An 18-hour-old boy is evaluated in the emergency department for low muscle tone since birth. He was delivered at home to a 19-year-old woman at approximately 40 weeks gestation who received no prenatal care. Since birth, the infant has breastfed 4 times, has a weak suck each time, and falls asleep a few minutes after he begins nursing. Weight is 2.3 kg (5.1 lb). The eyes have upslanting palpebral fissures, and the mouth is open with a protruding tongue. The palate is narrow but intact. Cardiopulmonary examination is normal. The abdomen is soft with no hepatosplenomegaly. When the infant is held under the arms, his legs are extended and he almost slips through the examiner's hands. Which of the following is the most likely underlying diagnosis for this patient?

Question

An 18-hour-old boy is evaluated in the emergency department for low muscle tone since birth.  He was delivered at home to a 19-year-old woman at approximately 40 weeks gestation who received no prenatal care.  Since birth, the infant has breastfed 4 times, has a weak suck each time, and falls asleep a few minutes after he begins nursing.  Weight is 2.3 kg (5.1 lb).  The eyes have upslanting palpebral fissures, and the mouth is open with a protruding tongue.  The palate is narrow but intact.  Cardiopulmonary examination is normal.  The abdomen is soft with no hepatosplenomegaly.  When the infant is held under the arms, his legs are extended and he almost slips through the examiner's hands.  Which of the following is the most likely underlying diagnosis for this patient?

Quizplus · Accepted Answer

11ec25c8_d68e_eacf_bc81_8fa0b2fa0f6a_MD0003_00 Down syndrome is the most common condition caused by a chromosomal abnormality. Although prevalence correlates with increasing maternal age, children of young women can also be affected. Patients who are not identified on prenatal testing are typically recognized by physical examination at birth. Neonates with Down syndrome often have low birth weight (eg, <2.5 kg [5.5 lbs]) and dysmorphic features, including upslanting palpebral fissures, epicanthic folds, and a single palmar crease. single palmar crease Hypotonia is a prominent finding and can present with poor feeding due to a weak suck. On examination, an infant with weak muscle tone may have a protruding tongue. In contrast to infants with normal tone who have extremities flexed toward their bodies when held vertically, those with low tone may slip through the examiner's hands with arms and legs extended and floppy. Diagnosis is confirmed by an additional copy of chromosome 21 on karyotype. (Choice A) Beckwith-Wiedemann syndrome is a genetic condition characterized by macrosomia, hemihyperplasia (asymmetric overgrowth of one side of the body), omphalocele, and macroglossia. (Choice C) Fragile X syndrome is an X-linked disorder that may present with hypotonia in infancy but does not typically cause low birth weight. Fragile X syndrome (Choice D) Infant botulism classically presents with hypotonia and descending paralysis following ingestion of honey or dust contamined with Clostridium botulinum spores. This condition is unlikely in a 1-day-old and would not result in low birth weight or upslanting palpebral fissures. Signs of oculobulbar weakness (eg, ptosis) would be present. (Choice E) Prader-Willi syndrome (PWS) is due to loss of paternally inherited genes on chromosome 15 and can present in infancy with hypotonia. However, patients with PWS have hypogonadism and almond-shaped eyes rather than upslanting palpebral fissures. Educational objective: Hypotonia is a common finding in neonates with Down syndrome. Poor muscle tone and a weak suck are key findings. Additional features of Down syndrome in newborns include upslanting palpebral fissures, a protruding tongue, and a single palmar crease. References: Down syndrome related muscle hypotonia: association with COL6A3 functional SNP rs2270669. (http://www.ncbi.nlm.nih.gov/pubmed/23626599)

An 18-Hour-Old Boy Is Evaluated in the Emergency Department for Low