Mosaic trisomy 9 and lobar holoprosencephaly

Area of Science:

• Genetics
• Developmental Biology
• Pediatric Medicine

Background:

• Trisomy 9 syndrome is a chromosomal disorder with diverse clinical manifestations, including characteristic facial dysmorphisms and organ abnormalities.
• Mosaic trisomy 9 involves the presence of trisomic cells in some tissues but not all, leading to variable expressivity.
• Holoprosencephaly (HPE) is a spectrum of brain malformations resulting from incomplete cleavage of the embryonic forebrain.

Observation:

• A case of mosaic trisomy 9 syndrome is presented in a neonate with intrauterine growth retardation and multiple congenital anomalies.
• The patient exhibited facial features consistent with trisomy 9, including low-set ears, hypotelorism, and maxillary hypoplasia.
• Cytogenetic analysis confirmed mosaic trisomy 9 (17% trisomic cells), and pathology revealed lobar holoprosencephaly.

Findings:

• This case demonstrates a severe presentation of mosaic trisomy 9 syndrome associated with holoprosencephaly.
• The combination of trisomy 9 and HPE in this patient is rare, with only one prior report of arrhinia (a form of HPE) in mosaic trisomy 9.
• Facial anomalies observed in the propositus included hypotelorism, a single nostril, deeply set eyes, short palpebral fissures, and micrognathia.

Implications:

• This case raises important questions about the potential causative role of trisomy 9 in the etiology of holoprosencephaly.
• Further research is warranted to understand the genetic mechanisms linking trisomy 9 and HPE.
• The findings underscore the importance of comprehensive genetic and phenotypic evaluation in infants with complex congenital anomalies.