Inheritance & Family

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The body’s instructions for growth and development are packaged into 46 chromosomes or 23 pairs, from each parent. Chromosomes are further subdivided into smaller pieces of information called genes. Each gene provides the body with a specific set of instructions like a blueprint to build a protein, enzyme etc.

Chromosome pairs 1-22 are called Autosomes are and the same in biological male and females. The last pair of chromosomes are called the sex chromosomes X and Y. Biological females have 2 X chromosomes and 2 copies of the each of the genes located on the X chromosome. Biological males have an X and a Y chromosome. The X genes on the X and Y chromosomes are different. So biologic females have 2 copies of genes on the X chromosome and biological males have 1 copy of the genes located on the Y chromosome.

Each gene is made of DNA and has a sequence of chemical base pairs. If the DNA sequence has a difference this is called a variant. There are 3 types of variants Likely pathogenic (LP) or pathogenic (P): These variants have strong evidence and cause disease. LP/P variants were formerly called mutations. LP/P variants can be used to test other family members (called predictive genetic testing) to determine if they have inherited the HTAD condition.

Likely Benign (LB) or Benign (B): Much in the way that people’s appearance varies so can the sequence of our genes. There are many normal variations in a gene’s sequence that do not cause disease. These variants have strong evidence that the scientific community is certain that they do not cause disease.

Variants of unknown clinical significance (VUS): These variants do not have strong evidence to be certain that they cause disease. These variants are not used for family screening due to the uncertainty if their impact on health and HTAD. Over time the scientific community will learn more about VUSs and their classification may change to LP/P or LB/B.