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Solitary median maxillary central incisor syndrome
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 from about the 35th-38th day after conception.
It is estimated to occur in 1:50,000 live births.
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 SMMCI tooth may be predictive of associated anomalies, and 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.
The aetiology is uncertain. A missense mutation in the SHH gene (I111F) at 7q36 may be associated with SMMCI.
Diagnosis should be made by 8 months of age, but can be made at birth and even prenatally at 18-22 weeks from the routine mid-trimester ultrasound scan.
Management and treatment
Management depends upon the individual anomalies present. Choanal stenosis requires emergency surgical treatment and 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.