Young-Simpson Syndrome


Young-Simpson Syndrome

Description, Causes and Risk Factors:

Abbreviation: YSS.

Young-Simpson Syndrome is a rare genetic disorder, characterized by facial dysmorphisms including blepharophimosis and ptosis, congenital hypothyrodism, and mental retardation. It was first described by Young and Simpson in 1987. Only 13 patients have been reported in the literature to date. The majority of the reports have been published in the last few years because of the greater attention give to this disorder.

At present, the syndrome is poorly known to the endocrinologist and pediatricians, but it should be included in the diffrential diagnosis of congenital hypothyrodism. Theories varies regarding the Young Simpson Syndrome's mode of inheritance. One group suggests that is through an autosomal recessive inheritance while another group says its is not.

Young-Simpson Syndrome

This syndrome is characterised by the association of congenital hypothyroidism, facial dysmorphism (microcephaly, blepharophimosis, a bulbous nose, thin lip, low-set ears and micrognathia), postaxial polydactyly and severe intellectual deficit. Less than 20 cases have been reported so far. Cryptorchidism is present in affected males. Some patients also have cardiac anomalies (interventricular communication), hypotonia and growth delay. Autosomal recessive inheritance has been suggested. The evolution of cognitive, adaptive and behavioral characteristics is still unclear.

The mode of inheritance has had mixed findings based on studies undertaken. One study showed that the parents of an individual with Young-Simpson Syndrome are unrelated and phenotypically normal, indicating a sporadic mutation, thus making it difficult to base the cause of the condition on genetic make up alone. Another study however with an individual of Young-Simpson Syndrome had first cousins as parents, giving the possibility of autosomal recessive inheritance.

Research: Researchers studied a cohort of 19 individuals with a presumed diagnosis of YSS. Twelve individuals were considered to have typical features of the syndrome, 2 had suggestive but milder features, and 5 were classified as atypical. By whole-exome sequencing in 4 individuals with typical features, researchs identified heterozygous mutations in the KAT6B gene: a nonsense mutation (E1357X; 605880.0004) in individual 4 (E1357X), a 1-bp insertion (605880.0001) in individual 1, and a 2-bp deletion (605880.0002) in individual 2. Subsequently, all 19 individuals with an YSS or a YSS-like phenotype were sequenced for the entire KAT6B coding region by classic Sanger sequencing. Truncating mutations in exon 18 of the KAT6B gene were confirmed in 12 individuals, and individual 3 was found to have a heterozygous frameshift mutation in exon 15 (605880.0003), which had not been detected on whole-exome sequencing. When parental samples were available, the mutations were shown to have occurred de novo. Researchers suggested that mutations of protein-protein interaction domains in exon 18 result in a more complex phenotype than the phenotype due to simple haploinsufficiency of KAT6B and raised the possibility that exon 18 mutations are activating or have a dominant-negative effect.

Symptoms:

Manifestation of the syndrome includes:

    Hypothyroidism.

  • Heart defects.

  • Facial dysmorphism.

  • Cryptorchidism in males.

  • Mental retardation and torticollis.

Diagnosis:

The diagnosis of Young-Simpson syndrome remains a clinical one and is usually made by a clinical geneticist on the basis of the physical features, after exclusion of other causes. There are some other syndromes associated with blepharophimosis which have features that overlap with Young-Simpson Syndrome type and these include blepharophimosis-ptosis-epicanthus inversus syndrome (BPES). There is no specific test for Young-Simpson Syndrome as yet.

Treatment:

There is no specific cure or treatment for Young-Simpson Syndrome, but a number of therapies may help at different stages of life. These include physiotherapy, occupational therapy and a detailed assessment of special educational needs. There should be regular review by a pediatrician and thyroid function should be checked every one to two years, or if symptoms develop.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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