A newborn boy is evaluated in the hospital nursery 2 hours after birth. The patient was born at 39 weeks of gestation to a 30-year-old primigravid via vaginal delivery. The patient’s mother received routine prenatal care and the pregnancy was uncomplicated. The patient’s anatomy ultrasound at 20 weeks of gestation was unremarkable. The patient’s mother denies any family history of genetic diseases. The patient’s APGAR scores were notable for poor muscle tone at both 1 and 5 minutes of life. The patient’s birth weight is 2.6 kg (5 lb 11 oz), which is at the 5th percentile. His height and head circumference are in the 15th and 3rd percentile, respectively. His temperature is 97.1°F (36.2°C), blood pressure is 57/42 mmHg, pulse is 140/min, and respirations are 38/min. On physical exam, the patient has a wide nasal bridge, down slanting palpebral fissures, and widely spaced eyes. He has good respiratory effort with a high-pitched cry. This patient is most likely to have experienced a deletion on which of the following chromosomes?
4p
5p
7q
15q
5p
This patient presents with a characteristic mew, microcephaly, hypertelorism, wide nasal bridge, and hypotonia, which suggests a diagnosis of cri-du-chat syndrome. Cri-du-chat syndrome is caused by a deletion on chromosome 5p.

Cri-du-chat syndrome is most commonly caused by a de novo partial deletion of chromosome 5p. Other cases may be caused by a parental translocation involving the relevant section of chromosome 5p. Patients present with a mew-like cry, microcephaly, hypertelorism, down slanting palpebral fissures, a broad nasal bridge, low-set ears, low birth weight, hypotonia, and intellectual disability. The cat-like cry usually resolves by 2 years of age. Treatment is supportive though some patients may have cardiac abnormalities that require surgical intervention.

Cerruti Mainardi reviews the evidence regarding the etiology and diagnosis of patients with Cri-du-chat syndrome. She discusses how the diagnosis is mostly made clinically at this time. She recommends karyotype and FISH studies for those with ambiguous features.

Incorrect Answers:
Answer A: A deletion on chromosome 4p causes Wolf-Hirshhorn syndrome, which presents with growth restriction, microcephaly, congenital heart disease, severe intellectual disability and dysmorphic "Greek warrior helmet" facies of a high forehead, prominent glabella, arched eyebrows, hypertelorism, and epicanthal folds. Treatment is supportive though some patients may require surgical intervention for heart defects.

Answer C: A deletion on chromosome 5q results in Sotos syndrome, a pediatric overgrowth disorder characterized by an increase in head circumference, hypotonia, delayed acquisition of motor skills, and mild intellectual disability.

Answer D: A deletion on chromosome 7q may results in Williams syndrome, which presents with dysmorphic, “elfin” facies, global developmental delay with a hypersocial personality, and supravalvular aortic stenosis. Treatment is supportive though some patients will require surgical intervention for aortic stenosis.

Answer E: A deletion on chromosome 15q may cause either Prader-Willi syndrome or Angelman syndrome, depending on whether the deletion affects the maternal or paternal chromosome. Prader-Willi syndrome classically presents with dysmorphic facies, hyperphagia, and hypogonadism. Angelman syndrome classically presents with intellectual disability, frequent smiling or laughing, and gait ataxia. Treatment is supportive with seizure control for those who develop seizures.

Bullet Summary:
Cri-du-chat syndrome (presents with a characteristic mew, microcephaly, hypertelorism, wide nasal bridge, and hypotonia) is most commonly caused by a deletion on chromosome 5p.