Lecture 4

Recurrent chromosome abnormalities

Includes duplication and deletion syndromes, are caused by recombination at segmental duplications and non-allelic homologous recombination (NAHR), leading to copy number variation.

Nonrecurrent chromosome abnormalities

Genetic disorders caused by duplications or deletions with variable breakpoints; origins are not well understood.

Uniparental disomy

When an individual inherits both homologues from a single parent, often caused by nondisjunction during meiosis and mitosis.

Isodisomy

The inheritance of two copies of the same homologue from one parent, which can lead to a recessive disorder if the parent is a carrier.

Heterodisomy

The inheritance of one copy of each homologue from one parent.

Charcot-Marie Tooth Disease Type 1A (CMT1A)

An autosomal dominant peripheral neuropathy characterized by progressive weakness and atrophy of leg muscles, usually caused by increased dosage of the PMP22 gene on chromosome 17.

Hereditary Neuropathy with Liability to Pressure Palsies (HNPP)

An autosomal dominant demyelination disorder characterized by focal pressure neuropathies (numbness and tingling when pressure is applied) and peroneal palsy with foot drop, usually due to decreased dosage of the PMP22 gene on chromosome 17.

Segmental Duplication

Long DNA sequences that are repeated in a genome and can cause deletions or duplications if paired accidentally, characterized by a high level of sequence identity.

Contiguous Gene Syndromes

Genetic disorders caused by changes in the dosage of multiple adjacent genes.

Cri du chat syndrome

A genetic disorder characterized by a crying sound resembling a cat's meow, distinct facial features, variable levels of mental retardation, and speech defects, often due to haploinsufficiency of genes in chromosome band 5p, with critical region 5p15 missing in all patients.