Most infants with Chromosome 9, Partial Monosomy 9p have a normal birth weight and length. However, the disorder is typically characterized by variable delays in the acquisition of skills requiring the coordination of mental and physical activities (psychomotor retardation) and moderate or mild mental retardation. Reports indicate that affected individuals tend to have an affectionate, friendly, and sociable personality.
As noted above, Chromosome 9, Partial Monosomy 9p is also associated with characteristic abnormalities of the skull and facial (craniofacial) region. In many affected infants, there is premature fusion of the fibrous joint (i.e., metopic suture) between bones forming the forehead (craniosynostosis), resulting in an abnormally narrow, pointed, “triangular-” or “keel-shaped” forehead (trigonocephaly). In addition, the back of the head (occiput) may appear unusually flat. Additional characteristic craniofacial malformations may include widely spaced eyes (ocular hypertelorism); upwardly slanting eyelid folds (palpebral fissures); vertical skin folds that may cover the eyes’ inner corners (epicanthal folds); and/or highly arched eyebrows. In addition, the eyes may appear unusually prominent. Many affected infants also have unusually flat midfacial regions (midfacial hypoplasia), including a short nose, flattened nasal bridge, and upturned nostrils (anteverted nares); an abnormally long vertical groove in the center of the upper lip (philtrum); and/or a small jaw (micrognathia) and small mouth with protruding lips. Additional Craniofacial abnormalities may also be present, such as a highly arched roof of the mouth (palate); low-set, malformed ears; and/or a short, broad, somewhat webbed neck with a low hairline.
Individuals with Chromosome 9, Partial Monosomy 9p may also have various malformations of the hands and feet. Such abnormalities may include unusually long fingers or toes (digits) due to increased length of the middle bones (phalanges) of the digits; abnormal skin ridge patterns of the fingertips; a single crease across the palms of the hands; and/or abnormally short, square (i.e., hyperconvex) fingernails and toenails.
According to reports in the medical literature, approximately one- to two-thirds of affected infants may also have structural malformations of the heart at birth (congenital heart 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 defects); abnormal narrowing (stenosis) of the opening between the pulmonary artery and the right ventricle (pulmonary stenosis); and/or patent ductus arteriosus (PDA). In individuals with PDA, the channel that is present between the pulmonary artery and the aorta during fetal development fails to close after birth. (The pulmonary artery carries oxygen-depleted blood from the right ventricle to the lungs, where the exchange of oxygen and carbon dioxide occurs. The aorta, the major artery of the body, arises from the left ventricle and supplies oxygen-rich blood to most arteries.) In those with cardiac defects, associated symptoms and findings may vary, depending upon the size, nature, and combination of heart malformations present and other factors. Some individuals may show no apparent symptoms (asymptomatic), while others may develop Difficulties feeding, shortness of breath, profuse sweating, irritability, easy fatigability, bluish discoloration of the skin and mucous membranes (cyanosis), and/or other abnormalities. In severe cases, congenital heart disease may lead to potentially life-threatening complications.
In some individuals with the disorder, Chromosome 9, Partial Monosomy 9p may also be characterized by genital defects. In affected males, such abnormalities may include a small penis (micropenis); undescended testes (cryptorchidism); and/or abnormal placement of the urinary opening (hypospadias), such as on the underside of the penis. In females, the two long folds of skin on either side of the vaginal opening (labia majora) may be underdeveloped (hypoplastic), while the two small folds of skin between the labia majora and the vaginal opening (labia minora) may be larger than normal (hyperplastic).
In addition, in some affected infants, there may be protrusion (herniation) of a portion of the intestine into the canal that passes through lower muscular layers of the abdominal wall (inguinal hernia). (In males, the inguinal canal is the tubular passageway through which the testes normally descend from the abdomen into the scrotum before birth.) Some with the disorder may also have an umbilical hernia or an omphalocele. An umbilical hernia is a skin-covered protrusion of intestine and the fold of fatty membrane in front of the intestine (omentum) through a defect in the abdominal wall at the navel (i.e., the umbilicus, where the umbilical cord joined the fetal abdomen). An omphalocele is a herniation of varying amounts of abdominal contents (e.g., intestines and, in severe cases, other abdominal organs) around the umbilicus, with the bulging area covered by a membrane-like sac consisting of peritoneum without overlying skin. (The peritoneum is the membrane lining the abdominal wall and covering internal abdominal organs.) In infants with an omphalocele, potentially life-threatening complications may result due to rupture of the sac, damage to tissues due to drying, and/or infection.
Additional physical abnormalities have also been reported in association with Partial Monosomy 9p. Such abnormalities have included sudden episodes of uncontrolled electrical activity in the brain (seizures), widely spaced nipples, abnormal curvature of the spine, and/or, more rarely, incomplete closure (clefting) of the palate (cleft palate), bony or membranous blockage of the passageway between one or both sides of the nose and the throat (choanal atresia), and/or other features.