Chromosome 7, Partial Monosomy 7p is a rare chromosomal disorder characterized by deletion (monosomy) of a portion of the short arm (p) of chromosome 7 (7p). Associated symptoms and findings may be variable and may depend on the specific size and location of the deleted segment of 7p. However, in many cases, there is early closure of the fibrous joints (cranial sutures) between certain bones of the skull (craniosynostosis), resulting in an abnormally shaped head. For example, depending on the specific sutures involved, the forehead may appear unusually "triangular shaped" (trigonocephaly) or the head may seem abnormally long and narrow with the top pointed or conical (turricephaly). Affected infants and children may also have additional malformations of the skull and facial (craniofacial) region. Such abnormalities may include an unusually small head (microcephaly), closely or widely set eyes (ocular hypotelorism or hypertelorism), downslanting eyelid folds (palpebral fissures), and/or other findings.
Partial Monosomy 7p may also be characterized by additional physical features, such as growth deficiency, musculoskeletal abnormalities, genital defects, structural malformations of the heart that are present at birth (congenital heart defects), and/or other abnormalities. In addition, some affected individuals may have varying degrees of mental retardation and delays in the acquisition of skills requiring the coordination of mental and motor activities (psychomotor delays). Normal intelligence has also been reported.
In most cases, Chromosome 7, Partial Monosomy 7p appears to result from spontaneous (de novo) errors very early in embryonic development that occur for unknown reasons.
As noted above, the symptoms and physical findings associated with Chromosome 7, Partial Monosomy 7p may vary in range and severity from case to case. However, many affected individuals have growth delays before and after birth (prenatal and postnatal growth retardation). The syndrome may also be associated with varying degrees of psychomotor retardation and mental retardation; however, as noted earlier, some affected individuals may have normal intelligence.
Partial Monosomy 7p is also commonly characterized by premature closure of one or more fibrous joints (cranial sutures) between particular bones in the skull (craniosynostosis), potentially resulting in deformity of the skull and an unusually shaped head. The degree and severity of craniosynostosis may be variable, depending on the specific cranial sutures involved. For example, according to reports in the medical literature, Partial Monosomy 7p may be associated with various types of craniosynostosis, such as trigonocephaly or turricephaly. In trigonocephaly, early closure of the suture between bones forming the forehead (i.e., metopic suture) may cause the forehead to appear unusually narrow, pointed, and “triangular” or “keel shaped, with an abnormally decreased distance between the eyes (ocular hypotelorism). Turricephaly (also known as oxycephaly or acrocephaly) is characterized by premature fusion of the suture (i.e., coronal suture) between bones forming the forehead and the upper sides of the skull (frontal and parietal bones) and possibly other sutures, causing the head to appear unusually long and narrow, with the top conical or pointed. In addition, the back portion of the head (occiput) may appear flattened and the forehead unusually prominent. In some cases, other craniofacial features associated with variable craniosynostosis may include an unusually small head (microcephaly), widely spaced eyes (ocular hypertelorism), and/or other findings; the skull may also appear relatively dissimilar from one side to the other (cranial asymmetry).
In addition, in some instances, craniosynostosis, particularly that involving two or more cranial sutures, may lead to certain neurologic complications. Such complications may include hydrocephalus and abnormally increased pressure within the skull (intracranial pressure). Hydrocephalus is a condition in which obstructed flow or impaired absorption of cerebrospinal fluid (CSF) results in an abnormal accumulation of CSF, usually under increased pressure. CSF is the watery protective fluid that circulates through the cavities (ventricles) of the brain, the canal containing the spinal cord (spinal canal), and the space between layers of the protective membranes (meninges) surrounding the brain and spinal cord (i.e., subarachnoid space). Depending on the age at onset and other factors, associated symptoms may include sudden episodes of uncontrolled electrical activity in the brain (seizures), irritability, vomiting, headache, loss of coordination, deteriorating mental functioning, and/or other findings. In severe cases, potentially life-threatening complications may result.
In some affected individuals, Partial Monosomy 7p may be associated with additional craniofacial abnormalities. Such features may include downwardly slanting eyelid folds (palpebral fissures); vertical skin folds that may cover the eyes’ inner corners (epicanthal folds); drooping of the upper eyelids (ptosis); small, low-set, malformed (dysplastic) ears; a sunken nasal bridge (“saddle nose”); and/or other abnormalities.
In some instances, Partial Monosomy 7p may also be characterized by musculoskeletal abnormalities. Reported features have included permanent flexion of one or more fingers (camptodactyly); unusually short hands; abnormalities of the thumbs; a deformity in which the top part of the foot is elevated and the heel turned outward (“clubfoot” [i.e., talipes calcaneovalgus]); limited range of movement of certain joints; and/or other findings.
According to some reports, up to 50 percent of affected individuals may also have various congenital heart (cardiac) defects. Such cardiac defects may include an abnormal opening in the partition (septum) that separates the two lower chambers (ventricles) of the heart (ventricular septal defect [VSD]), an opening in the septum separating the two upper heart chambers (atrial septal defect), and/or other heart anomalies, allowing some oxygen-rich blood to recirculate through the lungs and potentially leading to rising blood pressure in the lungs (pulmonary hypertension). Associated symptoms and findings may vary, depending on the size, nature, and/or combination of heart malformations present and other factors. For example, in some cases, such as those with small isolated VSDs, no symptoms may be apparent (asymptomatic). However, in other instances, such as those with larger VSDs, associated symptoms and findings may include difficulties feeding, poor growth, difficult or labored breathing (dyspnea), profuse sweating, increased susceptibility to respiratory infections, impaired ability of the heart to pump blood efficiently to the lungs and the rest of the body (heart failure), enlargement of the heart, and/or other abnormalities. In severe cases, congenital heart disease may lead to potentially life-threatening complications.
Partial Monosomy 7p may also be characterized by additional physical features. Some affected individuals may have abnormal skin ridge patterns of the palms of the hands. Additional reported findings have included a highly arched roof of the mouth (palate) or incomplete closure (clefting) of the palate (cleft palate); retraction or downward displacement of the tongue (glossoptosis); underdevelopment (hypoplasia) of the external genitals; kidney (renal) defects, such as renal hypoplasia; an abnormally small colon (microcolon); and/or other defects.
In individuals with Chromosome 7, Partial Monosomy 7p, there is deletion (monosomy) of a portion of the short arm (p) of chromosome 7. Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as “p,” a long arm identified by the letter “q,” and a narrowed region at which the two arms are joined (centromere). Chromosomes are further subdivided into bands that are numbered outward from the centromere. For example, the short arm of chromosome 7 (7p) includes bands 7p11-p15 and bands 7p21-p22; the end or “terminal” of 7p is known as “7pter.”
According to reports in the medical literature, there is significant variation in the size and location of the deleted segment of 7p, potentially affecting the range and severity of associated symptoms and findings. Reported cases have included variable “distal” deletions extending to the terminal band (e.g., from 7p13-pter to 7p21p22-pter) and various “interstitial” deletions (e.g., from 7p13 or 7p15 to 7p21). (“Distal” indicates away or farthest from a particular point of reference, meaning the chromosome’s centromere; “interstitial” means situated between, such as between other regions of a chromosome.) According to some investigators, evidence suggests that craniosynostosis in association with Partial Monosomy 7p appears to be due to partial or complete deletion of 7p21-p22 or, more rarely, monosomy of 7p13-p14. Further research is needed to learn more about the specific region(s) that may be responsible for expression of characteristic symptoms and findings in those with the chromosomal syndrome.
In most cases, Chromosome 7, Partial Monosomy 7p appears to be caused by spontaneous (de novo) errors during early embryonic development that occur for unknown reasons. In such instances, the parents of the affected child usually have normal chromosomes and a relatively low risk of having another child with the chromosomal abnormality.
Rare cases have also been reported that appear to result from balanced chromosomal rearrangements in one of the parents. If a chromosomal rearrangement is balanced, meaning that it consists of an altered but balanced set of chromosomes, it is usually harmless to the carrier. However, such a chromosomal rearrangement may be associated with an increased risk of abnormal chromosomal development in the carrier’s offspring.
Chromosomal analysis and genetic counseling are typically recommended for parents of an affected child to help confirm or exclude the presence of a balanced chromosomal rearrangement involving chromosome 7 in one of the parents.
Chromosome 7, Partial Monosomy 7p is a rare chromosomal disorder that appears to affect males and females in relatively equal numbers. More than 30 cases have been reported in the medical literature.
In some cases, the diagnosis of Chromosome 7, Partial Monosomy 7p may be suggested before birth (prenatally) by specialized tests such as ultrasound, amniocentesis, and/or chorionic villus sampling (CVS). During fetal ultrasonography, reflected sound waves create an image of the developing fetus, potentially revealing certain characteristic findings that suggest a chromosomal disorder or other abnormalities. With amniocentesis, a sample of fluid that surrounds the developing fetus is removed and analyzed, while CVS involves the removal of tissue samples from a portion of the placenta. Chromosomal analysis performed on such fluid or tissue samples may reveal the presence of Partial Monosomy 7p.
The syndrome may be diagnosed and/or confirmed after birth (postnatally) by a thorough clinical evaluation, identification of characteristic physical findings, and chromosomal analysis. Diagnostic evaluation may include various studies, including advanced imaging techniques, to help detect and/or characterize certain abnormalities that may be associated with the syndrome (e.g., particular craniofacial defects, musculoskeletal abnormalities, etc.). In addition, a thorough cardiac evaluation may be advised to detect any heart abnormalities that may be present. Such evaluation may include a thorough clinical examination, evaluation of heart and lung sounds through use of a stethoscope, and specialized tests that enable physicians to evaluate the structure and function of the heart (e.g., x-ray studies, electrocardiography [EKG], echocardiography).
The treatment of Chromosome 7, Partial Monosomy 7p is directed toward the specific symptoms that are apparent in each individual. Such treatment may require the coordinated efforts of a team of medical professionals, such as pediatricians; surgeons; physicians who diagnose and treat disorders of the skeleton, joints, muscles, and related tissues (orthopedists); heart specialists (cardiologists); physicians who diagnose and treat neurologic disorders (neurologists); and/or other health care professionals.
For affected infants with craniosynostosis, depending on the number and type of cranial suture(s) involved and other factors, early surgery may be advised to help prevent abnormal shaping of the head, increase skull capacity, and/or prevent possible neurologic complications. Surgery may also be recommended for certain additional craniofacial malformations, musculoskeletal defects, and/or other physical abnormalities associated with the syndrome. In addition, for those with congenital heart defects, treatment may require the administration of certain medications, surgical intervention, and/or other measures. Surgical procedures performed will depend on the size, nature, severity, and combination of anatomical abnormalities, their associated symptoms, and other factors.
Early intervention services may also be important in ensuring that affected children reach their potential. Special services that may be beneficial include special remedial education, physical therapy, and/or other medical, social, and/or vocational services. Genetic counseling will also be of benefit for affected individuals and their families. Other treatment for this disorder is symptomatic and supportive.
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