Am Fam Physician. 2000;62(5):958-960
The article “Identification and Evaluation of Mental Retardation” (February 15, page 1059) contained an error in Table 2; the correct term for the fourth entry in the diagnosis column should be velocardiofacial syndrome rather than DiGeorge syndrome. The corrected table is reprinted on the following pages.
| Diagnosis | Incidence | Etiology, including inheritance | Clinical manifestations and early recognition | Associated conditions | Diagnostic evaluation* | Prognosis | Special considerations |
|---|---|---|---|---|---|---|---|
| Down syndrome | 1 in 600 to 800 births | Results from extra copy of chromosome 21, usually a sporadic event; 2% of cases may be inherited from a balanced translocation carrier parent | Hypotonia; flat facial profile; upslanting palpebral fissures; small ears; in-curving fifth fingers; single transverse palmar creases | Slow growth; congenital heart defect; thyroid dysfunction; developmental delay, especially speech | Chromosome analysis in all patients; chromosome analysis of parents if translocation is found; pediatric cardiology evaluation with echocardiogram by 6 weeks of age | Cognitive limitations, with most in mild to moderate MR range; decreased life expectancy can be associated with congenital heart defect, especially if not recognized in early infancy | Except in cases where parent has a translocation, risk for recurrence is 1% |
| Fetal alcohol syndrome | 0.05 to 3 in 1,000 children diagnosed annually in United States | Alcohol consumption by mother during pregnancy | Diagnosis can be made at birth, based on history, baby's facial features (medial epicanthal folds, wide nasal bridge, small upturned nose, long philtrum, narrow or wide upper lip), low birth measurements | May include retardation, behavior problems, ADHD, seizures, autism | Good history and physical examination imperative; history of maternal drinking, pre- and postnatal growth retardation, dysmorphic facial features, CNS involvement; no laboratory tests available | Varies; growth may improve during adolescence and facial features may soften, but behaviors may cause serious problems | Many of these children are adopted; FAS and fetal alcohol effects (usually developmental and behavioral problems) are totally preventable |
| Fragile X syndrome | 1 in 2,000 to 3,000 male live births; females may also be affected | Abnormality in FMR-1 gene located on X chromosome; inherited in X-linked manner so males are more severely affected | Macrocephaly; large ears; enlarged testicles after puberty; hyperextensible fingers | Autism/autistic- like behaviors; developmental delay, especially speech; clumsiness; mitral valve prolapse | DNA testing for fragile X mutation (chromosome testing for fragile X misses up to 7% of cases); mothers of affected boys are obligate carriers of the gene | Normal life expectancy; mild to profound MR | Females usually less severely affected than males; up to 50% of females with mutation have MR or educational difficulties; risk for recurrence is 50% |
| Velocardio- facial syndrome | 1 in 700 live births | Deletion of chromosome 22; usually de novo but may be inherited in an autosomal dominant manner | Cleft palate; congenital heart defect; speech delay; elongated face with almond- shaped eyes; wide nose with hypoplastic alae nasi; small ears; slender, hyperextensible fingers | Learning disabilities ± mild MR; psychiatric disorder in 10% | High-resolution chromosome analysis with chromosome painting (FISH) to detect chromosome 22 deletion; parents should also be tested | Normal life expectancy unless severe heart defect (e.g., truncus arteriosus, interrupted aortic arch) is present | Risk for recurrence as high as 50%, depending on family history |
| Unknown cause of MR | 30 to 50% of all cases of MR | Variable; diagnosis may evolve over time, so repeated evaluations may be helpful | Nonspecific cluster of minor malformations; delayed milestones, especially language development | Behavioral phenotype may also aid diagnosis as course evolves | Cytogenetic studies; brain imaging; metabolic studies | Will vary considerably based on etiology (if it can be established) and/or severity | Diagnostic techniques that may aid in diagnosis are constantly being refined |