Williams-Beuren. This is a contiguous gene syn­drome, which, in full-blown form, includes supravalvular aortic stenosis (SVAS), multiple peripheral pulmonary arterial stenoses, elfin face, psychomotor and developmen­tal delay, characteristic dental malformations, and infan­tile hypercalcemia in some cases. Ninety-six percent of patients with Williams syndrome have a micro-deletion of chromosome 7 (critical region 7q11.23) when examined with FISH analysis (Fig. 1) which is a rapid and informa­tive test to confirm a clinical diagnosis of the syndrome. This micro-deletion has a misfunction of many genes, one of which is the elastin gene which is responsible for the phenotype of Williams syndrome. However, the presence of two copies of the elastin locus in a patient does not rule out the diagnosis [11-13].

Di George (CATCH 22). Di George syndrome com­prises mental retardation, short stature, characteristic fa­cies, abnormalities of the aortic arch, hypoplasia of thymus and of parathyroid glands resulting in hypocalcemia, and finally, seizures. Most cases result from a micro-deletion of chromosome 22q1.2 (Fig. 2). Several genes are lost including the putative transcription factor TUPLE 1 which is expressed in the appropriate distribution. This deletion may present with a variety of phenotypes: Di George syn­drome, Sphrintzen syndrome, conotruncal anomaly face (or Takao syndrome), and isolated outflow tract defects of the heart including tetralogy of Fallot, truncus arteriosus, and interrupted aortic arch. A collective acronym CATCH 22 has been proposed for these differing presentations. A small number of cases of Di George syndrome have de­fects in other chromosomes, notably 10p13 [11,14-16,18].

Velocardiofacial or Sphrintzen (CATCH 22). Velo­cardiofacial syndrome is associated with a broad clinical spectrum that frequently overlaps with the Di George syn­drome. Both have been linked to chromosomal micro-deletions of chromosome 22 (22q11.2). The main features of this syndrome are: mental retardation, nasal speech, characteristic facies, various congenital heart abnormali­ties and increased incidence of immunological disturb­ances, mostly cytopenias [15-18].

Angelman (happy puppet). This syndrome is mainly characterized by psychomotor retardation, ataxia, hypo­tonia, odd facies and seizures. It is caused from a micro-deletion of chromosome 15 (critical region 15q11.2-q12) (Fig. 3) of maternal origin. Other mechanisms responsible for the Angelman syndrome are paternal disomy (imprint­ing) of chromosome 15 or point mutations in the above mentioned critical region of chromosome 15 [18,19,22].

Prader-Willi. The main features of this syndrome are: characteristic facial, mental retardation, diminished fetal activity, failure to thrive initially, obesity in later life, muscular hypotonia, short stature, hypogonadotrophic hypogonadism, and small hands and feet. It can be caused by deletion or disruption of a gene, or several genes, on the proximal long arm of paternal chromosome 15 (critical region 15q11.2-q12) (Fig. 3) or maternal uniparental di­somy 15, because the gene(s) on the maternal chromo­some(s)15 are virtually inactive through imprinting [18-22].

Pitt-Rogers-Danks. The main features of this syn­drome are: intrauterine growth retardation, short stature, characteristic facies and microcephaly. A micro-deletion of chromosome 4 (critical region 4p16.3) is responsible for this syndrome [23,24].