Wiedemann–Steiner syndrome (WSS)^[2] is a rare genetic disorder that causes developmental delay, unusual facial features, short stature, and reduction in muscle tone (hypotonia). The syndrome was originally described in 1989^[3] by Hans-Rudolf Wiedemann. The genetic basis for the syndrome was identified by Dr. Wendy D. Jones in 2012.^[4] The first case was reported in 1989 by Wiedemann and colleagues which reported a Caucasian boy with pre- and postnatal growth deficiency, psychomotor delay, and a round and flat face, short nose, widely spaced eyes, long philtrum, short palpebral fissures, low-set ears, and high-arched palate. Other findings included an alternating convergent squint, dilatation of the renal calyces, and short and thick limbs. Later decades brought about more finding and descriptions of this disorder.^[5]

Features described in Wiedemann–Steiner syndrome include:^[6]

• Short stature
• Developmental delay
• Low muscle tone (hypotonia) especially in infancy
• Characteristic facial features
• Hairy elbows (hypertrichosis cubiti)

Wiedemann–Steiner syndrome results from mutations in the MLL (also known as KMT2A) gene on the long arm of chromosome 11.^[4] The gene encodes a histone-modification enzyme — that is, it helps modify the expression of other genes.^[5] The condition is autosomal dominant, meaning that only one abnormal copy of the gene is needed for a person to have the syndrome.

The mechanism by which mutations in the MLL gene cause the phenotype of Wiedemann–Steiner syndrome is not yet known.^[5]

If Wiedemann–Steiner syndrome is suspected, analysis of the MLL gene can be carried out. Otherwise, it may be diagnosed by whole-exome sequencing or whole genome sequencing.

There have also been patients with Wiedemann–Steiner syndrome who were initially mis-diagnosed with Kabuki syndrome.^[7]

There is no specific cure or treatment for Wiedemann–Steiner syndrome. Children with this condition may benefit from a range of supportive treatments such as physiotherapy, speech therapy, supplementary nutrition for poor feeding, and special educational support.^[6]

A little over 1000 people have been documented with the condition worldwide. Once thought to have an incidence of 1 in 1,000,000, some research has suggested the incidence may be as high as 1 in 40,000 ^[5] The approximate number of WSS cases are seemingly low today but offspring of those with WSS have half the chance of having the disorder themselves.^[2] There’s no current evidence of life expectancy of individuals with WSS is shortened.^[7]