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Syndromes of chromosomal deletions
Last reviewed: 23.04.2024
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Syndromes of chromosomal deletions are a consequence of the loss of a part of the chromosome. At the same time there is a tendency to develop severe congenital malformations and a significant delay in mental and physical development. Syndromes of chromosomal deletions are rarely supposed to be prenatal, but sometimes they can be diagnosed during this period, if for some reasons (not associated with these syndromes) they carry out karyotyping. Postnatal suspicion of chromosomal deletions syndromes in the appearance of the child, clinical manifestations and confirmed by karyotype research, as well as other methods of genetic analysis.
5p-Deletion (cat-scream syndrome)
The deletion of the terminal portion of the short arm of the 5th chromosome (5p) is characterized by a high, thin, meowing cry, very reminiscent of the kitten's cry, which occurs immediately after birth for several weeks, and then disappears. A child is born with low body weight, hypotension, he has microcephaly, a round face with widely spaced eyes, obliquely located (downward) eye slits (with or without epicenta), strabismus and a nose with a wide base. The ears are located low, anomalous, before they can be marked outgrowths, the external auditory canal is often narrowed. Syndactyly, hypertelorism and heart defects are often observed. There is a marked delay in mental and physical development. Many patients live more than 20 years, but are deeply disabled.
[1]
4p-Deletion (Wolff-Hirschhorn Syndrome)
Deletion of the short arm of the fourth chromosome (4p) leads to deep mental retardation. Manifestations may also include a broad or beak-like nose, midline head skin defects, ptosis, colobomas, cleft palate, later maturation of bone tissue, as well as in boys hypospadias and cryptorchidism. Many patients die in the first year of life; relatively few live more than 20 years, but are deeply disabled and prone to infections and epilepsy.
[2], [3], [4], [5], [6], [7], [8], [9], [10], [11]
Syndromes of linked genes
These syndromes include micro and submicroscopic deletions of linked genes in certain parts of many chromosomes; There are also small duplications of chromosomes. The effects of duplications are usually easier than fission. Almost all cases are sporadic; at the same time, with mild lesions, such as, for example, with some 22q11.21 deletions, patients can transmit the syndrome by inheritance. Numerous syndromes with widely varying manifestations were identified. Deletions and duplications are often detected using fluorescent probes and other methods. Sometimes deletions and duplications can not be detected by cytogenetic methods, but their presence can be confirmed with DNA probes complementary to the missing region.
Telomere deletions
These are small and often submicroscopic deletions that can occur at either end of the chromosome. Phenotypic changes can be minimal. Telomeric deletions can constitute a large percentage of nonspecific mental retardation, in which the patient has slightly dysmorphic features.