|chromosome 9||medical dictionary|
Trisomy 9 can be homogenous or mosaic. Microcephaly with dolichocephaly, enophthalmy and microretrognathia are present. Characteristic osteoarticular anomalies include dislocation of the hips, knees or elbows, deformities of the spinal cord and rib anomalies. Inner organ malformations involve cardiac, cerebral, renal and occasionally digestive anomalies. The prognosis is most severe.
The 9p monosomy syndrome is characterised by trigonocephaly, long upper lip with undefined philtral borders, short nose, anteverted nares, psychomotor retardation, upward slant of palpebral fissures, dolichomesophalangy. Malformations are severe. The majority of the cases occur de novo, or can result from a parental translocation. 9p trisomy was the first partial trisomy identified before the use of banding techniques and is probably one of the most frequently detected. The majority of pure 9p trisomies occur de novo. In 9q trisomy and associated 9p trisomy, malsegregation of a parental rearrangement is always involved. Craniofacial dysmorphism includes brachycephaly, bulbous nose and short upper lip with a very characteristic asymmetric grin when the mouth opens. The knit brows, slanted palpebral fissures and mouth give a particularly distinctive worried look. The palms are long in comparison with the fingers. A single palmar crease is constant. Malformations are rare in cases of pure 9p trisomy but they are numerous and diverse in cases of associated 9p trisomy. Mental retardation is variable. Life expectancy is not impaired.
Tetrasomy 9p is remarkable due to the infrequency of autosomal tetrasomies. The phenotype is variable and the facial dysmorphism can resemble that of 9p trisomy. Malformations are severe and numerous. Homogeneous tetrasomies lead to early death. Mosaicism appears to diminish the severity of the outlook.
9q32 trisomy shows dolichocephaly, deep set eyes with short palpebral fissures, large poorly folded ears, beaked nose, marked microretrognathia, long abnormally implanted fingers and toes and severe developmental delay. Inner organ malformations involve the heart. The trisomy results from a tandem duplication arising de novo or from malsegregation of a parental rearrangement. Interstitial deletion 9q22-q32 is reported with multiple congenital anomalies.
Some major genes on chromosome 9 are those for the ABO blood group, fibroblast and leukocyte interferons, familial dysautonomia, Friedreich ataxia, nail-patella syndrome and galactose-1-phosphate uridyltransferase, whose deficiency causes galactosaemia.
(05 Mar 2000)
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