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Condition report · Musculoskeletal

Microcephalic Osteodysplastic Primordial Dwarfism Type II

Whole genome sequencing reads the PCNT gene for inherited changes that cause microcephalic osteodysplastic primordial dwarfism type II, a condition of very small body and head size from before birth.

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About this condition

A rare inherited condition causing very small body and head size from before birth, with skeletal differences and a risk of blood vessel problems in the brain. It is caused by changes in both copies of the PCNT gene.

Microcephalic osteodysplastic primordial dwarfism type II, or MOPD II, is a rare inherited condition in which body and head size are very small from before birth. Adult height is typically between about 50 and 100 centimetres, and head growth slows over time, but intellect is typically normal. Other features can include hip and spine problems, small teeth, a high-pitched voice and a characteristic facial appearance.

The condition is caused by changes in both copies of the PCNT gene. PCNT makes pericentrin, a protein in the centrosome, a structure that helps organise cell division and anchors other proteins to it. Reduced cell proliferation is thought to contribute to the very small body and brain size.

Many people develop blood vessel problems in the brain, including moyamoya, where the arteries at the base of the brain narrow, and aneurysms, which can burst. Some people also develop insulin resistance or diabetes, and kidney differences can occur. Regular brain blood vessel imaging from diagnosis can allow early treatment of these problems.

MOPD II is inherited in an autosomal recessive way. Parents of an affected child are usually carriers, so each further child has a 1 in 4 chance of being affected and a 1 in 2 chance of being a carrier with no signs. Genetic counselling, carrier testing of relatives and prenatal testing in later pregnancies are available.

The condition we analyse

Microcephalic Osteodysplastic Primordial Dwarfism Type II (MOPD II)

Autosomal recessive

Caused by loss-of-function changes in both copies of PCNT, which encodes pericentrin, a protein of the centrosome that organises cell division. Reduced cell proliferation is thought to contribute to very small body and brain size.

Signs and symptoms

Severe growth restriction before and after birth, with adult height of about 50 to 100 cm (20 to 40 inches), and marked microcephaly; intellect is typically normal. Small teeth, a high-pitched voice and hip problems can occur. Many people develop blood vessel disease in the brain, including moyamoya and aneurysms, and insulin resistance and diabetes can develop.

What a diagnosis changes

Regular brain blood vessel imaging from diagnosis allows early treatment of moyamoya or aneurysms. Screening for insulin resistance and diabetes, and orthopaedic and dental care, are also recommended; growth hormone should be avoided unless growth hormone deficiency is present. Both parents of an affected child are usually carriers, so each further child has a 1 in 4 chance of being affected; genetic counselling and carrier testing of relatives are available.

Genes analysed

Also known as

Majewski osteodysplastic primordial dwarfism type II; microcephalic osteodysplastic primordial dwarfism type 2; microcephalic osteodysplastic primordial dwarfism with tooth abnormalities; microcephalic osteodysplastic primordial dwarfism, type II; MOPD II; MOPD type II; MOPD2; osteodysplastic primordial dwarfism type 2

MONDO:0008872OMIM 210720Orphanet 2637MedGen 96587Sources: [1][2][3]

Why whole genome sequencing

MOPD II is inherited in a recessive way, so carrier relatives can have no signs at all. Whole genome sequencing reads the PCNT gene in the same test.

Relatives can be offered carrier testing

Each further child of two carriers has a 1 in 4 chance of being affected and a 1 in 2 chance of being a symptom-free carrier. Once the PCNT changes are known in a family, carrier testing can be offered to at-risk relatives.

Brain imaging and growth hormone decisions

Brain imaging of the blood vessels is recommended from diagnosis so that moyamoya or aneurysms can be found and treated early. Growth hormone should be avoided unless growth hormone deficiency is present.

References

  1. Duker A, Jackson A, Bober MB, 2021. Microcephalic Osteodysplastic Primordial Dwarfism Type II. GeneReviews
  2. PCNT gene. MedlinePlus Genetics
  3. Microcephalic osteodysplastic primordial dwarfism type II. MedlinePlus Genetics

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