Beginning of the story

A smiling boy showing symptoms of macrocephaly at birth

A boy was born to a family with a cute 2-year-old sister. He was born at 38 weeks of gestation to unrelated parents.
His delivery was done with a Caesarean section due to the mother’s polyhydramnios(too much amniotic fluid around the baby) and the baby’s abnormal heart rate.
He weighed 3.9kg with a head circumference of 37cm(>97th percentile), which is relatively large.

Features presented after birth

Three features observed at birth from the boy with Molybdenum cofactor deficiency type B

When born, the boy was not in good condition. He was breathing irregularly, had pale grey skin, and had increased muscle tone(rigid and hard to move).
Due to the low saturated oxygen and mild acidity of umbilical cord blood, Mechanical ventilation had to be performed.

There was no family history associated with pregnancy.

Physical examinations

Five features observed from the boy with Molybdenum cofactor deficiency type B after physical examinations

Physical examinations have found facial dysmorphism(coarse features with puffy cheeks, bitemporal narrowing, deep-set eyes, long philtrum, dysplastic auricles), long and overlapping fingers, large feet, pectus excavatum, swelling of the eyelids.

Results of extra tests

A brain MRI result showing cerebellar hypoplasia and dilated cerebellar fluid spaces

Extra tests, such as cardiac ultrasonography, Brain MRI, blood test, and urine test, were conducted to look into his conditions.

The tests revealed hypertrophic cardiomyopathy(abnormally thick heart muscle), cerebellar hypoplasia(small or underdeveloped cerebellum), and dilated cerebellar fluid spaces. Unusually low serum uric acid and serum homocysteine in the blood and positive sulfite dipstick results were also observed.

Condition of the boy getting worse

On the day of birth, convulsion and stiff limbs were observed. Over the next few days, the patient became more inactive, flaccid(too soft and weak), and showed abnormal movements of extremities. Nonrhythmic waving, pedaling, and increased muscle tone were observed mainly in the upper extremities.

Medication(Levetiracetam) to treat seizures had an initial effect, but contracture in elbow and knee joints gradually have appeared.
In the second month after birth, the boy showed axial hypotonia(low muscle tone of the trunk), lower limb spasticity(contracted muscle), tendon hyperreflexia, and epileptic seizures.

Nonspecific features make diagnosis difficult

Due to the blood test result, his distinctive facial feature, and neurological problem, the doctor suspected Molybdenum cofactor deficiency. However, since the boy was also presenting nonspecific features like macrocephaly at birth, hypertrophic cardiomyopathy(restrictive), and lack of cystic leukomalacia, whole exome sequencing was conducted with 3billion.

The boy’s life after WES

A molecule written MOCS2

The WES result found a novel variant on the MOCS2 gene. Even though the variant was classified into a variant of unknown significance(VUS), The doctor gave diagnosis due to the consistency between his clinical features and the disease’s known features, and other supporting facts.

The boy's final diagnosis was 'Molybdenum cofactor deficiency type B(MOCODB).' To learn details about the disease, visit Rare Disease Series #15: MOCODB.

Although he was diagnosed, the boy was shifted to a home hospice due to his serious and worsening clinical conditions.


  1. ic_Disease-1
  2. Disease:
    Molybdenum cofactor deficiency type B (MIM# 252160)
    Gene: MOCS2
    Please refer to the Rare Disease Series #15: Molybdenum cofactor deficiency type B(MOCODB)
Stay tuned for 3billion’s next 'My Odyssey' series. We will deliver more diagnostic stories of patients diagnosed with us. Thank you.

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