When I consider all of the different patients with a birth anomalies that I have the privilege to evaluate and treat, there is no question that symbrachydactyly is the diagnosis most often misnamed or unnamed. Amniotic constriction band is perhaps most commonly given as the incorrect diagnosis for the patients.
Symbrachydactyly literally means short, webbed fingers. And that certainly can be how patients with symbrachydactyly present as I have previously shared here- Previous Post. While there are 7 types (depending on your favorite classification), in my mind there are two types which are most common. All seven seem to be related to the same issue, and not a genetic one. We believe that a lack of blood supply to the developing limb is most likely the cause of symbrachydactyly and the timing determines the severity, the type.
The short finger type of symbrachydactyly is really the type that best fits with the name. The fingers are shortened due to a short or absent middle phalanx and the fingers are also commonly webbed. The other common type is the “cleft” type symbrachydactyly in which the thumb and little finger are normal or close to normal and the index, middle, and ring fingers are notably short and may be only a nubbin.
Here are two great examples of these two types of symbrachydactyly. First, the short finger type. This patient had surgery to separate the fingers at about 18 months of age and is functioning at a high level and is satisfied with appearance.
|Short finger symbrachydactyly. Note the middle phalanx is abnormal.|
|Short finger symbrachydactyly. Close examination shows the surgical scars from web deepening.|
|Short finger symbrachydactyly.|
The other common type of symbrachydactyly is the cleft type. The painted fingernails help visualization. And the nubbins are small bones (distal phalanx) with nails that develop from the ectoderm after the vascular insult affects the mesoderm in the developing arm.
|Cleft type symbrachydactyly. Note the three nubbins in the cleft.|
|Cleft type symbrachydactyly. Note the thumb is normal and the little finger is more, but not normally developed as the middle phalanx is absent.|
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What would you say is the reason this happens? Im a new mom to a baby with severe symbrachdactyl. You say “vascular” but what do you mean by that. Thanks so much
The theory is that the blood supply to the developing limb is decreased or completely stops. We don't know why that might happen but models for this theory make sense. We do not believe this is a genetic condition. The mesodermal tissue (called the progress zone) looses blood supply and development stops. So, if an early insult happens, the development of the arm stops earlier and, for example, there may be a below elbow level issue. A later insult could mean only the hand is affected. Early and late mean, approximately, 30 vs 40 days of gestation, so not so dramatically different from a time perspective. Finally, the ectodermal tissues (apical ectodermal ridge) are not affected- we believe that explains why most kids with symbrachydactyly have fingernails and/ or nubbins.
Do you have any preferred theories on what could cause the interruption in blood flow? I cant help but baae myself for this happening to our daughter. Thank you so much.
We really don't know what might cause a decreased blood supply. We have not identified any action by a mom that leads to this. It is natural to have that sense and want to blame yourself but science does not support that thought. Love your daughter and she will do great.
My great granddaughter was born in Dec with thumb hyplosia on both hands. Early in pregnancy her mother had a subchorionic hemmorrage <50% could this have caused a decrease in blood supply?
Symbrachydactyly is, we believe, related to decreased blood flow to the developing extremity. Hypoplastic thumb is a different condition and has a different etiology (and is often genetic). Having clarified this, there could be a relation between the conditions but I am not aware of it.
Is there research into the cause of symbrachdactyly that you are involved in or aware of?
Thank you for the question. Actually yes, we are embarking on a genetic study with a large number of kids. We are about to submit a grant for funding this effort. Of course, it will take a few years to share results but I am optimistic that we can take a few steps forward.