Genetic counseling: Craniosynostosis-1

Craniosynostosis

Overview

 * Craniosynostosis refers to the premature fusion of the cranial sutures (growth centers between the bones of the skull)
 * The skull is made up of a number of bones and when those bones fuse together too soon it doesn't allow the head to grow in the usual fashion and can lead to changes in head shape
 * Usually cranial sutures do not fuse completely until the fourth decade

Primary vs. secondary craniosynostosis

 * Primary
 * suture growth is altered
 * head frequently assymmetric
 * the brain continues to grow in areas where sutures are open
 * most individuals are normal neurologically
 * benefit from surgery
 * Secondary
 * growth of brain is impaired
 * neurologically abnormal usually

Isolated vs. Syndromic

 * Isolated
 * usually presents during first year of life
 * usually involves only one cranial suture (may involve more than one though)
 * no other associated abnormalities except those produced secondarily as a result of premature fusion of suture
 * sagittal suture is most common site for isolated craniosynostosis
 * suture that runs from front to back and separates parietal bones
 * results in head elongated from front to back due to limited growth laterally (scaphocephaly)
 * intracranial pressure is usually in the normal range
 * cranial surgery usually recommended to give a more usual head shape
 * usually babies with isolated craniosynostosis grow and develop normally
 * Syndromic
 * Other characteristic features present
 * over 60 syndromes described with craniosynostosis as a feature
 * bicoronal synostosis is the type present in the most common syndromes
 * Most follow AD inheritance
 * Most individuals with a craniosynostosis syndrome have normal intelligence
 * Saethre-Chotzen syndrome is the most common
 * characterized by facial asymmetry, low frontal hairline, ptosis, deviated nasal septum, brachydactyly, and partial cutaneous syndactyly of the toes
 * Crouzon - next most common (1 in 25,000 live births)
 * characterized by maxillary hypoplasia, shallow orbits, and ocular proptosis
 * Apert syndrome
 * characterized by strabismus, maxillary hypoplasia
 * complete symmetrical syndactyly of hands and feet
 * associated with risk for developmental delay (unlike most of the other AD craniosynostosis syndromes)
 * Pfeiffer syndrome
 * maxillary hypoplasia
 * broad thumbs and big toes
 * mild cutaneous syndactyly

Incidence of isolated nonsyndromic craniosynostosis

 * 0.4-0.6 per 1000 births
 * so about 1 in 2000 births (Fetology, 2000)

Recurrence risks for isolated nonsyndromic craniosynostosis

 * usually sporadic
 * genetic basis not discovered except for certain cases of unicoronal synostosis
 * In study of 125 patients with craniosynostosis only 2.5% of those with isolated synostosis had positive family history
 * patients with isolated craniosynostosis and a negative family history are not believed to have an increased incidence of recurrence above the background

Ultrasound detection of craniosynostosis
Surgery
 * difficult to detect on ultrasound
 * when it is detected it is often not until 3rd trimester
 * sometimes features associated with syndrome are detected on ultrasound (fused digits etc)
 * objective is to allow adequate brain growth and imporve appearance
 * Surgery for isolated craniosynostosis is usually a single operation and produces excellent cosmetic results in 93%