHOE-KIDNEY-shaped legs and HIS FINGERNAILS ARE CRUSHED.

MNEMONIC: Imagine “FrEDDIE Mercury,” a rockstar with ROCKER BOTTOM feet, CLENCHING his fist while singing with his HORSESHOE-shaped mustache draped over a mic (www.pbrlinks.com/FREDDIE).

TRISOMY 13 (AKA PATAU SYNDROME)

Trisomy 13 (AKA Patau syndrome) findings include cardiac defects, cleft lip ± palate, punched out scalp lesions, polydactyly, low-set ears, cystic kidneys, microcephaly, and microphthalmia. Patients with Patau syndrome have a poor prognosis: most die by 6 months of age.

IMAGE: www.pbrlinks.com/TRISOMY13-1

PEARL: Likely a low-yield disorder. Move on if you find yourself spending too much time here.

MNEMONIC: Imagine JASON from FRIDAY THE 13TH wearing his hockey mask to cover up his CLEFT LIP. Note that it has PUNCHED OUT LESIONS on it. In one hand he has a sword, and the other hand has “EXTRA FINGERS.” See the image below for this visual pun – www.pbrlinks.com/TRISOMY13-2

MISCELLANEOUS GENETIC FINDINGS & DISORDERS

NOTE: This section includes disorders without an established inheritance pattern or genetic etiology.

TERMINOLOGY

  • SYNDACTYLY: Fusion of two or more fingers. This may also include fusion of bones.
  • CLINODACTYLY: Permanent deviation of one or more fingers.

CLEFT DISORDERS

Cleft disorders are multifactorial conditions, which means that there is a significant chance of recurrence in future pregnancies (about 5%). Multifactorial conditions are frequently associated with other anomalies.

IMAGE: www.pbrlinks.com/CLEFTDISORDER1

  • CLEFT PALATE: A child born with a CLEFT PALATE is much more likely to have other anomalies than a child born with only a cleft lip. These patients are also more likely to have an underlying chromosomal anomaly than a cleft lip patient OR even a cleft palate with a cleft lip patient. So, get a karyotype! There is a high risk of recurrence, HIGH risk of associated anomalies, and HIGH risk of an associated chromosomal defect so GET A KARYOTYPE.
  • CLEFT LIP WITH OR WITHOUT CLEFT PALATE: There is a high risk of recurrence, low risk of associated anomalies and a low risk of an associated chromosomal defect.
  • DISEASE ASSOCIATIONS: Cleft lips and/or palate are associated with various disorders including Treacher Collins Syndrome, DiGeorge Syndrome, Crouzon Syndrome, Apert Syndrome, Pierre-Robin Syndrome and Trisomy 13.
    • MNEMONIC: Imagine that a PINK PLATE represents any sort of cleft deformity. This has been chosen because lips and palates are pink, and “plate” looks/sounds like palate. Here’s the story: Your favorite TREACHER loves animals and the color pink. She’s wearing a pink dress as she walks out of her classroom with a PINK PLATE filled with CROUTONS and PEARS. As soon as she puts the plate down, a ROBIN flies over, and a CURIOUS MONKEY (named Curious George) shuffles over to eat the yummy food on the PINK PLATE.
    • KEY: TREACHER Collins, Crouzon (CROUTONS), Apert (PEARS), Pierre-Robin (ROBIN) and DiGeorge (CURIOUS GEORGE).
  • SUBMUCOUS CLEFT PALATE

These are difficult to see because they are covered by a layer of normal-looking mucosa, so look for a BIFID UVULA. Patients can have hearing deficits due to problems with tympanic membrane mobility, so obtain tympanometry. If the patient has difficulty forming certain words after the age of 5, surgically repair.

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