• partial trisomy 9p
• chromosome 9
• chromosome 5
• cri du chat syndrome

Partial trisomy or tetrasomy of the short arm of chromosome 9 are among the most common autosomal structural chromosomal anomalies in humans, so the phenotype-genotype correlation of these aneusomies has been well described. Characteristic clinical features of partial trisomy 9p are mental retardation of various degree, short stature, craniofacial abnormalities, short fingers, simian crease, and single crease of the fifth finger. Additional symptoms like microcephaly, cleft lip and palate, malformed ears, and skeletal, nail, cardiac, and genital anomalies have also been observed.^1,2 In 1970, the first case of trisomy 9p was reported by Réthoré et al.³ Since then, more than 150 patients with partial or complete trisomy 9p have been reported. In most patients, the trisomic segment was transmitted from a parent carrying a reciprocal balanced translocation and only a small number arose from de novo duplications.

Here we report on a three generation family with an interchromosomal insertion of chromosome 9p12-p21 material into the short arm of chromosome 5. One member of the family carried a deletion in the inserted region resulting in cri du chat syndrome, whereas her father is trisomic for the inserted segment owing to an unbalanced segregation of the insertion chromosome. Surprisingly, the unbalanced insertion carrier does not show any morphological or mental abnormalities. The normal phenotype suggests that not all partial trisomies 9p are associated with clinical abnormalities. In particular, the proximal part of the short arm of chromosome 9 seems to be less important for the trisomy 9p phenotype.