What is Phelan-McDermid syndrome (PHMDS)?
Phelan-Mcdermid syndrome or 22q13 deletion syndrome as it is also known may trigger varying levels of symptoms. 75% of individuals diagnosed with the syndrome are also on the Autism spectrum.
This rare disease also presents with global developmental delay, intellectual disability, low muscle tone, and distinct facial features.
Syndrome Synonyms:
Chromosome 22q13.3 Deletion Syndrome; Telomeric 22q13 Monosomy Syndrome
What gene change causes Phelan-McDermid syndrome (PHMDS)?
The syndrome is caused by a continuous gene deletion in the distal long arm of chromosome 21. This usually affects the SHANK3 gene.
In the case of autosomal dominant inheritance just one parent is the carrier of the gene mutation, and they have a 50% chance of passing it onto each of their children. Syndromes inherited in an autosomal dominant inheritance are caused by just one copy of the gene mutation.
What are the main symptoms of Phelan-McDermid syndrome (PHMDS)?
Individuals with the syndrome experience varying symptoms and varying severity of symptoms. Individuals may have mild to severe intellectual disability, and most have delayed or absent speech. Motor delay is also common and issues with toilet training are also common. Individuals may also experience sleep disorders and feeding problems related to the syndrome.
Facial and physical characteristics include low muscle tone, large hands, misformed ears, dysplastic toenails, long eyelashes, a large head, flat midface, wide brow, wide nasal bridge, deep-set eyes, full cheeks and puffy eyelids.
Other health conditions include heart and kidney defects and epilepsy. Many individuals appear to experience a high pain tolerance and may sweat less leading to an increased risk of overheating.
Possible clinical traits/features:
Sporadic, Unsteady gait, Microcephaly, Short chin, Macrocephaly, Tongue thrusting, Toenail dysplasia, Ventricular septal defect, Umbilical hernia, Concave nasal ridge, Ptosis, Strabismus, Thick eyebrow, Large hands, Macrotia, Muscular hypotonia, Long philtrum, Long eyelashes, Lymphedema, Neonatal hypotonia, Neurological speech impairment, Tall stature, 2-3 toe syndactyly, Abnormal nasal morphology, Abnormality of immune system physiology, Intellectual disability, moderate, Cerebral cortical atrophy, Behavioral abnormality, Autism, Wide nasal bridge, Bulbous nose, Bruxism, Broad-based gait, Cellulitis, Abnormality of the periventricular white matter, Abnormality of the dentition, Abnormal eyelash morphology, Aggressive behavior, Accelerated skeletal maturation, Aplasia/Hypoplasia of the corpus callosum, Arachnoid cyst, Dolichocephaly, Ventriculomegaly, Cerebral visual impairment, Feeding difficulties in infancy, Motor delay, Malar flattening, Delayed CNS myelination, Impaired pain sensation, Dental malocclusion.
How is it diagnosed?
To find out if someone has a diagnosis of Phelan-McDermid syndrome (PHMDS), it is important to have a consultation and evaluation with a clinical genetic specialist. Specialists may also suggest specific genetic testing or other types of tests to help reach a diagnosis. FDNA’s AI technology can help speed up the diagnostic process by analyzing facial features and other health information.
