(See also Overview of Chromosomal Anomalies Overview of Chromosomal Anomalies Chromosomal anomalies cause various disorders. Anomalies that affect autosomes (the 22 paired chromosomes that are alike in males and females) are more common than those that affect sex chromosomes... read more .)
Chromosomal deletion syndromes typically involve larger deletions that are usually visible on karyotyping. Syndromes involving smaller deletions (and additions) that affect one or more contiguous genes on a chromosome and are not visible on karyotyping are considered microdeletion and duplication syndromes Microdeletion and Microduplication Syndromes Microdeletion and microduplication syndromes are disorders caused by submicroscopic deletions or duplications of contiguous genes on particular parts of chromosomes. Postnatal diagnosis is suspected... read more . (See also Next-generation sequencing technologies Genetic Diagnostic Technologies Genetic diagnostic technology is rapidly improving. A small amount of DNA can be amplified using the polymerase chain reaction (PCR) process, which can produce millions of copies of a gene or... read more .)
5p- syndrome (5p minus syndrome or cri-du-chat syndrome)
Deletion of the end of the short arm of chromosome 5 (5p minus, usually paternal) is characterized by a high-pitched, mewing cry, closely resembling the cry of a kitten, which is typically heard in the immediate neonatal period, lasts several weeks, and then disappears. However, not all affected neonates have this unusual cry. Affected neonates are hypotonic and have low birth weight, microcephaly Microcephaly Microcephaly is a head circumference 2 standard deviations below the mean for age. (See also Introduction to Congenital Craniofacial and Musculoskeletal Disorders and Overview of Congenital... read more , a round face with wide-set eyes, downward slanting of the palpebral fissures (with or without epicanthal folds), strabismus Strabismus Strabismus is misalignment of the eyes, which causes deviation from the parallelism of normal gaze. Diagnosis is clinical, including observation of the corneal light reflex and use of a cover... read more , and a broad-based nose. The ears are low-set, abnormally shaped, and frequently have narrow external auditory canals and preauricular tags. Syndactyly Syndactyly Congenital limb defects involve missing, incomplete, supernumerary, or abnormally developed limbs present at birth. (See also Introduction to Congenital Craniofacial and Musculoskeletal Disorders... read more , hypertelorism Hypertelorism Eyes can be absent, deformed, or incompletely developed at birth. (See also Introduction to Congenital Craniofacial and Musculoskeletal Disorders and Overview of Congenital Craniofacial Abnormalities... read more , and cardiac anomalies Overview of Congenital Cardiovascular Anomalies Congenital heart disease is the most common congenital anomaly, occurring in almost 1% of live births (1). Among birth defects, congenital heart disease is the leading cause of infant mortality... read more occur often. Mental and physical development is markedly retarded. Many affected children survive into adulthood but have significant disability.
4p- syndrome (4p minus syndrome or Wolf-Hirschhorn syndrome)
Deletion of the short arm of chromosome 4 (4p) results in variable intellectual disability Intellectual Disability Intellectual disability is characterized by significantly subaverage intellectual functioning (often expressed as an intelligence quotient 70 to 75) combined with limitations of adaptive functioning... read more ; individuals with larger deletions are usually more severely affected. Manifestations also may include epilepsy, a broad or beaked nose, midline scalp defects, ptosis and colobomas Coloboma Eyes can be absent, deformed, or incompletely developed at birth. (See also Introduction to Congenital Craniofacial and Musculoskeletal Disorders and Overview of Congenital Craniofacial Abnormalities... read more , cleft palate Cleft Lip and Cleft Palate Cleft lip, cleft lip and palate, and isolated cleft palate, are collectively termed oral clefts (OCs). OCs are the most common congenital anomalies of the head and the neck with a total prevalence... read more , delayed bone development, and, in boys, hypospadias Hypospadias Congenital anomalies of the urethra in boys usually involve anatomic abnormalities of the penis and vice versa. In girls, urethral anomalies may exist without other external genital abnormalities... read more and cryptorchidism Cryptorchidism Cryptorchidism is failure of one or both testes to descend into the scrotum; in younger children, it is typically accompanied by inguinal hernia. Diagnosis is by testicular examination, sometimes... read more . Some patients with Wolf-Hirschhorn syndrome also have immune deficiency. Many affected children die during infancy; those who survive into their 20s often have severe disability.
These deletions may be visible on karyotyping but are also sometimes small and submicroscopic and may occur at either telomere (the end of a chromosome). Phenotypic changes may be subtle. Subtelomeric deletions may be associated with nonspecific intellectual disability and mildly dysmorphic features as well as multiple congenital anomalies.