A deletion in the short arm of chromosome 5 is responsible forcri du chat syndrome, with its characteristic catlike cry duringearly infancy, the result of tracheal hypoplasia. Other clinical features include low birth weight and postnatal failure to thrive, hypotonia, developmental disability, microcephaly, andcraniofacial dysmorphism, including ocular hypertelorism,epicanthal folds, downward obliquity of the palpebral fissures,and low-set malformed ears. Clefts of the lip and palate, congenital heart disease, and other malformations may be seen.
The clinical severity of cri du chat syndrome depends on thesize of the chromosomal deletion. Larger deletions are associated with more severe expression. Most cases arise de novo;the deletion is usually in the chromosome 5 inherited from thefather.
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Williams syndrome is due to a small deletion of chromosome 7q11.2. Congenital heart disease is seen in 80% of affected children, with supravalvar aortic-valve and pulmonic-valve stenosis and peripheral pulmonic stenosis being the most common anomalies. Although these children often have normal birth weight, they have growth delay, manifesting short stature. They have a distinctive facial appearance (“elfin facies”), with median flare of the eyebrows, fullness of the perioral and periorbital region, blue irides with a stellate pattern of pigment, and depressed nasal bridge with anteversion of the nares. Moderate intellectual disability (average IQ in the 50 to 60 range) is common, but developmental testing reveals strength in personal social skills and deficiencies in cognitive areas. Hypercalcemia is present in neonates.
Individuals with Williams syndrome often have a striking personality. Loquacious and gregarious, they are frequently described as having a cocktail party personality. However, approximately 10% of children with Williams syndrome have features of autism spectrum disorder. Patients occasionally have unusual musical ability (about 20% have absolute or perfect pitch). Most children with Williams syndrome have a de novo deletion. In rare cases, the deletion is inherited from a parent in an autosomal dominant pattern.
WAGR syndrome (Wilms tumor, aniridia, genitourinary anomalies, and mental retardation) is caused by a deletion of 11p13 and is generally a de novo deletion. Genitourinary abnormalities include cryptorchidism and hypospadias. Patients often have short stature, and half may have microcephaly. Wilms tumor develops in 50% of patients with aniridia, genitourinary abnormalities, and mental retardation (see Chapter 159).
SEE CHAPTER 47.
SEE CHAPTER 47.
Chromosome 22q11.2 Deletion Syndromes
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Deletions of chromosome 22q11.2 are responsible for a group of findings that have been called by several names, including velocardiofacial syndrome, conotruncal anomaly face syndrome, Shprintzen syndrome, and DiGeorge syndrome.
These conditions represent a continuum of findings, virtually all of which are due to the chromosomal deletion.