Information on the following diseases can be found in the Related Disorders section of this report:

• Chromosome 22, Monosomy 22q
• Chromosomal Disorders (General)

As mentioned earlier, the symptoms and physical findings associated with Chromosome 10, Monosomy 10p may vary in range and severity from case to case. However, according to reports in the medical literature, most individuals with the disorder are affected by severe mental retardation and delays in the acquisition of skills requiring the coordination of mental and motor activities (psychomotor retardation). Monosomy 10p is also frequently associated with growth delays after birth, resulting in short stature.

Affected infants and children also typically have certain distinctive abnormalities of the skull and facial (craniofacial) region. Such malformations may include an abnormally small head (microcephaly) with a protruding forehead (frontal bossing); a small jaw (micrognathia); a low nasal bridge and upturned (anteverted) nostrils; malformed, low set ears; and a short neck. Additional craniofacial defects may also be present, such as widely spaced eyes (ocular hypertelorism); short, downwardly slanting eyelid folds (palpebral fissures); vertical skin folds covering the eyes' inner corners (epicanthal folds); drooping of the upper eyelids (ptosis); and abnormal deviation of one eye in relation to the other (strabismus). Less commonly, the disorder may be associated with incomplete closure of the roof of the mouth (cleft palate) and an abnormal groove in the upper lip (cleft lip).

Individuals with Monosomy 10p may also have widely spaced nipples; foot malformations; and/or structural defects of the heart (congenital heart defects). In addition, the disorder may be associated with abnormalities of the urinary tract and the genitals, such as undescended testes (cryptorchidism) and an underdeveloped (hypoplastic) scrotum in affected males. Some individuals may also have dysfunction of the lowest region of the brain known as the brainstem, which helps to convey messages traveling between other brain regions and the spinal cord and has sensory, motor, and reflex functions. In individuals with Monosomy 10p, brainstem dysfunction may be associated with severe hearing loss due to impaired conversion of sound vibrations and failed transmission of nerve impulses from the inner ear via the auditory nerve to the brain (i.e., sensorineural hearing loss).

As mentioned previously, Monosomy 10p may often be associated with features of DiGeorge syndrome (DGS). DGS is a congenital disorder resulting from improper development of embryonic structures that form the thymus and parathyroid glands. Other embryonic structures that develop at about the same time may also sometimes be affected, potentially leading to certain defects of the heart and its major blood vessels (cardiovascular defects) and/or craniofacial malformations. The thymus is thought to play a crucial role in the body's immune system beginning during fetal development until about puberty. It serves to promote the maturation of certain precursor* cells into T lymphocytes, which are specialized white blood cells that assist in the recognition or destruction of foreign proteins (antigens), such as certain invading microorganisms. (*A precursor is a biological forerunner or a substance that precedes and is the source of another, typically more mature or active substance.) The parathyroid glands are two pairs of relatively small glands that produce parathyroid hormone, which helps to regulate blood calcium levels.

Individuals with Monosomy 10p who have features of DGS typically have variable degrees of hypoplasia or underdevelopment of the thymus and parathyroid glands. This is sometimes referred to as "partial DiGeorge syndrome." Hypoplasia of the thymus may lead to deficient activity of the immune system and impaired resistance to certain viral, bacterial, or fungal infections. In other cases, however, some individuals with partial DiGeorge syndrome may not appear to have an increased susceptibility to recurrent infections.

In those with hypoplasia of the parathyroid glands, deficient secretion of parathyroid hormone (hypoparathyroidism) may lead to low calcium blood levels (hypocalcemia) and associated findings during the first days of life (neonatal tetany). Such features may include muscle cramping and spasms, convulsions, tremors, spasmodic closure of the larynx (laryngospasm), and/or other findings.

Cardiovascular abnormalities that have been reported in association with DGS include defects of the aorta or the major artery that supplies oxygenated blood to most of the body; an abnormal opening in the fibrous partition (septum) that separates the lower or upper chambers of the heart (ventricular or atrial septal defects); and/or other congenital defects.

Experts suggest that certain abnormalities frequently seen in individuals with Monosomy 10p may be absent in those with classic DiGeorge syndrome (i.e., DGS that results from minute deletions of material from the long arm of chromosome 22). For example, severe mental retardation and growth delays are seen in most individuals with Monosomy 10p yet may not be apparent in those with classic DGS. Sensorineural deafness, a finding reported in a number of individuals with Monosomy 10p, has not been associated with classic DGS. In addition, abnormalities of the heart and its major blood vessels are more frequent in classic DGS than Monosomy 10p. (For further information, please see the "Causes" section of this report below.)
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Chromosome 10, Monosomy 10p is a rare chromosomal abnormality in which there is deletion (monosomy) of the end (distal) portion of the short arm (p) of chromosome 10. 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" and a long arm identified by the letter "q." Chromosomes are further subdivided into bands that are numbered.

In individuals with Monosomy 10p, the range and severity of associated symptoms and findings may vary, depending upon the exact length or location of the deleted portion of chromosome 10p. In some cases, Monosomy 10p appears to occur spontaneously (de novo) for unknown reasons very early in embryonic development. The parents of a child with a "de novo" deletion usually have normal chromosomes and a relatively low risk of having another child with the chromosomal abnormality. In other cases, Monosomy 10p may result from a translocation involving chromosome 10p and another chromosome or chromosomes. Translocations occur when regions of certain chromosomes break off and are rearranged, resulting in shifting of genetic material and an altered set of chromosomes. Such translocations may occur spontaneously for unknown reasons (de novo) or be transmitted by a parent who is a carrier of a "balanced" translocation. (If a chromosomal rearrangement is balanced--i.e., 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 may determine whether a parent has a balanced translocation.)

As mentioned above, Monosomy 10p may often be associated with features of DiGeorge syndrome (DGS), a condition caused by abnormal development of embryonic structures that form the thymus and parathyroid glands and, in some instances, other embryonic structures. DGS most commonly results from spontaneous (sporadic), minute deletions (microdeletions) of material from the long arm (q) of chromosome 22 (22q11.2 [known as the "DiGeorge syndrome chromosomal region" or "DGCR"). Such cases are sometimes referred to as "classical DiGeorge syndrome." However, the condition may also have other underlying causes, such as various chromosomal abnormalities, including Monosomy 10p or an interstitial deletion of the long arm of chromosome 22 (Chromosome 22, Deletion 22q11.2), and fetal exposure to alcohol or certain vitamin A-like compounds (retinoids) during pregnancy. (For further information on classic DiGeorge syndrome, please use "DiGeorge" as your search term in the Rare Disease Database. For more on Chromosome 22, Deletion 22q11.2, please see the "Related Disorders" section below.)
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Chromosome 10, Monosomy 10p is typically evident at birth (congenital). Since the disorder was originally reported in the medical literature in 1970, over 35 cases have been recorded. In such observed cases, males appear to be more frequently affected than females.
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Symptoms of the following disorders may also be similar to those of Chromosome 10, Monosomy 10p. Comparisons may be useful for a differential diagnosis:

Chromosome 22, Deletion 22q11.2 is a rare chromosomal disorder in which there is deletion of the long arm of chromosome 22. Individuals with deletions involving band q11.2 (i.e., DGCR) are affected by DiGeorge syndrome, including underdevelopment or absence of the thymus and potentially increased susceptibility to certain infections; hypoparathyroidism; and, in some cases, cardiovascular defects. Deletions that involve the end (distal) portion of chromosome 22q may also be associated with severe mental and psychomotor retardation; poor muscle tone (hypotonia); characteristic craniofacial features; and skeletal defects. Craniofacial abnormalities may include an abnormally small head (microcephaly); deeply set eyes; vertical skin folds that cover the eyes' inner corners (epicanthal folds); low, full eyebrows and long eyelashes; a broad, bulbous nose; and an abnormally long vertical groove in the center of the upper lip (philtrum). Affected individuals may also have abnormal front-to-back curvature of the spine (kyphosis), unusually short fingers, and/or other abnormalities. This syndrome may appear to occur spontaneously (de novo) for unknown reasons or result from a parental balanced translocation involving chromosome 22q and another chromosome.

Additional chromosomal disorders may have features similar to those associated with Chromosome 10, Monosomy 10p. Chromosomal testing is necessary to confirm the specific chromosomal abnormality present. (For further information on such disorders, choose the name of the specific chromosomal disorder in question or use "chromosome" as your search term in the Rare Disease Database.)
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Diagnosis
In some cases, a diagnosis of Chromosome 10, Monosomy 10p may be suggested before birth (prenatally) by tests such as amniocentesis or chorionic villus sampling (CVS). During amniocentesis, a sample of fluid that surrounds the developing fetus is removed and analyzed. CVS involves the removal of tissue samples from a portion of the placenta. Chromosomal analysis performed on the fluid or tissue samples may reveal the presence of Monosomy 10p.

Chromosome 10, Monosomy 10p may also be diagnosed or confirmed after birth based upon a thorough clinical evaluation, detection of characteristic physical findings, and chromosomal analysis. Specialized tests may also be conducted to help detect and/or characterize certain abnormalities that may be associated with the disorder. These may include tests to assess blood calcium levels; immunologic studies; advanced imaging techniques to confirm or characterize abnormalities of the thymus, parathyroid glands, and brain (e.g., ultrasonography, computed tomography [CT] scanning, magnetic resonance imaging [MRI]); and studies to evaluate the structure and function of the heart (e.g., x-ray imaging, electrocardiogram [EKG], echocardiogram, cardiac catheterization). Testing known as brainstem auditory evoked response (BAER) may also be conducted to screen affected infants for hearing impairment. During BAER, clicking sounds are used and responses are recorded to evaluate hearing (auditory) pathways of the brainstem. In some cases, additional diagnostic studies may also be recommended.

Treatment
The treatment of Chromosome 10, Monosomy 10p 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; specialists in the functioning of the immune system (immunologists); endocrine disorder specialists (endocrinologists); physicians who diagnose and treat heart abnormalities (cardiologists); hearing specialists; and/or other health care professionals.

The treatment of affected individuals is symptomatic and supportive. For those with hypoparathyroidism, treatment may include administration of calcium and vitamin D, which aids in calcium absorption. For individuals with an increased susceptibility to recurrent infections, the use of particular antibiotic, antiviral, and antifungal medications and other agents may be required to help prevent and aggressively treat certain infections. (For further information on disease management for features of DiGeorge syndrome, please choose "DiGeorge" as your search term in the Rare Disease Database.)

Physicians may also recommend corrective surgery for certain craniofacial and/or other malformations potentially associated with Monosomy 10p. In addition, for those with congenital heart defects, treatment with certain medications, surgical intervention, and/or other measures may be necessary. The specific surgical procedures performed will depend upon the severity and location of the anatomical abnormalities, their associated symptoms, and other factors.

Early intervention may be important in ensuring that affected children reach their potential. Special services that may be beneficial include special education, physical therapy, and/or other medical, social, and/or vocational services. Genetic counseling will also be of benefit for families of affected children. Other treatment for this disorder is symptomatic and supportive.
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Online Mendelian Inheritance in Man, OMIM (TM). John Hopkins University, Baltimore, MD. MIM Number 188400; 10/13/00. Available at: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?188400.

TEXTBOOKS
Jones KL. Smith’s Recognizable Patterns of Human Malformation. 5th ed. Philadelphia, PA: W.B. Saunders Company; 1997:616-17.

Behrman RE, et al., eds. Nelson Textbook of Pediatrics. 15th ed. Philadelphia, PA: W.B. Saunders Company; 1996:571.

Buyse ML. Birth Defects Encyclopedia. Dover, MA: Blackwell Scientific Publications, Inc.; 1990:357-58, 393, 961-62.

Gorlin RJ, et al., eds. Syndromes of the Head and Neck. 3rd ed. New York, NY: Oxford University Press; 1990:84, 94-95, 663-666.

JOURNAL ARTICLES
Van Esch H, et al. The phenotypic spectrum of the 10p deletion syndrome versus the classical DiGeorge syndrome. Genet Couns. 1999;10:59-65.

Van Esch H, et al. Partial DiGeorge syndrome in two patients with a 10p rearrangement. Clin Genet. 1999;55:269-76.

Hsu HL, et al. Partial DiGeorge anomaly associated with 10p deletion. J Formos Med Assoc. 1997;96:996-99.

Dasouki M, et al. DiGeorge anomaly and chromosome 10p deletions: one or two loci? Am J Med Genet. 1997;73:72-75.

Schuffenhauer S, et al. DiGeorge syndrome and partial monosomy 10p: case report and review. Ann Genet. 1995;38:162-67.

Shapira M, et al. Deletion of the short arm of chromosome 10 (10p13)/Report of a patient and review. Am J Med Genet. 1994;52:34-38.

Kinoshita Y, et al. A case of deletion of the short arm of chromosome 10 with severe hearing loss and brainstem dysfunction. Am J Perinatol. 1992;9:299-301.

Obregon MG, et al. Partial deletion 10p syndrome. Report of two patients. Ann Genet. 1992;35:101-04.

Monaco G, et al. DiGeorge anomaly associated with 10p deletion. Am J Med Genet. 1991;39:215-16.

Koenig R, et al. Partial monosomy 10p syndrome. Ann Genet. 1985;28:173-76.

Elstner CL, et al. Further delineation of the 10p deletion syndrome. Pediatrics. 1984;73:670-75.

Fryns JP, et al. Distal 10p deletion syndrome. Ann Genet. 1981;24:189-90.

Klep-de Pater JM, et al. Partial monosomy 10p syndrome. Eur J Pediatr. 1981;137:243-46.