In 1973, Alfi et al. reported three infants with partial deletion of the short arm of chromosome 9 distal to band 9p22 who had several clinical features in common. In 1976, after identifying three additional patients with the same chromosomal deletion, this group described the deletion 9p syndrome.
The deletion 9p syndrome is very rare. It is estimated to occur in one in 50,000 newborns. Since its first description, well over 100 patients have been described in the literature, but there are likely many more people affected who have either not been diagnosed or not been reported. New cases have been published occasionally that describe new features associated with deletion 9p syndrome. Whether these new features are truly part of the syndrome or only accidentally occur together remains unclear.
This syndrome is defined by deletion of the short arm of the 9th chromosome. In most cases, the breakpoint is reported in the bands from 9p21 to 9p24. The majority of cases are de novo deletions, but parental translocations are also reported. The phenotype of deletion 9p is heterogeneous and no clear correlation between breakpoint and clinical features has been established. Common features of the syndrome include mental deficiency, psychomotor and speech delay, craniofacial dysmorphism, and other congenital malformations. The syndrome appears to be balanced between males and females.
Clinical features of deletion 9p syndrome:
Common features of this syndrome include trigonocephaly with prominent forehead, small upslanting palpebral fissures, flat nasal bridge, orbital hypertelorism, long philtrum, low set dysplastic ears and long phalanges with excess of whorls. In a case series of 11 patients, the mean IQ of the patients was 48. However, the intellectual disability can range from mild to severe. Additional malformations include choanal atresia, midface hypoplasia, high arched palate, small mouth, micrognathia, and short webbed neck. Obstructive sleep apnoea may complicate these midfacial malformations. Beyond the craniofacial anomalies, the most common congenital malformations are cardiac defects (ventricular septal defect, patent ductus arteriosus and pulmonary stenosis), inguinal and diaphragmatic hernias, pylorus stenosis, omphalocele, genital and/or gonadal dysgenesis, scoliosis and/or kyphosis, and pectus excavatum. EEG changes, seizure disorders, and developmental delay of speech and motor development with truncal hypotonia are also frequently reported.
Terminal deletions of the short arm of chromosome 9 have been associated with XY sex reversal, with or without additional features of the deletion 9p syndrome. The degree of the sex reversal is variable.
Recurrent ear, respiratory and urinary tract infections are reported frequently in this patient population. Recurrent aspirations can be attributed to muscular hypotonia with impaired swallowing and coughing, gastrooesophageal reflux, diaphragmatic hernias, and pylorus stenosis. Allergies and asthma are common, but specific immunological impairments are rarely identified.