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Related Concept Videos

Pedigree Analysis01:35

Pedigree Analysis

Overview
Epistasis01:39

Epistasis

In addition to multiple alleles at the same locus influencing traits, numerous genes or alleles at different locations may interact and influence phenotypes in a phenomenon called epistasis. For example, rabbit fur can be black or brown depending on whether the animal is homozygous dominant or heterozygous at a TYRP1 locus. However, if the rabbit is also homozygous recessive at a locus on the tyrosinase gene (TYR), it will have an unshaded coat that appears white, regardless of its TYRP1...
Pleiotropy01:33

Pleiotropy

Pleiotropy is the phenomenon in which a single gene impacts multiple, seemingly unrelated phenotypic traits. For example, defects in the SOX10 gene cause Waardenburg Syndrome Type 4, or WS4, which can cause defects in pigmentation, hearing impairments, and an absence of intestinal contractions necessary for elimination. This diversity of phenotypes results from the expression pattern of SOX10 in early embryonic and fetal development. SOX10 is found in neural crest cells that form melanocytes,...
Pharmacogenetic Phenotypes: Alterations in Pharmacokinetics, Drug Targets and Biologic Milieu01:29

Pharmacogenetic Phenotypes: Alterations in Pharmacokinetics, Drug Targets and Biologic Milieu

Genetic variations significantly influence drug response through pharmacokinetics, receptor interactions, and biologic milieu modifications. Pharmacokinetic alterations impact drug metabolism and clearance, affecting efficacy and toxicity. Variants in drug-metabolizing enzymes, such as CYP2C9 and CYP2C19, alter drug activation and elimination. For example, CYP2C9 loss-of-function variants require lower warfarin doses to prevent excessive bleeding, while CYP2C19 variants reduce clopidogrel...
Trihybrid Crosses02:27

Trihybrid Crosses

Trihybrid Crosses
Some of Mendel’s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A trihybrid cross is a combination of three individual monohybrid crosses. For example, plant height (tall vs. short), seed shape (round vs. wrinkled), and seed color (yellow vs. green).
The F1 generation plants of a trihybrid cross are heterozygous for all three traits and produce eight gametes. Upon self-fertilization, these gametes have an equal chance to...
Genetic Lingo01:11

Genetic Lingo

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Related Experiment Video

Updated: Jul 8, 2026

Navigating MARRVEL, a Web-Based Tool that Integrates Human Genomics and Model Organism Genetics Information
09:37

Navigating MARRVEL, a Web-Based Tool that Integrates Human Genomics and Model Organism Genetics Information

Published on: August 15, 2019

Intrafamilial phenotypic variability in tuberous sclerosis complex.

David A Lyczkowski1, Kerry D Conant, Margaret B Pulsifer

  • 1Department of Neurology, Massachusetts General Hospital, Boston, USA.

Journal of Child Neurology
|January 5, 2008
PubMed
Summary

Tuberous sclerosis complex (TSC) shows significant variation in symptoms, even between identical twins. This phenotypic diversity in TSC highlights the importance of genetic counseling for families.

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In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila
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In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila

Published on: August 20, 2019

Area of Science:

  • Genetics
  • Neurology
  • Medical Genetics

Background:

  • Tuberous sclerosis complex (TSC) is a genetic disorder characterized by hamartoma formation in multiple organs.
  • Significant phenotypic variability is observed in TSC, complicating diagnosis and management.
  • Understanding intrafamilial variation is crucial for predicting disease course and providing genetic counseling.

Purpose of the Study:

  • To retrospectively assess clinical manifestations of tuberous sclerosis complex (TSC) within families.
  • To investigate the extent of interfamilial and intrafamilial phenotypic variation in TSC.
  • To explore potential factors contributing to phenotypic diversity in TSC.

Main Methods:

  • Retrospective clinical assessment of 5 families with TSC.
  • Inclusion of a pair of monozygotic twins to evaluate intrafamilial variability.
  • Analysis of tuber count, epilepsy severity, cognitive profiles, and organ-specific findings.

Main Results:

  • Interfamilial variation in tuber count was greater than intrafamilial variation.
  • Epilepsy severity and cognitive profiles varied significantly within and between families, notably in monozygotic twins.
  • IQ showed an inverse relationship with tuber count.
  • Cutaneous, renal, and cardiac findings did not exhibit clear familial clustering.
  • Monzygotic twins with similar physical manifestations displayed distinct neurocognitive profiles.

Conclusions:

  • Phenotypic variation in TSC may stem from random second-hit events or unidentified genetic modifiers.
  • Significant intrafamilial variability, even in monozygotic twins, underscores the complexity of TSC.
  • Familial variation in TSC phenotype has critical implications for genetic counseling and patient management.