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Solitary median maxillary central incisor (SMMCI) syndrome
Roger K Hall

Correspondence: Roger K Hall [email protected]

Author Affiliations
Department of Dentistry, Royal Children's Hospital, Flemington Rd Parkville, 3052 Victoria, Australia
Orphanet Journal of Rare Diseases 2006, 1:12 doi:10.1186/1750-1172-1-12

The electronic version of this article is the complete one and can be found online at:

Received: 21 March 2006
Accepted: 9 April 2006
Published: 9 April 2006

© 2006 Hall; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Solitary median maxillary central incisor syndrome (SMMCI) is a complex disorder consisting of multiple, mainly midline defects of development resulting from unknown factor(s) operating in utero about the 35th–38th day(s) from conception. It is estimated to occur in 1:50,000 live births. Aetiology is uncertain. Missense mutation in the SHH gene (I111F) at 7q36 may be associated with SMMCI. The SMMCI tooth differs from the normal central incisor, in that the crown form is symmetric; it develops and erupts precisely in the midline of the maxillary dental arch in both primary and permanent dentitions. Congenital nasal malformation (choanal atresia, midnasal stenosis or congenital pyriform aperture stenosis) is positively associated with SMMCI. The presence of an SMMCI tooth can predict associated anomalies and in particular the serious anomaly holoprosencephaly. Common congenital anomalies associated with SMMCI are: severe to mild intellectual disability, congenital heart disease, cleft lip and/or palate and less frequently, microcephaly, hypopituitarism, hypotelorism, convergent strabismus, oesophageal and duodenal atresia, cervical hemivertebrae, cervical dermoid, hypothyroidism, scoliosis, absent kidney, micropenis and ambiguous genitalia. Short stature is present in half the children. Diagnosis should be made by eight months of age, but can be made at birth and even prenatally at 18–22 weeks from the routine mid-trimester ultrasound scan. Management depends upon the individual anomalies present. Choanal stenosis requires emergency surgical treatment. Short stature may require growth hormone therapy. SMMCI tooth itself is mainly an aesthetic problem, which is ideally managed by combined orthodontic, prosthodontic and oral surgical treatment; alternatively, it can be left untreated.

Disease name and synonyms
The name originally given to this syndrome by Hall et al. [1], "Solitary median maxillary central incisor, short stature, choanal atresia/midnasal stenosis syndrome", is now customarily shortened to the first part of this name: "Solitary median maxillary central incisor syndrome" or SMMCI syndrome, as the other features are not necessarily present in all cases. The use of the full description of the single incisor tooth in the name is important, as it emphasises the unique form and position of this tooth, which is the characteristic and most readily observed feature or trait of the condition.

The early observations of this condition [2-8] merely referred to the congenital and hereditary absence of one central incisor. When the association with short stature was recognised in 1976, the name Monosuperoincisivodontic dwarfism was given by Rappaport et al. [9], but it was soon recognised that short stature was not always present in the disorder [10]. The names "single central incisor syndrome" or "single maxillary central incisor" or "single incisor" suggested by other authors [11-15], do not adequately describe the peculiarly formed incisor tooth.

To accurately describe the characteristic tooth present in this syndrome, it is necessary to specify:

• Solitary: the tooth present exists as the only central incisor tooth in...

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