In individuals with chromosome 10, distal trisomy 10q, an extremely rare chromosomal disorder, the end (distal) portion of the long arm (q) of one chromosome 10 (10q) is duplicated (trisomic). Symptoms and physical characteristics associated with the disorder may vary greatly in range and severity, depending upon the exact size and location of the duplicated portion of chromosome 10q. However, in most cases, the disorder is characterized by mild to severe mental retardation; distinctive malformations of the head and facial (craniofacial) area; also, there are sometimes defects of the hands and/or feet; and/or skeletal, heart (cardiac), kidney (renal), and/or respiratory (pulmonary) abnormalities. It is important to note that affected infants will not have all of the abnormalities listed below.
In most cases, chromosome 10, distal trisomy 10q is characterized by abnormally slow growth before and after birth (prenatal and postnatal growth retardation). In addition, most affected infants and children have mild to severely diminished muscle tone (hypotonia). Some may have abnormal looseness or laxity of the joints (generalized hyperlaxity). Infants and children with chromosome 10, distal trisomy 10q also have mild to severe intellectual disability and may experience profound delays in the acquisition of skills that require coordination of mental and muscular activities (psychomotor retardation).
In addition, infants and children with the disorder have characteristic malformations of the head and facial (craniofacial) area. Such abnormalities may include an abnormally small head (microcephaly) with a high, broad forehead; a round, slightly flattened face; prominent cheekbones; and/or low-set, misshapen ears that may appear rotated toward the back of the head (posteriorly rotated). Affected infants and children may also have a small nose with turned up nostrils (anteverted nares) and a broad, flat, and/or depressed nasal bridge; a small, bow-shaped mouth with a prominent upper lip; an unusually small lower jaw; and/or, in some cases, incomplete closure of the roof of the mouth (cleft palate). Additional features may include unusually fine, highly arched eyebrows; drooping of the upper eyelid(s) (ptosis); abnormal narrowing of the eyelid folds (palpebral fissures) between the upper and lower eyelids (blepharophimosis); and/or vertical skin folds that may cover the eyes’ inner corners (epicanthal folds). In some cases, according to the medical literature, the presence of epicanthal folds may cause the eyes to appear widely spaced (ocular hypertelorism). In addition, in some affected infants and children, the eyes may appear abnormally small (microphthalmia) due to reduced diameter of the cornea, the front, clear portion of the eye through which light passes.
In some cases, infants and children with chromosome 10, distal trisomy 10q also have characteristic malformations of the hands and/or feet. Such abnormalities may include permanent flexion (camptodactyly) and/or overlapping of certain fingers; an unusually large distance between the great toes (hallux) and the second toes; webbing (syndactyly) between the second and third toes; and/or abnormal positioning of the feet (i.e., rocker-bottom feet). Affected infants and children may also have abnormal skin ridge patterns including underdeveloped (hypoplastic) ridge patterns on the hands and feet and/or abnormal deep grooves in the soles of the feet (plantar furrows).
Many infants and children with the disorder may also have additional skeletal abnormalities. Affected individuals may have abnormally thin ribs, 11 rather than 12 rib pairs, an abnormally short neck, abnormal front-to-back and side-to side curvature of the spine (kyphoscoliosis), and/or abnormal depression of the sternum, the bone forming the center of the chest (“funnel chest” or pectus excavatum). Affected infants and children may also exhibit abnormally delayed, immature bone development (delayed bone age). In some cases, underdevelopment (hypoplasia) of the shin bone (tibia) and/or the thigh bone (femur).
Approximately half of infants with chromosome 10, distal trisomy 10q may have defects of the heart that are present at birth (congenital heart defects), respiratory abnormalities, and/or malformations of the kidneys. Symptoms associated with congenital heart defects may vary greatly depending upon the exact nature, size, and location of the anatomical defect present. In some cases, associated symptoms and physical findings may include breathlessness due to the heart’s inability to pump blood effectively (heart failure); easy fatigability; bluish discoloration of the skin and mucous membranes (cyanosis) due to insufficient oxygen supply to these tissues; and/or increased susceptibility to repeated infections of the lungs (pneumonia). Renal malformations associated with chromosome 10, distal trisomy 10q may include underdevelopment of the kidneys (hypoplasia); development of cysts (cystic kidneys); and/or abnormal swelling (distention) of and accumulation of urine in the kidneys (hydronephrosis) and the tubes (ureters) that bring urine to the bladder (hydroureter). In severe cases, cardiac, respiratory, and/or renal abnormalities may result in life-threatening complications during the first years of life.
In some cases, infants and children with chromosome 10, distal trisomy 10q may have additional abnormalities. In approximately half of affected males, one or both of the testes may fail to descend into the scrotum (cryptorchidism).
Chromosome 10, distal trisomy 10q is an extremely rare chromosomal disorder in which part of the end (distal) portion of the long arm (q) of one chromosome 10 is duplicated. Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Pairs of human chromosomes are numbered from 1 through 22, and an additional 23rd pair of sex chromosomes which include one X and one Y chromosome in males and two X chromosomes in females. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 11p13” refers to band 13 on the short arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
The duplication of the distal portion of chromosome 10q is responsible for the symptoms and physical features that characterize this disorder. The range and severity of symptoms depend upon the exact length and location of the duplicated portion of chromosome 10q. In individuals with the disorder, the duplicated portion of 10q may begin as high on the chromosome as in band 10q22, or as far down as in band 10q25 and usually extends toward the end or “terminal” portion of chromosome 10q (qter); According to the medical literature, researchers suspect that duplication of bands 10q25 and 10q26 is critical for the expression of the characteristic features associated with the disorder. Often heart and kidney defects are related to the duplication of band 10q24.
In over 90 percent of reported cases, chromosome 10, distal trisomy 10q is due to a chromosomal balanced translocation in one of the parents. A translocation is said to be “balanced” if pieces of two or more chromosomes break off and trade places, creating an altered but balanced set of chromosomes. Balanced translocations are usually harmless to the carrier. However, in some cases, carriers may have reproductive cells (i.e., eggs in females, sperm cells in males) with an “unbalanced” set of chromosomes. Therefore, carriers of a balanced translocation may have an increased risk of having offspring with an unbalanced translocation (i.e., an altered set of chromosomes resulting in extra and/or missing chromosomal material in certain chromosomal locations). Chromosomal testing may determine whether a parent has a balanced translocation. If a child has partial trisomy 10q due to a parental translocation, they may also have a partial monosomy of another chromosome.
In some cases, chromosome 10, distal trisomy 10q may be due to a spontaneous (de novo) genetic change (mutation) that occurs for unknown reasons (sporadic). In such cases, because the mutation is not related to parental chromosomal makeup, the chromosomal abnormality is not inherited from the parents.
Chromosome 10, distal trisomy 10q is an extremely rare but well-defined chromosomal disorder that appears to affect males and females at about the same rate. More than 35 cases have been reported in the medical literature since the disorder was originally described in 1974 (J.J. Yunis). Many of the symptoms and physical features associated with the disorder are apparent at birth (congenital).
In some cases, the diagnosis of Chromosome 10, Distal Trisomy 10q may be determined before birth (prenatally) by specialized tests such as ultrasound, amniocentesis, and/or chorionic villus sampling (CVS). Ultrasound studies may reveal characteristic findings that suggest a chromosomal disorder or other developmental abnormalities in the fetus. During amniocentesis, a sample of fluid that surrounds the developing fetus is removed and studied. During chorionic villus sampling, a tissue sample is removed from a portion of the placenta. Laboratory studies performed on this fluid or tissue sample may reveal the presence of Distal Trisomy 10q.
Chromosome 10, Distal Trisomy 10q may also be diagnosed and/or confirmed after birth (postnatally) based upon a thorough clinical evaluation, identification of characteristic physical findings, and chromosomal studies. Small trisomies may not be detected on standard chromosomal studies and may require chromosomal microarray analysis.
Certain specific abnormalities that may occur in association with Distal Trisomy 10q may be detected and/or confirmed by specialized imaging studies and/or additional tests. For example, specialized x-ray studies and/or other imaging techniques may be used to confirm and/or characterize certain skeletal abnormalities and/or renal malformations potentially associated with the disorder. Congenital heart defects potentially associated with Chromosome 10, Distal Trisomy 10q may be detected, confirmed, and/or characterized by a thorough clinical evaluation and specialized tests that allow physicians to evaluate the structure and function of the heart (e.g., x-ray studies, electrocardiogram [EKG] echocardiogram, cardiac catherization).
The treatment of Chromosome 10, Distal Trisomy 10q is directed toward the specific symptoms that are apparent in each individual. Treatment may require the coordinated efforts of a team of specialists. Pediatricians; surgeons; physicians who specialize in diagnosing and treating skeletal abnormalities (orthopedists), disorders or malformations of the heart (cardiologists), or kidney abnormalities (nephrologists); physical therapists; and/or other health care professionals may need to systematically and comprehensively plan an affected child’s treatment.
The treatment of Chromosome 10, Distal Trisomy 10q is symptomatic and supportive. In some cases, surgery may be performed to correct certain craniofacial, skeletal, cardiac, renal, and/or other malformations that may be associated with the disorder. In such cases, the surgical procedures performed will depend upon the location and severity of the anatomical abnormalities and their associated symptoms.
Physicians may recommend preventive measures for affected infants and children who may be prone to repeated respiratory infections. Physicians may also regularly monitor affected individuals for such infections to ensure early detection and appropriate, prompt treatment.
A team approach for infants and children with this disorder may be of benefit and may include special medical, educational, and social support services. Genetic counseling will be of benefit for affected individuals and their families. Other treatment for this disorder is symptomatic and supportive.
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