NB- In hypotelorism the interorbital distance is reduced. Hypotelorism per se is very rarte.
· Holoprosencephaly- The most common cause of hypotelorism is holoprosencephaly, although both these conditions are comparatively rare. Anomalies of the orbits, nose, median upper lip and palate occur.
· Trisomy 21- Associated features include increased nuchal fold, duodenal atresia, omphalocele, cystic hygroma, CHD, hypoplasia of the middle phalanx of the 5th finger, increased space between the 1st and 2nd toes and hydrops fetalis.
· Williams' syndrome- Inherited as autosomal dominant with variable expressivity, the features associated include CHD and several cardiovascular anomalies, micrognathia, hypotelorism, 5th finger clindactyly, camptodactyly, talipes equinovarus, kyphoscoliosis and pulmonary sequestration.
· Phenylketonuria- Hypotelorism in the fetus may be related to fetal effects of maternal phenylketonuria.
· Trisomy 13- Holoprosencephaly may occur as a part of trisomy 13. The most important sonographic findings of this condition are in the face, head, heart and hands. The facial anomalies include a cleft lip/palate and low set ears.
· Meckel's syndrome- This autosomal recessive condition is associated with occipital encephalocele, hydrocephalus, short limbs, CHD and dysplastic kidneys.
· DiGeorge's syndrome- Autosomal dominant; associated with hypoplastic mandible, low set ears, hyper/hypotelorism, cleft lip/palate, CHD, TOF, imperforate anus, hypocalcemic tetany and infections in the newborn.
· Fetal hydantoin syndrome- This syndrome is related to maternal ingestion of the anticonvulsant drug, hydantoin. Associated features include microcephaly, low set ears, cleft lip/palate, limb anomalies, CHD, diaphragmatic hernia and cystic hygroma.
· Craniosynostosis- Associated features include dysplastic ears, hypotelorism/hypertelorism, cleft lip/palate, facial capillary hemangioma, craniosynostosis, radical aplasia, fibular aplasia, hand/foot and vertebrai anomalies.
· Microcephaly- Microcephaly is associated with many syndromes and environmental factors resulting in insult to the developing brain, e.g. infection, drugs. Diagnosis may be difficult as microcephaly may not develop until late in pregnancy. Poor head growth leads to a decline in the head:abdomen ratios.
· Oculodental dysplasia- Inherited in an autosomal dominant manner with variable expressivity, associated features include syndactyly, camptodactyly, clindactyly, phalanx aplasia., dysplasia or hypoplasia, cleft lip/palate, microphthalmos, hypotelorism and a thin nose.
· Trigonocephaly- The condition is inherited as autosomal dominant; associated features include trigonocephaly, due to premature fusion of metopic
sutures, hypotelorism, omphalocele, hemivertebrae and minor malformations of fingers and toes.
· Chromsome 18p syndrome- This syndrome is caused by deletion of the short arm of chromosome 18. Most features of this condition may be difficult to detect antenatally. The features include craniofacial dysmorphism, hypo/ hypertelorism, small chin, big protruding ears, kyphoscoliosis and curved 5th finger. The characteristics are obvious after birth.
· Chromosome 5p syndrome- Associated features include IUGR, micrognathia, microcephaly, hypertelorism, low set ears, CHD, scoliosis and small iliac wings.
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